District of Sechelt Preliminary Report

District of Sechelt 

Preliminary Report 

This report is prepared for the sole use of the District of Sechelt. 

No representations of any kind are made by Urban Systems Ltd. 

or its employees to any party with whom Urban Systems Ltd. does 

not have a contract. 

#304 - 1353 Ellis Street 

Kelowna BC V1Y 1Z9 

Telephone: 250-762-2517 

Fax: 250-763-5266


Bio-Solids Processing Options Report 

TABLE OF CONTENTS 

EXECUTIVE SUMMARY ......................................................................................................... ES-1 

1.0 INTRODUCTION .................................................................................................................. 1 

1.1 SUBJECT AND PURPOSE ............................................................................................................. 1 

1.2 SCOPE .................................................................................................................................. 1 

1.3 METHODOLOGY ....................................................................................................................... 1 

2.0 PROJECT HISTORY ............................................................................................................. 2 

2.1 BACKGROUND ......................................................................................................................... 2 

2.2 PRE-DESIGN METHODOLOGY ...................................................................................................... 3 

3.0 BIOSOLIDS PRODUCTION .................................................................................................. 7 

3.1 WHAT ARE BIOSOLIDS .............................................................................................................. 7 

3.2 THE MECHANISM OF BIOSOLIDS PRODUCTION ................................................................................. 7 

3.3 BIOSOLIDS QUANTITY ESTIMATES ................................................................................................ 8 

4.0 RECYCLING BIOSOLIDS ...................................................................................................12 

4.1 BIOSOLIDS REGULATIONS ........................................................................................................ 12 

4.1.1 Class A and Class B Biosolids .................................................................................. 12 

4.1.2 Class A and Class B Compost .................................................................................. 13 

4.1.3 Biosolids Growing Medium ...................................................................................... 13 

4.2 OTHER QUALITY PARAMETERS .................................................................................................. 13 

4.3 SITE SELECTION .................................................................................................................... 14 

4.4 THE INITIAL SITES EXAMINED ................................................................................................... 14 

4.5 THE SITE COMPARISON CRITERIA .............................................................................................. 15 

4.6 SITE A ................................................................................................................................ 15 

4.7 SITE B ................................................................................................................................ 16 

4.8 SITE C ................................................................................................................................ 16 

4.9 FURTHER INVESTIGATION OF LOT L ............................................................................................ 17 

4.10 SITE ASSESSMENTS OF LOT L ................................................................................................... 17 

5.0 BIOSOLIDS TRANSFER .....................................................................................................20 

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5.1 OPTIONS EXAMINED ............................................................................................................... 20 

6.0 BIOSOLIDS STABILIZATION ............................................................................................21 

6.1 STABILIZATION REQUIREMENTS ................................................................................................. 21 

6.2 COMPARISON OF PROCESSES .................................................................................................... 22 

6.3 DISCUSSION OF APPLICABILITY ................................................................................................. 24 

6.3.1 Anaerobic Digestion ............................................................................................... 24 

6.3.2 Aerobic Digestion ................................................................................................... 24 

6.3.3 Autothermal Thermophilic Aerobic Digestion (ATAD) ................................................ 24 

6.3.4 Composting ........................................................................................................... 25 

6.3.5 Thermal Processing ................................................................................................ 25 

6.3.6 Alkaline Stabilization ............................................................................................... 27 

7.0 BIOSOLIDS THICKENING .................................................................................................28 

7.1 THICKENING PROCESSES.......................................................................................................... 28 

7.1.1 Gravity Thickening ................................................................................................. 28 

7.1.2 Dissolved Air Flotation (DAF) .................................................................................. 28 

8.0 BIOSOLIDS DEWATERING ................................................................................................29 

8.1 DEWATERING PROCESSES ........................................................................................................ 29 

8.1.1 Belt Filter Press ...................................................................................................... 29 

8.1.2 Centrifuges ............................................................................................................ 29 

8.1.3 Pressure Filter Press ............................................................................................... 30 

8.1.4 Screw Press ........................................................................................................... 30 

8.2 DEWATERING PROCESS COMPARISON .......................................................................................... 30 

9.0 BIOSOLIDS HEAT DRYING ...............................................................................................36 

9.1 DESCRIPTION ....................................................................................................................... 36 

9.2 APPLICABILITY ...................................................................................................................... 36 

9.3 ADVANTAGES AND DISADVANTAGES ............................................................................................ 36 

9.3.1 Advantages ........................................................................................................... 36 

9.3.2 Disadvantages ....................................................................................................... 37 

9.4 END-PRODUCT CHARACTERISTICS .............................................................................................. 38 

9.4.1 Odours .................................................................................................................. 38 

9.4.2 Nutrient Content .................................................................................................... 38 

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9.4.3 Mechanical Durability ............................................................................................. 38 

9.4.4 Particle Size Distribution ......................................................................................... 38 

9.4.5 Moisture Content ................................................................................................... 38 

9.4.6 Dust Content ......................................................................................................... 39 

9.5 TYPES OF DRYERS .................................................................................................................. 39 

9.5.1 Direct Dryers ......................................................................................................... 39 

9.5.2 Indirect Dryers ....................................................................................................... 39 

10.0 SHORT-LISTED TECHNOLOGIES .......................................................................................41 

10.1 STABILIZATION ..................................................................................................................... 41 

10.2 THICKENING ......................................................................................................................... 41 

10.3 DEWATERING ....................................................................................................................... 42 

10.4 THERMAL DRYING .................................................................................................................. 42 

11.0 THE SEWAGE FORCEMAIN ................................................................................................43 

12.0 EBB TIDE PLANT IMPROVEMENTS ...................................................................................44 

13.0 ODOURS & NOISE .............................................................................................................45 

13.1 CRITICAL CONTROL POINTS AND ODOUR SOURCES ......................................................................... 45 

13.2 WHAT IS ODOUR? ................................................................................................................. 45 

13.2.1 Primary Biosolids Odourants ................................................................................... 45 

13.3 FACTORS AFFECTING ULTIMATE ODOUR POTENTIAL AT CRITICAL CONTROL POINT 1: THE WWTP ............ 46 

13.4 FACTORS AFFECTING ULTIMATE ODOUR POTENTIAL AT CRITICAL CONTROL POINT 2: THE TRANSPORTATION 

PROCESS ................................................................................................................................ 48 

13.5 FACTORS AFFECTING ULTIMATE ODOUR POTENTIAL AT CRITICAL CONTROL POINT 3: THE FIELD STORAGE 

SITE 49 

14.0 APPLICABLE PROCESS TRAINS ........................................................................................50 

14.1 END PRODUCTS ..................................................................................................................... 50 

14.2 SOME FUNDAMENTAL CRITERIA ................................................................................................. 50 

14.3 CLASS B PROCESS TRAINS ....................................................................................................... 51 

14.4 CLASS A PROCESS TRAINS ....................................................................................................... 51 

14.5 PROCESS COST SUMMARY ........................................................................................................ 52 

14.6 DISCUSSION ......................................................................................................................... 53 

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FIGURES 

Figure 2.1 

Figure 2.2 

Figure 2.3 

Figure 3.1 

Figure 3.2 

Figure 4.1 

Figure 8.1 

Figure 8.2 

Sewage Treatment Plant sites 

Existing System Schematic 

Biosolids Transfer Schematic 

Historical flow Data 

Recent Flow Data 

Lot L Site 

Biosolids Processing Schematic 

Preliminary Site Layout 

APPENDICES 

Appendix A Environmental Screening, Archaeological Assessment & Geotechnical Assessment 

Appendix B Technical Memorandum #1 

Appendix C Cost Estimates 

Appendix D Photos 

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EXECUTIVE SUMMARY 

The report examines the options for diverting biosolids (sludge) from the two existing District of Sechelt 

sewage treatment plants to a site where it can be properly processed. The site (referred to as the Lot L 

site) is to ultimately become the site for a new single central sewage treatment facility. In the short term, 

however, it is to accommodate a biosolids treatment facility. 

The initial exercise deals with the methods of transferring biosolids to the new site. This is documented in 

Technical Memorandum #1 (included in Appendix A of this report). 

The report addresses the biosolids processing options to achieve a product that can safely be used as a 

soil amendment anywhere in the region. 

The processes examined include: 

 

 

 

Stabilization: by digestion (aerobic or anaerobic) or by lime addition. 

Dewatering: by a variety of technologies such as belt filter press or centrifuge. 

Drying: by composting or mechanical heat drying technologies. 

Stabilization is defined in the BC OMRR (Organic Matter Recycling Regulation) for Class A products and 

Class B products used for recycling. Class A products must meet strict pathogen kill parameters through 

either high temperature or high pH. Temperature requirements can be met by multi-stage anaerobic 

digestion; pH requirements can be met by lime addition. Class B parameters can be met by aerobic 

digestion. In either case, stabilization alone yields (on average) a 4% solids content product, which can 

be handled much like water. 

Dewatering processes are used to “squeeze” water from the product in order to produce a lower volume 

of material. Dewatering does not further stabilize the product. It achieves (on average) a 20% solids 

content product. This product is of a thick slurry consistency and results in lower hauling costs, being 5 

times less volume than the 4% product. 

Drying processes achieve 90% or greater solids content and result in a dry granular, easy to transport 

material. Drying can be achieved by composting or by mechanical heat drying. Both methods achieve the 

temperature required for significant pathogen kill and are classed as Class A products. Composting 

requires mixing dewatered biosolids with a drying and bulking agent such as wood chips. Heat drying 

applies heat to dewatered biosolids in a rotating kiln. Composting requires a much larger area and is a 

much slower process. 

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The analyses and comparisons undertaken in the study conclude the following: 

 

 

The most economical process for achieving Class A biosolids is thickening, dewatering and heat 

drying at a capital cost of $5,535,000. This process can be undertaken at the Lot L site within an 

enclosed building. The dried granular product can be hauled for mine reclamation, or disposed at 

the landfill, or sold directly to consumers. 

The most economical method of achieving Class B biosolids is aerobic digestion followed by 

dewatering at a capital cost of $4,227,000. This product is a thick viscous slurry that can be 

applied directly to the tree planting operation for mine reclamation, or mixed with wood chips 

and composted to produce a Class A compost. ( A readily available composting site has not 

been identified). 

The annual operation and maintenance costs of producing Class A biosolids by dewatering and heat 

drying is estimated at $120,000. per year. Hauling of this product to the mine reclamation site is 

estimated at $10,000. per year, yielding a total annual cost of $130,000. per year. The cost of application 

of the product is not included 

The annual operation and maintenance cost of producing Class B biosolids by aerobic digestion and 

dewatering is estimated at $95,000. per year. Hauling of the product to the mine reclamation site is 

estimated at $75,000. per year for a total annual cost of $170,000 per year. The cost of application of the 

product is not included. Composting at a more remote site is possible and would achieve a Class A 

compost. The cost of composting has not been estimated at this point site a site for such an activity has 

not been identified. 

Present worth comparisons are made on the basis of a a 20-year horizon using a compound interest rate 

of 5% per annum. A summary of the two options follows: 

Class A : Thickening, Dewatering and Heat Drying 

Capital cost: $5,535,000. 

Annual O&M: 

120,000. per year 

Annual Hauling: 

10,000. per year 

Present Worth: $7,155,000. 

Class B: Aerobic Digestion and Dewatering 

Capital cost: $4,227,000. 

Annual O&M: 


Annual Hauling: 


Present Worth: $6,341,000. 

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In both cases, the base assumption is that the products would be used for soild amendment in the tre 

planting operation of the mine reclamation project. In the case of the Class A dried granular material, 

other options are available. 

There is a greater capital investment required to produce a Class A biosolids product at the Lot L site of 

approximately $1.3 million. The annual processing cost is also higher. However, the hauling costs are 

reduced from $75,000 per year to $10,000 per year. Overall, it results in a Present Worth difference of 

approximately $520,000. 

The improvements at the Ebb Tide plant required for safety and greater efficiency ar estimated at 

$600,000. The combined cost of aerobic digestion and dewatering for a Class B product results in a total 

of $4,827,000.; very close to the current $4.8 million budget. 

The investment required to produce a dried Class A biosolids product is $6,006,000.; or roughly $1.2 

million over the current budget. This additional funding must come from the District of Sechelt, as the 

Federal/Provincial contribution $3.2 million is a fixed amount. 

Page ES-3 

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Bio-Solids Treatment Pre-Design Report 

1.0 INTRODUCTION 

1.1 Subject and Purpose 

This study presents an investigation and comparison of options for treating sewage treatment plant 

residuals from the existing District of Sechelt plants. Sewage treatment plant residuals are commonly 

referred to as sludge or biosolids. 

The purpose of the report is to enable selection of the best process for dealing with biosolids and 

producing a product which can be reclaimed in accordance with the B.C. Organic Matter Recycling 

Regulation (OMRR). 

1.2 Scope 

This report will deal with the biosolids products from the two existing sewage treatment plants and the 

trucked waste from the region, currently received at the Dusty Road treatment plant.. A previous report 

provides a comparison of a variety of sewage treatment technologies which could be used in the future 

construction of a single central sewage treatment plant. 

This report will deal with options for conveyance of biosolids to the new site and the options available for 

processing the biosolids. The end-use considerations are explored in a separate document entitled 

“Biosolids Management Plan”. The Biosolids Management Plan examines options for use of processed 

biosolids such as agricultural uses, tree planting and site reclamation, landfill cover material and soil 

amendment products. 

1.3 Methodology 

The study initially examines the routes and options for diverting biosolids from the two existing plants to 

the new site. This is documented in Technical Memorandum No.1 appended to this report. 

This report develops the quantities of biosolids generated, both currently and in the future. It compares 

applicable technologies available for stabilization, dewatering and drying. This is followed by a discussion 

of the potential destination of the variety of potential products derived from biosolids processing, 

including local opportunities such as tree planting for the gravel mining reclamation programs. 

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2.0 PROJECT HISTORY 

2.1 Background 

The District of Sechelt operates two sanitary sewage treatment plants, which treat sewage from the 

community collection system in the District. The plants are referred to as the Ebb Tide plant and the 

Dusty Road plant. 

Both plants produce treated effluent which is discharged through an ocean outfall into Trail Bay. The 

discharge is authorized by the Ministry of Environment Permit #PE-04088, last amended in November, 

2008. 

The two sewage treatment plants produce a residuals stream (biosolids) which must be dealt with. The 

Ebb Tide plant does not have any facilities for treating biosolids and biosolids are mixed into the sewage 

pump station which pumps to the Dusty Road plant. The Dusty Road plant also receives trucked waste 

from the region. 

The introduction of Ebb Tide plant biosolids to the Dusty Road plant significantly increases the organic 

loading at the Dusty Road plant and compromises its treatment capacity. 

Over the last several years the District has assessed options for providing continued service into the 

future. The goal has been to develop an appropriate strategy and business plan for the utility to keep 

pace with growth in the community. 

The Ebb Tide plant is located in a relatively small site. It is also in close proximity to a residential area, 

and odour and noise are a concern. The Dusty Road plant is located on leased land. The owner of the 

land has declared that the lease will not be renewed when it terminates in 2031. 

The District therefore decided to pursue the concept of a new centralized plant to replace both Ebb Tide 

plant and Dusty Road plant in the long term. 

A further consideration in the District’s wastewater strategy relates to the condition of the forcemain 

which transfers sewage from the Ebb Tide site to the Dusty Road site. This forcemain developed leaks in 

1998 and in several subsequent years. The investigation of these leaks in the year 2001 resulted in 

several modifications to reduce the risk and severity of leakage. The report on the forcemain 

investigation is available for supplementary readings. While these modifications have mitigated the 

leakage, the high pressure in the pipe continues to be a concern. 

One of the criteria for the site selection included an elevation which would result in reduced pressure in 

the forcemain, and consequently reduce the risk of leakage. 

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After several years of searching, the District purchased a site at the foot of Dusty Road (Lot L, Plan 

LWMP49852, DL 1438), 3.5 Hectare size. This site is at elevation 40 – 30 m above mean sea level, or 

almost 70 m below the Dusty Road site and 35 m above the Ebb Tide site. This lower elevation 

represents a reduction of roughly 100 psi in the forcemain static pressure. The site is referred to as the 

“Lot L” site. 

Figure 2.1 shows the location of the three sites. Appendix A provides the initial Environmental 

Screening, Archaeological Assessment and Geotechnical Assessment for the site. 

2.2 Pre-Design Methodology 

A search for suitable sites was conducted, and the Lot L site was selected for a future single centralized 

sewage treatment plant. In the short term, the capacity of the Ebb Tide plant and the Dusty Road plant 

could be improved by dealing with the residual biosolids issue. A schematic depiction of the existing 

treatment facilities is provided in Figure 2.2. 

The concept of an initial biosolids facility was assessed further, cost estimates developed, and an 

application submitted for senior government funding assistance under the “Building Canada” program. 

The approximate cost estimate for the project was $4.8 Million, including a provision for upgrades to the 

Ebb Tide treatment plant. The biosolids processing concept was based on utilizing the Lot L site for 

several reasons: 

 

 

 

The Ebb Tide site does not have sufficient space for additional facilities. 

The Dusty Road site is to be decommissioned when the lease expires. 

The Lot L site will be utilized for a future centralized sewage treatment plant. 

The application for funding was approved and the District commissioned the pre-design phase of the 

project. One of the critical aspects of the project is the ability to transfer biosolids from the Ebb Tide 

plant and the Dusty Road plant to the Lot L. The options for this transfer were examined in Technical 

Memorandum No.1, which is included here as Appendix B. 

Technical Memorandum No. 1 was discussed at a meeting of the Sechelt Sewage Facilities Commission 

(SSFC), and later with the Sechelt Indian Band, LeHigh Aggregates Ltd. and the Sunshine Coast Regional 

District. The preferred option for the transfer of biosolids to the Lot L site is as follows: 

a. Construct a biosolids transfer pipe from Dusty Road plant to the Lot L site. This would be a 

gravity pipe constructed on Dusty Road. 

b. Convert a currently unused tank at the Ebb Tide plant to a biosolids storage tank, and pump this 

volume through the existing forcemain to the new site, alternatively cycling with the existing raw 

sewage pumps. 

A schematic depiction of the preferred biosolids transfer option is provided on Figure 2.3. 

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Bio-Solids Facilities Pre-Design Report 

Lot L 

DUSTY ROAD 

TREATMENT 

PLANT 

EBB TIDE 

TREATMENT 

PLANT 

° 

0 400 

Meters 

SUITE 304 - 1353 ELLIS STREET 

KELOWNA, BC, CANADA V1Y 1Z9 

Tel. 250.762.2517 

Fax. 250.762.5266 

www.urban-systems.com 


Bio-Solids Facilities Pre-Design Report 

USL File 

1592.0026.01 

XXXX.YYYY.ZZ 

Date 

September, 2010 

Client/Project 

Figure 

2.1 

Title 

Sewage Treatment Plant Sites



3.0 BIOSOLIDS PRODUCTION 

3.1 What are Biosolids 

Biosolids are the organic solids product of municipal wastewater treatment that can be beneficially 

utilized. Raw biosolids emanate from any wastewater treatment process and are typically 98% to 99% 

liquid before processing. This liquid is not suitable for direct use and must be processed to stabilize 

volatile compounds, and reduce pathogens. Pathogens are defined as disease-causing micro-organisms 

including certain bacteria, viruses, fungi and protozoa. 

3.2 The Mechanism of Biosolids Production 

Sewage treatment plants utilize the natural biological processes of microbiological consumption to reduce 

the amount of organics in wastewater. A colony of benign micro-organisms is maintained in a reactor by 

the provision of oxygen and food. The “food” consists of the incoming organics in the sewage and 

biosolids returned from the clarifier. When this balance of food to micro-organism ratio is maintained, the 

plant functions efficiently. 

The quantity of biosolids returned from the clarifier to the bioreactor is periodically adjusted by the 

operator to maintain the required balance. The biosolids not required for the balance are referred to as 

“waste biosolids” and must be removed from the process. 

The “waste” biosolids are typically further processed in a sidestream to achieve stabilization (converting 

volatile biosolids into gas) and thickening. In order to reduce handling costs, the thickened biosolids 

slurry is also “dewatered”, either mechanically or with sand drying beds. Dewatering transforms the slurry 

into a moist “cake”. 

The relative concentrations of dry solids in each of the above products is: 

 

 

 

Clarifier biosolids: 1 - 2% (10,000 – 20,000 mg/L) 

Digested or thickened biosolids: 3 – 4% (30,000 – 40,000 mg/L) 

Dewatered biosolids: 20 – 22% (200,000 – 220,000 mg/L) 

Dewatered biosolids can be further dried by thermal drying to achieve up to 95% solids concentration. 

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3.3 Biosolids Quantity Estimates 

The District of Sechelt sewage treatment plants utilize bioreactors and clarifiers. The clarifier biosolids are 

partly returned to the bioreactor and partly removed from the process. 

There is no further processing of excess biosolids at the Ebb Tide plant. Excess biosolids are disposed of 

to the sewage pump station, blended with raw sewage and pumped to the Dusty Road plant. 

Excess biosolids at the Dusty Road plant are diverted to an open pond equipped with subsurface 

aerators. Trucked waste (septage) is also deposited in this pond. Photo 1 in Appendix D shows the 

surface of the aerated pond. 

The aerated pond overflows to an adjacent non-aerated pond for settling. Photo 2 in Appendix D shows 

the surface of the non-aerated pond. A surface skimmer in the non-aerated pond directs the surface 

liquid back to the bioreactor. 

The solids mixture in the non-aerated pond is pumped out by a pumper truck and hauled to the poplar 

plantation where it is applied as fertilizer for the trees. 

The estimates for production of biosolids involve multiplying the daily flow by the concentration of 

suspended solids. The following is an estimate of average daily production: 

Influent 2,500 m³/d x 0.25 kg/m³ = 625.0 kg/d (dry solids) 

Effluent 2,500 m³/d x 0.045 kg/m³ = 112.5 kg/d (dry solids) 

Removed 

512.5 kg/d (dry solids 

This correlates with the recorded quantity of biosolids currently disposed of. The quantity provided in the 

Sylvis annual reports is 500 loads per season, each at 8.2 m³, for a total of 4,100 m³/year. The solids 

concentration is reported as 5% (50 kg/m³) so the total dry solids removed is 4,100 x 50 = 205,000 

kg/year. On a daily basis, this equates to 205,000/365 = 561.6 kg/day, representing a close correlation 

to the calculated quantity of 513 kg/day. 

The difference between 513 and 562 kg/d accounts for the “trucked” waste. Trucked waste includes 

septic tank pump-outs and waste sludge pump-outs from approximately 20 neighbourhood package 

plants in the region. 50 kg of dry solids per day is the equivalent of 5 m³/day at 1% concentration. 

Figure 3.1 provides a historical summary of recorded treatment plant flows. Figure 3.2 provides the 

last two years of flow recordings. The average daily flow is approximately 2300 m³/d. The projection for 

the 20-year term is 4000 m³/d, as average daily flow. 

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The quantities of biosolids to be currently dealt with (from both plants) are: 

Clarifier waste biosolids (1%): 

Trucked waste biosolids (1%): 

Thickened or digested biosolids (3%): 

Dewatered biosolids (20%): 

51 m³/d 

5 m³/d 

18.7 m³/d 

2.8 m³/d 

The projected quantities when the total sewage flow reaches 4,000 m³/d are: 

Clarifier waste biosolids (1%): 

Trucked waste biosolids (1%): 

Thickened or digested biosolids (3%): 

Dewatered biosolids (20%): 

82 m³/d 

8 m³/d 

30 m³/d 

4.5 m³/d 

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4.0 RECYCLING BIOSOLIDS 

4.1 Biosolids Regulations 

The regulations in BC which govern the recycling of biosolids are contained in the BC OMRR (Organic 

Matter Recycling Regulation) deposited in 2002 and updated on June 30, 2007 (BC Reg 198/2007) 

The OMRR contains definitions of organic matter under five classes. The definitions describe the products 

defined by processing criteria as well as quality criteria. 

The products are classified under the headings of Compost products (Class A and Class B), Biosolids 

products (Class A and Class B), and Biosolids Growing Medium. The Compost products (Class A and Class 

B) and the Biosolids Growing Medium are relatively dry and can be handled easily. These composted soil 

amendment products are a mixture of biosolids (Nitrogen source) and wood products (Carbon source) 

with Carbon:Nitrogen ratios ranging from 15:1 to 35:1. 

Biosolids products (Class A & Class B) can be in slurry form (2 to 5% solids), or in a thicker dewatered 

consistency (18 to 22% solids “cake”), or as a dried granular or pellet form (85 to 95% solids). 

4.1.1 Class A and Class B Biosolids 

Class B biosolids are achieved by processes which reduce volatiles and pathogens by aerobic or anaerobic 

digestion or by alkaline treatment. 

Class A biosolids are achieved using processes to “further reduce pathogens”. These include 

pasteurization, drying or heat treatment and advanced alkaline treatment. The Class A product can be 

used in most areas with minor restrictions. 

The pathogen indicator is Coliform bacteria. The OMRR requires maximum counts of (expressed as 

mpn/g = most probable number per gram): 

 

 

Less than 1,000 mpn/g for Class A 

Less than 2,000,000 mpn/g for Class B 

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4.1.2 Class A and Class B Compost 

Composting involves the mixing of a Carbon containing product such as wood with biosolids (Nitrogen). 

The Carbon and Nitrogen combination creates reactions that produce heat, drying and conversion of 

volatiles to gas. The length of composting, temperatures achieved and time of maturation result in either 

a Class A or a Class B compost. The probable pathogen kill is determined by the Coliform test. The 

measurement used as an indicator of pathogens is Coliform bacteria. The OMRR requires Coliform 

bacteria counts of: 

 

 

Less than 1,000 mpn/g for Class A compost 

Less than 2,000 mpn/g for Class B compost 

4.1.3 Biosolids Growing Medium 

This product is typically produced by mixing Class B biosolids with granular material such as sand and 

wood waste or yard waste products (typically clipped) to form a material that is relatively dry, easily 

spread and used as a matrix for growing grass, shrubs or trees. The coliform count must be under 1,000 

mpn/g. 

4.2 Other Quality Parameters 

The OMRR also provides other quality parameters for recycled products. These include the metals 

concentrations shown in Table 4.1 below. 

Table 4:1 OMRR Metal Concentrations 

Maximum Element Concentration (mpn/g dry wt) 

Class A 

Compost 

Class B 

Compost 

Class A 

Biosolids 

Class B 

Biosolids 

Biosolids 

Growing 

Medium 

District of 

Sechelt 

Biosolids 

Arsenic 13 75 75 75 13 4.3 

Cadmium 3 20 20 20 1.5 2.8 

Chromium 210 1,060 1,060 1,060 100 21.2 

Cobalt 34 150 150 150 34 2.5 

Copper 400 2,200 757 1,200 150 686 

Lead 150 500 500 500 150 41.7 

Mercury 2 15 5 15 .8 2.48 

Molybdenum 5 20 20 20 5 6.4 

Nickel 62 180 180 180 62 15.4 

Selenium 2 14 14 14 62 8.1 

Zinc 500 1,850 1,850 1,850 150 1,000 

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As indicated above, under the OMRR there is the need to comply with both quality and process 

requirements. The process requirements relate to pathogen reduction and vector attraction reduction. 

The requirements for pathogen reduction are outlines in Schedule 1 of the OMRR. There are more 

stringent treatment requirements for a Class A biosolids/Class A compost which relate to a period of time 

when elevated temperature of the material (i.e. ≥ 50 o C) is required. If these elevated temperatures are 

not met, then the Class A designation cannot apply, resulting in a Class B product instead. 

The last column in Table 4.1 provides the recorded data from the regular sampling of the District of 

Sechelt biosolids over the last 2 years. It’s evident that in terms of metals concentrations, the biosolids 

meet the Class A parameters. The photo’s in Appendix D show the tree plantation and the growing 

medium stock pile operated by Sylvis Environmental Inc. 

This indicates that the key concern with respect to recycling biosolids relates to pathogens and the 

processes applied to achieve sufficient pathogen kill for either a Class A or a Class B product. 

4.3 Site Selection 

The initial site selection was targeted at a site which could be used for biosolids processing and also have 

sufficient area for a future centralized sewage treatment plant. 

Composting operations, if applicable, would be undertaken at a larger more remote site. 

4.4 The Initial Sites Examined 

The District’s initial efforts focussed on areas which could make full use of the existing forcemains and 

effluent outfall pipes as well as resolve the problem of high pressure in the forcemain. This areas was in 

the vicinity of the Dusty road/East Porpoise Bay Road intersection. Three potential sites presented 

themselves: 

Site A: owned by CAL (Construction Aggregates Ltd.) east of the campground on East Porpoise Bay 

Road. 

Site B: owned by CAL, east of Lot L on Dusty Road. 

Site C: Lot L, the Lot L property on Dusty Road. 

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4.5 The Site Comparison Criteria 

The sites were compared using some basic parameters: 

 

 

 

 

 

 

 

 

 

 

 

 

Elevation (above sea level) 

Available construction area 

Tree cover 

Soils and groundwater conditions 

Current zoning 

Adjacent land uses 

Proximity to 3-phase power 

Noise and odour factors 

Access 

Archaeological concerns 

Pumping and energy requirements 

Environmental concerns 

4.6 Site A 

Site A was offered by CAL with the condition that they be allowed to mine the existing gravel prior to 

treatment plant construction. The mining would create a “pit” roughly 7 metres below existing ground. 

The resulting drop in ground elevation would make access difficult and would result in cutting the berm 

on Dusty Road. 

An alternate access is possible by utilizing the BC Hydro Right-of Way with connection to the existing 

road network at the CAL site. Although this creates some geometry and earthworks issues, they do not 

appear insurmountable. The top of tank elevation would be approximately 35m above sea level and the 

pumping requirement from the Ebb Tide site would result in much lower pressures in the forcemain. 

Power to the site is easily available, but the land is dedicated for gravel extraction. In this case the gravel 

would be extracted prior to treatment plant construction. Tree cover would not be available for screening 

and would need to be planted. The impacted land is the campground immediately adjacent to the west. 

The site is large enough to accommodate the treatment plant and sludge processing facilities. The gravel 

mining operation will have already addressed any archaeological concerns. The initial overview did not 

identify any environmental concerns. 

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Notwithstanding the access and earthwork difficulties, the District pursued this negotiation and acquired 

this site through expropriation. Later difficulties with the mining plan resulted in a substitute offer by CAL 

of an alternate site higher up on Dusty Road (Site B). 

4.7 Site B 

Site B was offered by CAL for consideration as an alternate to Site A. Here again, the condition was that 

the site be mined and the gravel extracted prior to construction of the sewage treatment plant. While the 

overall area is slightly over 7 Hectares, the net usable area is much smaller when taking into account 

these additional factors: 

 

 

 

The 30m setback required from the existing creek 

Mining of gravels down to elevation 50m ASL 

2:1 cut slopes 

The remaining site for construction of a sewage treatment facility is approximately 1.6 Hectare. This site 

could possibly accommodate a plant of 6000 m 3 /day capacity but would not allow for any future 

expansion. 

The average finished grade elevation of 50m ASL would result in a pressure in the forcemain of 85 to 90 

psi. This pressure is roughly half of what is currently required to pump the full design flow to the Dusty 

Road site (170 psi) at elevation 110m ASL. 

The site is heavily treed, but it’s expected that all the trees would be removed by the gravel mining 

operation. Re-planting would be necessary for screening. Access from Dusty Road is reasonable at the 

low end after the mining is completed. 

Given the limitations of small net area, this site was not pursued further. 

4.8 Site C 

Site C (Lot L) lies immediately west of Site B. It has a gross area of 3.5 Hectares and a net area of 2.9 

Hectares, excluding the BC Hydro Right-of Way and an easement of the NE corner. The site elevation 

ranges from 25m ASL at the low end (west) to 40m ASL at the high end (east). The north-south gradient 

is relatively flat. 

The site has been partially logged, but the eastern half remains treed. The land is zoned light industrial 

and is currently used for nursery operations. The site is large enough to accommodate the facility and 

future growth as well as a planted buffer zone. Three phase power runs through the western edge in a 

BC Hydro RoW. Access off Dusty Road is good. 

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There are residential areas to the north, and west of East Porpoise Bay Road. However, visual screening 

on all sides is achievable. The facility would require noise and odour control features. 

The site appeared to meet most of the selection criteria and some initial screening activities were 

commissioned. These included a geotechnical/hydrogeological overview, a habitat and environmental 

overview and an archaeological screening. All initial investigations did not reveal any issues with these 

factors and the District proceeded to purchase the site. 

4.9 Further Investigation of Lot L 

Lot L lies at the west end of Dusty Road near the intersection of East Porpoise Bay Road. It is bounded 

on the north side by Allen Road. The property is Lot L, DL 1438, Plan LMP49852. It is currently being 

used as a tree and shrub nursery and for storage of landscaping products. 

The elevation of the site ranges from 40 m. above sea level on the east side to 28 m above sea level on 

the west side. A driveway through the site, starting at on Allen Road at the NE corner and connecting to 

Dusty Road, requires further investigation. 

An air photo of the site is provided on Figure 4.1 Photos 3 and 4 in Appendix D present ground level 

views of the existing site. 

4.10 Site Assessments of Lot L 

Preliminary site assessments were undertaken by: 

a. IRC (Integrated Resource Consultants Inc.) 

A stage 1 preliminary environmental assessment 

b. Peter Merchant 

Archaeological Assessment Report (Shishalh Nation Rights and Title Department) 

c. Geotactic Media Engineering (2007) Ltd. 

Geotechnical appraisal with 5 test pits 

These reports are included in Appendix A. 

The environmental assessment provides the minimum required setback from Irgens Creek high water 

mark (10 m). It also recommends that the gate at Allen Road be closed to reduce the risk of HADD 

(Harmful Alteration Disruption or Destruction) of fish habitat. 

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The archaeological overview indicates that there are no recorded archaeological sites located within the 

subject area. 

The geotechnical investigation indicates the presence of silty sands and gravels with no identifiable 

hazards for construction of structures. Structures would have to be designed for post-seismic code for the 

region. Accordingly, deeper boreholes should be undertaken prior to final design. 

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5.0 BIOSOLIDS TRANSFER 

5.1 Options Examined 

Technical Memorandum No. 1 (included as Appendix B) explored several methods to transfer biosolids 

from the Ebb Tide site and the Dusty Road site to the Lot L site. 

The options were discussed with the District of Sechelt, the SSFC and LeHigh Aggregates. The preferred 

option was to construct a new transfer pipe on Dusty Road from the plant to the Lot L site 

(approximately 600 m length). The transfer of Ebb Tide biosolids would be achieved with the existing 

forcemain by cycling between the raw sewage pump and the biosolids pump. 

The cycling procedure would require that the forcemain be purged each time sludge is to be pumped. 

The volume of the forcemain (from Ebb Tide to Lot L site) is approximately 216 m³. The existing pump is 

sized for a rate of 4.7 m³/min. It would purge the pipe in 46 minutes. An automatic valve at the 

discharge end would divert to the biosolids chamber after the appropriate delay time. 

There is storage already available at the Ebb Tide site of approximately 150 m³. If 120 m³ is utilized to 

store 3 days of biosolids production, the pump cycling would be approximately as follows: 

1. Regular raw sewage pumping to raw sewage chamber 

2. When biosolids chamber is close to full, continue pumping to raw sewage chamber for 

approximately 35 minutes 

3. Activate diversion valve to biosolids chamber after 35 minutes 

4. Pump to biosolids chamber for 25 minutes (120 m³ @ 4.7 m³/min) 

5. Activate diversion valve back to raw sewage chamber, begin pumping raw sewage 

The procedure may flow through a small amount of biosolids with raw sewage at the beginning and end 

of each cycle, but the ratio will be very small and will not impact the treatment plant operation. Biosolids 

storage at the site will require odour control. 

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6.0 BIOSOLIDS STABILIZATION 

6.1 Stabilization Requirements 

“Stabilization” of biosolids refers to processes that convert the volatile fraction of biosolids to gas and 

water. Stabilization processes also reduce pathogens and provide a less odorous product for use or 

disposal. There are five proven stabilization processes: 

1. Anaerobic digestion 

2. Aerobic digestion 

3. Autothermal thermophilic aerobic digestion 

4. Composting 

5. Alkaline stabilization 

The digestion processes achieve natural decomposition of micro-organisms. Aerobic digestion achieves it 

with the use of oxygen. Anaerobic digestion achieves a similar result but with the use of methane forming 

micro-organisms. Thermophilic digestion combines aeration and heat to speed up the process. 

Composting is also a natural decomposition process. It requires a carbon source to combine with the 

nitrogen in the biosolids. The carbon source is typically a wood product such as wood ships or hog fuel. 

Alkaline stabilization is typically achieved by lime addition (Calcium Hydroxide). The chemical reaction 

raises the pH as well as the temperature and results in rapid die-off of pathogens. 

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6.2 Comparison of Processes 

Table 6.1 provides some of the advantages and disadvantages of each process. 

Table 6.1: Comparison of Stabilization Processes 

Process Advantages Disadvantages 

Anaerobic Digestion Good volatile suspended solids 

destruction (40 to 60%) 

Net operational costs ban be low 

if gas (methane) is used 

Broad applicability 

Biosolids suitable for agricultural 

use 

Good pathogen inactivation 

Reduces total sludge mass 

Low net energy requirements 

Aerobic Digestion Low initial cost, particularly for 

small plants 

Supernatant less objectionable 

than anaerobic 

Simple operational control 

Broad applicability 

Odours are “earthy” and low 

concentrations that can be 

controlled 

Reduces total sludge mass 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Requires skilled operators 

May experience foaming 

Methane formers are slow 

growing; hence, “acid digester” 

sometime occurs 

Recovers slowly from upset 

Supernatant strong in 

carbonaceous oxygen demand, 

biochemical oxygen demand, 

suspended soils, and ammonia 

Cleaning is difficult (scum and 

grit) 

Can generate nuisance odours 

resulting from anaerobic nature of 

process 

High initial cost 

Potential for struvite (mineral 

deposit) 

Safety issues concerned with 

flammable gas 

High energy costs 

Generally lower volatile 

suspended solids destruction than 

anaerobic 

Reduced pH and alkalinity 

Potential for pathogen spread 

through aerosol drift 

Biosolids typically are difficult to 

dewater by mechanical means 

Cold temperatures adversely 

affect performance 

May experience foaming 

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Process Advantages Disadvantages 

Autothermal 

Thermophilic Aerobic 

Digestion 

 

 

 

 

Reduced hydraulic retention 

compared with conventional 

aerobic digestion 

Volume reduction 

Excess heat can be used for 

building heat 

Pasteurization of the sludge, 

pathogen reduction 

 

 

 

 

High energy costs 

Potential of foaming 

Requires skilled operators 

Potential for odours 

Composting High-quality, potentially saleable 

product suitable for agricultural 

use 

Can be combined with other 

processes 

Low initial cost (static pile and 

window) 

Lime Stabilization Low capital cost 

Easy operation 

Good as interim or emergency 

stabilization method 

Advanced Alkaline 

Stabilization 

 

 

 

Produces a high-quality Class A 

product 

Can be started quickly 

Excellent pathogen reduction 

Sludge Dryers Substantially reduces volume 

Can be combined with other 

processes 

Produce a Class A product 

Not a biological process so it can 

be started quickly 

Retains nutrients 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Requires 18 to 30% dewatered 

solids 

Requires bulking agent 

Requires either forced air (power) 

or turning (labour) 

Potential for pathogen spread 

through dust 

High operation cost: can be 

power, labour, or chemical 

intensive, or all three 

May require significant land area 

Requires carbon source 


Biosolids not always appropriate 

for land application 

Chemical intensive 

Overall cost very site specific 

Volume of biosolids to be 

disposed of is increased 

pH drop after treatment can lead 

to odours and biological growth 

Operator intensive 

Chemical intensive 


Volume of biosolids to be 

disposed of is increased 

May require significant land area 

Some dryers could be labour 

intensive 

Produces an off gas that must be 

treated 

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6.3 Discussion of Applicability 

6.3.1 Anaerobic Digestion 

Anaerobic digestion is widely used in larger plants, typically greater than 20,000 m³/d. The Sechelt plants 

currently process an average of 2,500 m³/d. The advantages of methane production is diminished when 

quantities are small. The presence of anaerobic bacteria increases the risk of offensive odours with 

process upsets. 

The anaerobic digestion process is the result of a complicated set of chemical and biochemical reactions, 

in the context of an ecosystem involving many types of micro-organism. 

The first stage consists of hydrolysis, which converts complex organics to soluble organics. Soluble 

organics are, in turn, converted to organics which form methanogens, methane and carbon dioxide. 

The methane requires “scrubbing” to be used for energy production. In small plants, the quantity of 

methane produced makes it uneconomical to provide a gas scrubbing and energy recovery system. 

6.3.2 Aerobic Digestion 

Aerobic digestion is a suspended growth biological process based on the activated sludge theories. It is a 

process more commonly used in smaller plants (less than 20,000 m³/d) results in an inoffensive 

biologically stable product. It is relatively simple to operate and odours can be controlled. There is no 

production of methane. 

Aerobic digestion is based on the principle of endogenous respiration. This occurs when the supply of 

available substrate (food) is depleted and micro-organisms begin to consume their own protoplasm to 

obtain energy for cell maintenance. The cell tissue is oxidized aerobically to carbon dioxide, water and 

ammonia or nitrates. Typically 75 – 80% of cell tissue is oxidized. The remaining 20 – 25% is composed 

of inert components and organic compounds that are not biodegradable. Consequently, it is stable and 

suitable for a variety of disposal or reuse options. 

6.3.3 Autothermal Thermophilic Aerobic Digestion (ATAD) 

The ATAD process is a variation of aerobic digestion that achieves operating temperatures of 40 – 80ºC 

without supplemental heat beyond that supplied by mixing. The process can achieve in excess of 35% 

volatile solids destruction and sufficient pathogen reduction to meet Class A designation, under the 

OMRR. 

This process is applicable to smaller plants, but requires significantly more process control than an 

aerobic digester. The consistency of the inflow biosolids is critical, and a thickener is recommended prior 

to ATAD feed. The risk of odours is relatively high. 

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The variable characteristics of incoming biosolids in this base (both primary and secondary biosolids) 

adds a measure of complexity and additional operational control to the ATAD process. The requirement 

for pre-thickening to 3 -5% solids content increases the capital cost. 

6.3.4 Composting 

Composting is a self-heating process that destroys pathogens and produces a material similar to soil 

humus. Well-stabilized compost can be stored indefinitely and has minimal odour, even if re-wetted. It is 

suitable for a variety of end uses. 

A medium is required for composting that is dry enough to act as a bulking agent (35 – 50% solids) but 

wet enough to sustain biological activity. Wood products such as chips or hog fuel are an ideal source of 

Carbon to combine with the Nitrogen in the biosolids. The ideal Carbon to Nitrogen ratio is 30:1. 

The commonly used methods of composting are: 

a. Aerated static pile 

b. Windrow process 

In-vessel composting, using a silo or tunnel, is also practiced, but it is significantly more costly and not 

widely used. 

6.3.5 Thermal Processing 

Thermal processes include: 

 

 

 

Thermal conditioning 

Thermal drying 

Thermal destruction 

Thermal conditioning refers to the simultaneous application of heat and pressure to enhance the 

dewaterability of the biosolids without the use of chemicals. However, biosolids must be thickened to at 

least 6% solids concentration before thermal conditioning can be applied. Thermal conditioning is useful 

because it can improve mechanical dewatering if a 30 – 40% cake is required. It is, however, energy 

intensive. 

Thermal drying involves the application of sufficient heat to evaporate water. The drying process is 

usually undertaken in three stages: warm-up stage, constant-rate stage, and falling-rate stage. The heat 

transfer methods include convection, conduction, and radiation or combinations of these. Direct dryers 

include flash dryers and rotary dryers (kilns). The drying process is highly energy consumptive and costly. 

It is appropriate if the goal is to achieve a 60-90% solids content product. 

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Thermal destruction refers to incineration and involves extremely high temperatures. Incineration is often 

considered in a regional context if biosolids can be combined with other waste products from other 

sources and provisions are made for control of air emissions. 

Thermal processes were not considered further due to their high cost and the relatively small quantities 

of biosolids to be dealt with. 

Table 6.2 provides a brief comparison of composting processes. 

Table 6.2: Key Advantages and Disadvantage of Composting Systems 

Composting 

Technology 

Advantages 

Disadvantages 

Aerated Static Pile Adaptability to various bulking 

agents 

Flexibility to handle changing feed 

conditions and peak loads 

(volume not fixed) 

Relatively simple mechanical 

equipment 

Windrow Adaptability to various bulking 

agents 

Flexibility to handle changing feed 

conditions and peak loads 

(volume not fixed) 

Relatively simple mechanical 

equipment 

Requires no fixed mechanical 

equipment 

Vertical Plug Flow Completely enclosed reactors in 

some systems improve ability to 

control odours 

 

 

Relatively smaller area required 

Operators not exposed to 

composting material 

 

 

 

 

 

 

 

 

 

 

 

 

 

Relatively labour intensive 

Relatively large area required 

Operators exposed to 

composting piles 

Potentially dusty working 

environment 

Very large area required 

Relatively labour intensive 



Dusty working conditions 

Single outfeed device per reactor 

(large reactors), potentially 

bottleneck 

Potentially inability to maintain 

uniform aerobic conditions 

throughout reactor 

Relatively maintenance intensive 

Limited flexibility to handle 

changing conditions 

Materials-handling system may 

limit choice of bulking agents 

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Composting 

Technology 

Advantages 

Disadvantages 

Horizontal Plug Flow 

(tunnel) 

 

 

 

Completely enclosed reactors 

improve ability to control odours 

Relatively smaller area required 

(compost mix compacted) 

Operators not exposed to 

composting material 

 

 

 

 

Fixed-volume reactors (no 

flexibility) 

Limited ability to handle 

changing conditions 


Materials-handling system may 

limit choice of bulking agents 

Agitated Bin Mixing enhances aeration and 

uniformity of compost mixtures 

Ability to mix compost (advantage 

in handling some bulking agents) 

Adaptability to various bulking 

agents 

 

 

 

 

 

Fixed-volume reactors (no 

flexibility) 

Relatively large area required 

Potentially dusty working 

environment 




6.3.6 Alkaline Stabilization 

The addition of alkaline chemicals is a reliable method of stabilization. Quicklime and hydrated lime are 

the most common alkaline additives. Lime stabilization is a common practice at small treatment plants. 

Liquid lime is commonly used on liquid biosolids. The process requires a storage silo, volumetric feeders 

and mixing tanks. Dry lime stabilization is used on dewatered biosolids cake. 

The primary disadvantage of lime stabilization, when compared to digestion, is that there is no reduction 

in solids mass. In fact, mass is increased because of the added lime and chemical formations. With 

proper mixing, alkaline stabilization can reduce odour risks. 

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7.0 BIOSOLIDS THICKENING 

7.1 Thickening Processes 

Thickening is used as an intermediate step prior to some stabilization processes such as ATAD or prior to 

dewatering. It provides some beneficial results such as homogenizing primary and secondary biosolids 

and reducing the hydraulic loading to subsequent processes. Thickening is not required prior to aerobic 

and anaerobic digestion since these processes inherently thicken biosolids. 

The most common methods for thickening are: 

a. Gravity thickening 

b. Dissolved Air Flotation 

Other mechanical methods include centrifugation, belt thickening and rotary drums. These methods 

require more operator time and are not as widely used as gravity thickening and dissolved air flotation. 

7.1.1 Gravity Thickening 

A gravity thickener is, in essence, a settling tank, with a bottom collector mechanism. The most common 

configuration is a circular tank with a side-water depth of 3 to 4 m. The size should be large enough to 

allow a quiescent settling time, but not so large as to result in anaerobic conditions due to long detention 

time. 

Gravity thickening can achieve 2 – 3% solids concentration of secondary biosolids and 4 – 6% solids on 

combined primary and secondary biosolids. The process is energy efficient. 

7.1.2 Dissolved Air Flotation (DAF) 

Dissolved air flotation (DAF) has become more widely used because of its relatively small footprint. It 

consists of introducing a stream of fine air bubbles to the liquid; the resultant buoyancy of the particles 

causes the matrix to rise to the surface where it is collected by a skimming mechanism. 

DAF is widely used for secondary biosolids (activated sludge), but not generally used on primary 

biosolids. Where space is critical, DAF has advantages over gravity thickening. However, DAF incurs 

greater power costs due to the horsepower required for the air saturation pumps. Float solids 

concentration can be up to 3 to 4%. 

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8.0 BIOSOLIDS DEWATERING 

8.1 Dewatering Processes 

Historical dewatering of biosolids was typically achieved with the use of sand beds and under drains. 

These drying beds required a long detention time and a labour-intensive scraping procedure for removal 

of the dewatered product. Wet weather significantly hindered the dewatering process. 

More modern methods utilize mechanical liquid/solid separation techniques. The most common include: 

a. Belt Filter Press 

b. Centrifuge 

c. Pressure Filter 

d. Screw Press 

8.1.1 Belt Filter Press 

This is a sequential process that includes chemical conditioning, gravity drainage to a non-fluid 

consistency and compaction in a pressure and shear zone 

A continuous porous belt provides a large surface area through which drainage occurs. The compression 

stage squeezes the product between two belts and results in further dewatering. 

Belt filter presses are more effective with primary and anaerobic digested sludge. The flocs in secondary 

biosolids are more difficult to dewater and belt filter presses have difficulty achieving a cake of more than 

15% solids concentration. Anaerobically digested biosolids can be dewatered with a belt filter press up to 

20% solids. 

8.1.2 Centrifuges 

A centrifuge achieves liquid/solid separation by spinning at high speed much like the spin cycle on a 

washing machine. Solid bowl centrifuges use centrifuged force of 500 to 3,000 times the force of gravity. 

Centrifuges are applicable to many different types of biosolids, but pre-conditioning with a polymer or 

metal salt is required. Organic polymers are usually the most cost effective and have better performance 

characteristics. 

Centrifuges are totally enclosed and the risk of odours is less than open belt filter presses. Some odour 

may be present on the cake discharge end. The cake is typically discharged with a screw conveyor to a 

truck or bin. Centrifuges have an excellent safety record. 

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8.1.3 Pressure Filter Press 

A pressure filter press system can produce a cake with greater than 30% solids concentration. Pressure 

filtration separates solids from a liquid slurry using positive pressure differential as the driving force. 

The pumping forces the liquid through a filter medium, leaving a concentrated solids cake trapped 

between the filter cloths that cover the recessed plates. When the plates are separated, the cake drops 

downward to a conveyor. Pre-conditioning with polymer is essential for the process. 

Pressure filter presses are generally higher capital cost than other processes, and require more labour to 

operate, washing of the filter media is required after each batch. 

8.1.4 Screw Press 

The screw press concept was typically used for thickening, but the technology has evolved to the point 

where a cake of up to 20% solids concentration is achievable. 

The screw press utilizes a low speed auger with a conical screw shaft and cylindrical sleeves consisting of 

three zones: inlet/drive zone, thickening/dewatering zone, and press zone. The advantage of the screw 

press is reduced wear due to low speed operation. The cake solids concentration can vary, and piloting is 

recommended. 

8.2 Dewatering Process Comparison 

Table 8.1 presents a comparison of various parameters for the four dewatering technologies described 

above. Figure 8.1 presents s schematic depiction of the processes discussed, and Figure 8.2 presents 

a preliminary site layout for the process components. 

Page 30 

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Table 8.1: Comparison of Centrifuges and Belt Filter Presses 

Centrifuge Belt Filter Press Pressure Filter Press Screw Press 

a. Cost 

Centrifuges may offer lower 

Typically viewed as a lower cost 

Highest capital costs and 

Low capital cost – 

Effectiveness 

overall operation and 

option compared to the 

highest O&M costs – 

solids content not 

maintenance costs and can 

outperform conventional belt 

centrifuge, but cannot achieve 

the same solids content as a 

achieves high solids 

content. 

guaranteed. 

filter presses in terms of dry 

centrifuge. 

solids produced. 

b. Floor Space Centrifuges require a small 

amount of floor space relative 

Belt presses require more space 

than a centrifuge for the same 

Largest floor space 

requirement. 

Low floor-space 

requirement. 

to their capacity. Less than half 

capacity. 

the space required for belt filter 

presses. 

c. Operator 

Attention 

Centrifuges require minimal 

operator attention when 

Needs frequent staff attention. 

Staffing requirements can be 

Significant set up, take 

down and cleaning time. 

Operator requirement is 

relatively low, cleaning 

operations are stable. Modern 

minimized, if the equipment is 

is simple. 

control elements take care of 

operation fluctuations 

large enough to process the 

solids in one shift. 

automatically. 

Belt presses require more 

operator attention if the feed 

solids vary in their solids 

concentration or organic matter. 

Page 31 

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d. Odours Operators have low exposure to 

pathogens, aerosols, hydrogen 

Odours may be a problem, but 

can be controlled with good 

Odours may be a 

problem. 

Odour formation is 

minimal – unit is fully 

sulphide or other odours. 

ventilation systems and 

enclosed. 

chemicals, such as potassium 

Some exposure to 

permanganate, to neutralize 

odour-causing compounds. There 

aerosols in the wash 

cycle. 

is still a concern of exposure to 

pathogens. 

e. Cleaning Centrifuges are easy to clean 

Belt washing at the end of each 

Washing is a lengthy 

Minimal hose down 

and use less water for cleaning. 

shift, or more frequently, can be 

process. 

requirements. 

time consuming and require large 

amounts of water during the 

cleaning operation, which ends up 

at head of plant. 

f. Resiliency Centrifuges can handle higher 

than design loadings and the 

Wastewater solids with higher 

concentrations of oil and grease 

Batch process can deal 

with a fixed volume for 

Fully automatic 

continuous operation. 

percent solids recovery can 

can result in blinding of the belt 

each batch. Higher 

Wear is minimized due 

usually be maintained with the 

addition of a higher polymer 

filter and lower solids content 

cake. Belt presses are solids 

volumes mean more 

frequent pressing. 

to low speed. 

dosage. 

limited. 

Page 32 

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g. Wear Factors The centrifuge has fast moving 

components which can be 

The belt press is vulnerable to 

tearing of the fabric filter. 

Filter medium can be 

damaged by rocks or 

Few wear parts, low 

speed and wide 

damaged or cause serious 

sharp objects. 

tolerance results in 

damage if rocks enter the 

minimal wear. 

equipment. 

Page 33 

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10m Bu er (Typ.) 

Creek 

Setback Area 

Irgens Creek 

Future Sewage 

Treatment Plant Area 

Trucked Waste 

Delivery 

Trucked Waste Drop-o and 

Dewatered Biosolids Bin 

10m Bu er (Typ.) 

Dewatering Building 

& Pump Station


Bio-Solids Processing Options Comparison Pre-Design Report 

9.0 BIOSOLIDS HEAT DRYING 

9.1 Description 

Heat drying, in which heat from direct or indirect dryers is used to evaporate water from wastewater 

solids., is one of several methods that can be used to reduce the volume and improve the quality of 

wastewater biosolids. A major advantage of heat drying versus other biosolids improvement methods, 

however, is that heat drying is ideal for producing Class A biosolids. Heat drying may become a 

requirement in the future. 

9.2 Applicability 

Heat drying is applicable in both urban and suburban settings because it requires a relatively small 

amount of land and facility design allows process air to be captured for treatment. Markets for dried 

products are generally more prevalent in suburban and rural areas than in urban settings. However, 

because heat drying reduces the volume of the solids to such a great extent, transport of the endproduct 

from urban areas to rural markets is usually economical. Heat drying is also becoming more costeffective 

even for small systems (



 

 

 

 

Can be designed to accept a variety of feed material characteristics. 

Greatly reduces the volume of material that needs to be transported. The typical heat-dried 

product is at least 90% solids commonly produced by mechanical dewatering operations. This 

feature is particularly important for major urban areas, where the end-product might need to be 

transported for considerable distances for use in marketing. 

Reduces traffic into and out of facility. The number of trucks required to remove material is 

reduced because of the smaller volume of the final biosolids product. In addition, no additives or 

amendments need to be transported into the facility. 

Generates a readily marketable product. 

9.3.2 Disadvantages 

Requires a substantial capital investment. Capital costs often are weighed against the long-term 

financial return that can be realized by the sale of the heat-dried pellets. 

 

 

 

 

 

Requires a large amount of energy. Heat-drying systems can require 1,400-1,700 British thermal 

units per pound of water evaporated. This makes heat drying less energy-efficient per pound of 

final material than other beneficial reuse methods, such as composting and land application. 

(Sapienza and Bauer 2005). In some cases, this can be at least partially offset through the use of 

on-site energy sources. For example, some facilities use gas from their anaerobic digesters to 

fuel the heat-drying units. Wood chips have also been used as a fuel source to produce the hot 

gases used in direct dryers. Recycling of these gases also reduces fuel costs. 

Generates dust that can affect plant workers and neighbours in the local community and must be 

controlled to avoid problems during storage and transport of the product. The health effects of 

the dust are similar to those caused by exposure to other sources of dust and primarily affect 

lung function. Controls are available to address dust concerns. Dust control is further discussed in 

the “System Design Considerations” section below. 

Creates an explosive hazard from dust generated in the drying process. (Sieger and Burrowes 

(2006)) Dryer installations have experienced fires, deflagrations, and explosions. Much of the 

recent work in thermal drying systems has been focused on enhancing their safety. (See 

discussions of thermal drying safety in the “Design Criteria” and “Performance” sections below.) 

Requires systems that are relatively complex in comparison with other solids-processing systems 

and need skilled labour for operation and maintenance. 

Can produce nuisance odours that could negatively affect community acceptance of the process. 

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9.4 End-Product Characteristics 

Heat-drying systems are typically designed to produce Class A biosolids. Although Class B biosolids can 

be produced using a heat-drying system, the lower market value of a Class B product typically does not 

justify the energy and cost required to run the system. 

9.4.1 Odours 

It is preferable that the pellets be free of offensive odours. Undigested solids tend to create more 

odorous pellets than those made from digested or waste-activated solids. Odours can increase if the 

pellets become wet, which can happen from condensation during cooling or through other mechanisms. 

The best way to reduce odours in the finished product is to continue to digest prior to dewatering and 

drying. In addition, the end-product must be properly stored to ensure that it is not exposed to moisture 

before use. Exposure to significant moisture presents a potential for anaerobic decomposition (leading to 

odours). 

9.4.2 Nutrient Content 

One of the main reasons that heat-dried biosolids can be sold and used as fertilizer is their nutrient 

content. Heat-dried biosolids pellets contain up to 6% nitrogen, up to 5% phosphorus, and a trace of 

potassium. Sufficient nutrients must be present in the biosolids to warrant the costs associated with 

transporting and applying them as fertilizer. A reliable sampling program must be established to 

determine the nutrient content, and this information should be provided to potential users (NBP 2005). 

9.4.3 Mechanical Durability 

It is important to ensure that the product will maintain its form through bagging, conveyance, handling, 

and storage. Pellets that are not within the standard range for mechanical durability may crumble during 

handling; therefore, they may not be acceptable even if they have sufficient nutrient content. 

9.4.4 Particle Size Distribution 

Pellets produced by heat-drying wastewaters and are angular in shape. Screening and sizing abrade the 

pellets into a more spherical shape. Irregular particle sizes can result in larger particles settling faster 

than smaller ones. Some users (such as fertilizer blenders) must ensure that products remain well mixed 

throughout shipment to their customers. End users may associate irregular pellet sizes with an inferior 

product. 

9.4.5 Moisture Content 

Too much moisture in the pellets can cause odour problems and might also cause the pellets to 

smoulder. Adequate cooling before the pellets are stored or transported will reduce the potential for 

odour and smouldering, and therefore this step should be included as part of the facility’s biosolids 

process. 

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9.4.6 Dust Content 

Dust from pellets can be problematic for several reasons. First, dust can be an explosion hazard. Second, 

dust might cause human health problems. And third, some potential end-users may not accept dusty 

pellets; since many potential users of biosolids pellets find excessive dust unacceptable or at least 

characteristic of an inferior product. Dust can be generated because the pellets were not sufficiently dried 

and hardened during heat-drying or because the pellets were not otherwise processed to minimize their 

potential to cause dust. 

9.5 Types of Dryers 

The most important feature of a heat-drying system is the dryer. Typically, the rest of the facility is 

designed around this integral piece of equipment. Dryer can be classified as direct or indirect. 

9.5.1 Direct Dryers 

In direct dryers, the wastewater solids come into contact with hot gases, which cause evaporation of 

moisture. 

Direct dryers, which include rotary dryers (the most common dryers in use today) flash dryers, spray 

dryers, the SWISS COMBI ecoDry process, and toroidal dryers, are most often the technology of choice 

when the product is intended to be marketed as an agricultural product. 

Pellets from direct dryers are usually uniform in texture, size, and durability, and therefore they rarely 

require additional processing to make them marketable. Generally, the plant must mix processed solids 

(usually undersized fine particles) into the feed solids to raise the solids content of the feed mixture and 

avoid a condition referred to as the “sticky” or “plastic” phase. This phase occurs in mixtures with 

between 40 and 60% solids, and it renders the material difficult to mix and move inside the dryer. 

9.5.2 Indirect Dryers 

In indirect dryers, the solids remain separated from the heating medium (usually thermal oil or steam) by 

metal walls, and the solids never some into direct contact with the heating medium. Moisture evaporates 

when the wastewater solids contact the metal surface heated by the hot medium. The heat transfer 

surface is composed of a series of hollow metal discs or paddles mounted on a rotating shaft, through 

which the heating medium flows. The rotating action of the shaft agitates the solids, improving heat 

transfer and facilitating the solids’ movement through the dryer. Mixing of previously dried material with 

feed solids is required in some indirect drying systems. 

Indirect dryers, which include steam dryers, hollow-flight dryers, and tray dryers, produce smaller 

quantities of noncondensable gas than direct dryers, which means that the process produces less odour 

and requires less odour control equipment. Indirect dryers usually have a higher thermal efficiency and 

are more suitable when pellets are to be used in energy production or combusted. Indirect dyers also 

produce less dust during the drying process and have a lower risk of explosion than direct dryers. 

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However, the end-product of indirect dryers (the pelletized material) tends to be dustier than a dried 

product from a direct dryer, and therefore it is not as marketable to some users. 

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10.0 SHORT-LISTED TECHNOLOGIES 

10.1 Stabilization 

The comparison of stabilization processes indicates that aerobic digestion and lime stabilization are 

appropriate for this application. 

Aerobic digestion has the advantage of volatile solids reduction, simplicity of operation, and inherent 

thickening. However, the product can be difficult to dewater mechanically as flocs do not easily release 

water. Pre-conditioning will be required before dewatering. 

Lime stabilization has the advantages of relatively simple operation, low capital costs and has the 

potential to produce a Class A product (pH of 12 or higher and temperature greater than 70˚C for 30 

minutes). The lime reaction is exothermic and will raise the temperature of the mixture. This method also 

results in better dewatering characteristics; however, the total solids mass is increased because of the 

lime addition. The process has a relatively high annual cost because of chemical consumption. 

Nevertheless it merits more detailed investigation and, at minimum, bench scale testing for effectiveness 

and development of design parameters. 

Anaerobic digestion is typically more costly for smaller plants and single stage reactors are usually 

insufficient for pathogen kill. Multi-stage anaerobic digesters are recommended if a Class A product is 

desired. 

Liquid lime stabilization is more commonly used over dry lime addition. Dry lime is more difficult to 

handle, requires dry chemical feeders and a pug mill to mix the dewatered biosolids cake. 

Calcium Hydroxide and Calcium Oxide (Quicklime) can both be used for stabilization. Calcium Hydroxide 

has a higher delivered cost, but since it has already been hydrated, a slaker is not required. A slaker is 

required for Quicklime. 

The selection of stabilizing chemical and the appropriate dosages for Sechelt biosolids should be 

undertaken with bench scale testing and pilot testing. Dosages of Calcium Hydroxide can range from 

0.1kg / kg dry solids to 0.3kg / kg dry solids. 

10.2 Thickening 

The most economical thickening process is gravity thickening. Thickening is not required if aerobic 

digestion is employed. Gravity thickening is useful prior to lime stabilization to enable concentration of 

solids and reduce the dosage of Calcium Hydroxide. Gravity thickening is also useful if the biosolids are to 

proceed directly to the dewatering process. 

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10.3 Dewatering 

The comparison shows that centrifuge dewatering is the most practical and least offensive process in 

terms of odour control. The screw press process may also be considered, but pilot testing should be 

undertaken to confirm its effectiveness. 

The supply only costs of a centrifuge system complete with a polymer pre-conditioning skid range from 

$250,000 to $350,000. The supply cost of a screw press complete with polymer injection system is 

approximately $250,000. Both have approximately the same floor space requirement. Both options can 

be considered in further detail before a final selection is made. 

10.4 Thermal Drying 

The most commonly used thermal drying process are rotary drum mechanisms with either direct heat 

(utilizing hot gases to cause evaporation), or indirect heat (thermal oil or steam jackets). Indirect dryers 

are more commonly used in smaller plants as they are easier to operate and require less energy. 

If an anaerobic digestion is used in conjunction with a dryer, the methane produced in the digester can 

be used as fuel to produce the heat required for the dryer. 

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11.0 THE SEWAGE FORCEMAIN 

The sewage forcemain (from Ebb Tide plant to the Dusty Road plant) was put into service in 1994. 

Breaks and leaks were noted in 1998. An investigation was undertaken in 2000, with a report on the 

investigation produced in November, 2001. 

Pursuant to the report, several modifications were made to reduce the risk of waterhammer in the pipe. 

These included an in-line check valve at the foot of Dusty Road as well as a pressure relief valve at that 

location. The examination of the pipe by Levelton Engineering Ltd. revealed: 

 

 

 

Inconsistent offset to the effluent pipe in the same trench. A too small offset results in 

inadequate sidewall support. 

Backfill compaction was less than specified. 

Joint deflections were greater than the supplier’s recommendations. 

The pipe was put back into service after installation of the check valve and pump control valves. It was 

pressure tested and operated on a limited basis at flow rates lower than design rates. 

The provisions of intermediate pumping at the Lot L site will have the effect of reducing the operating 

pressures in the pipe, as follows: 

 

 

Portion along East Porpoise Bay Road: from 160 psi to 50 psi. 

Portion along Dusty Road: from 130 psi to 100 psi. This reduction in operating pressure will 

mitigate the risk of leakage at the joint deflections. Splitting the forcemain into two sections will 

also reduce the risk of waterhammer. 

The pipe is PVC material, so corrosion is not an issue. Joint failure can still occur, but reduction of 

operating pressure from 160 to 50 psi will significantly reduce the risk of joint failure. The upgraded 

alarm and telemetry system will provide early warning of leakage and a response plan should be 

developed. The portion along Dusty Road will ultimately be eliminated as the Dusty Road plant is 

decommissioned prior to the lease termination. 

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12.0 EBB TIDE PLANT IMPROVEMENTS 

A site visit was conducted on July 8 and July 9 , 2010. The operation and condition of a variety of plant 

components were inspected and discussed with the operators. The following is a list of items to be 

repaired or replaced at the Ebb Tide plant. 

Description 

Capital Cost 

Estimate 

Water distribution lines (galvanized steel) of 25 and 50 mm 

diameter – badly rusted. $18,000 

Air lines (galvanizes steel) 50 mm diameter – badly rusted $15,000 

Explore feasibility of using effluent to supply the chlorinator 

(instead of municipal water) $4,000 

Replace the 100 mm diameter sludge air lift pipes $20,000 

Purchase and install a composite sampler (only grab samples are 

currently taken) $9,000 

Purchase and install an ultrasonic level monitor to re-activate the 

inlet Parshall flume flow recording $3,000 

New bar screen and screenings compactor. (The existing bar 

screen has a limited remaining life, and purchase of a new screen 

will depend on the time allotted for decommissioning of the plant.) $150,000 

Replace the clarifier gear drive $40,000 

Replace rusty handrails $30,000 

Install kick plates on all catwalks ( A WCB requirement) $8,000 

Replace the roof shingles on the plant superstructure. $24,000 

Install a floor drain and sump pump in the basement of the control 

building (emergency shower was installed recently to comply with 

WCB requirements, but there is no drain in the area). $8,000 

Chlorine automatic shut-off valves (WCB requirement) are being 

installed. $50,000 

Odour Control Improvements $70,000 

Sub-total $449,000 

Contingency and Engineering (35%) $157,000 

Total $606,000 

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13.0 ODOURS AND NOISE 

13.1 Critical Control Points and Odour Sources 

The wastewater treatment and biosolids processes have three “Critical Control Points”. 

These are: 

Point 1: 

Point 2: 

Point 3: 

the wastewater treatment facility 

the transportation process 

the field storage site 

Malodours are the single most important cause of public dissatisfaction with biosolids or other organics 

recycling and utilization project. Thus, odour control is a high priority. Experience and practice have 

demonstrated that biosolids and other organic by-products, such as animal manure, landscape trimmings, 

and food processing residuals, can be handled and processed without release of excessive malodourous 

compounds. However, if any of these materials, including biosolids, are poorly managed, then 

objectionable odours may develop during storage, and public acceptance of such a project will erode. 

13.2 What is Odour? 

The malodorous compounds (odorants) associated with biosolids, manures, and other organic materials 

are the volatile emissions generated from the chemical and microbial decomposition of organic nutrients. 

When inhaled, these odorants interact with the odour sensing apparatus (olfactory system) and the 

person perceives odour. 

Individual sensitivity to the quality and intensity of an odour compound can vary significantly and this 

variability accounts for the difference in sensory and physical responses experienced by individuals who 

inhale the same amounts and types of compounds. This distinction between “odour”, which is a sensation 

and “odourant”, which is a volatile chemical compound, is important for everyone who deals with the 

odour issue to recognize. When odour compounds are emitted into the air, individuals may or may not 

perceive an odour. 

13.2.1 Primary Biosolids Odourants 

The odour compounds generated, and most often detectable, at significant levels during biosolids 

treatment, storage, and use are ammonia, amines and reduced sulphur-containing compounds. Amines 

can be produced in easily detectable quantities during high temperature processes. Amines include: 

methylamine, ethylamine, trimethylamine, and diethylamine. Amines often accompany ammonia 

emissions, and if chlorine is used chloramines may be released. The sulphur compounds include 

compounds such as hydrogen sulphide, dimethyl sulphide, dimethyl disulfide, and methyl mercaptan. The 

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potential for these compounds to be annoying is based on part on their individual and combined quantity, 

intensity, pervasiveness, and character. 

13.3 Factors Affecting Ultimate Odour Potential at Critical Control Point 1: The WWTP 

The following section addresses Critical Control Point 1 issues. Specific situations and conditions 

associated with biosolids preparation at the WWTP are described along with their relation to storage and 

especially odours. When an odour situation cannot be averted, management of the emissions and quick 

response through mitigation practices are required to void creating nuisance odour situations. At the 

WWTP, which is Critical Control Point 1, this coordination includes: 

 

 

 

Assessing the stability of the biosolids before they leave the WWTP 

Having contingency plans to provide remedial treatment, or diversion of unacceptably odourous 

material to suitable land application or disposal sites. 

Notifying the storer and land applier of any changes in mixing (primary or secondary solids), 

polymer or other additives, pH, moisture content, or stability. 

Decisions relative to odour control are a series of trade-offs involving higher degrees of treatment at the 

WWTP versus the intensity of management at the off-site storage locations. Ensuring that the odour of 

biosolids leaving the WWTP is minimized is a key consideration, since it is more difficult to treat an odour 

problem that originated at the WWTP once the biosolids are placed at the storage site. In all cases, the 

temporary measures invoked to deal with unexpected and unanticipated events that lead to odours must 

be considered only as such. Persistent problems will require an examination of the treatment and 

handling processes to develop a better management approach. 

The potential for odourous emissions depends partly on the extent to which organic matter and nutrients 

are present in forms that microbes readily use. Stabilization processes may either: 1) decrease the level 

of volatile organic compounds and the availability of nutrients to reduce the potential for microbial 

generation of odours; or 2) change the physical or chemical characteristics of the biosolids in a way that 

inhibits microbial growth. Table 13.1 lists seven commonly used stabilization and/or processing 

methods. Odour issues associated with each method and/or process are shown along with appropriate 

corresponding prevention or remediation approaches. 

Odorous compounds within an enclosed area can be treated through the ventilation system with the use 

of Activated Carbon filters, Ozonation, Ultra-Violet light, or bio-filters. 

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Table 13.1 Prevention and management of odourous emissions associated with 

biosolids stabilization or processing methods 

Stabilization and 

Processing Methods 

Potential Causes of 

Odour Emissions 

Long Term 

Potential Solutions 

Short Term 

Temporary 

Solutions 

Anaerobic Digestion 

“Sour”, overloaded or 

thermophilic digester; 

volatilization of fatty 

acids and sulphur 

compounds 

Optimize digester; 

don’t overload 

Apply topical lime to 

stored biosolids 

Aerobic Digestion 

Low solids retention 

time: High organic 

loading, Poor aeration 

Increase retention 

time and aeration; 

Lower organic load 

Drying Beds 

Incomplete digestion 

of biosolids being 

dried 

Optimize digestion 

Compost 

Poor mixing of bulking 

agent; poor aeration; 

Improperly operating 

biofilters. 

Mix better; adjust 

mix ratio and aeration 

rate; improve biofilter 

function 

Aerate more 

effectively; remix; recompost. 

Alkaline 

Stabilization 

Addition of insufficient 

alkaline material so pH 

drops below 9, 

microbial 

decomposition may 

occur with generation 

of odorous 

compounds. Check 

compatibility of 

polymer with high pH 

and other additives, 

e.g. FeC1 3 . 

Increase pH 

Provide finer mesh 

grade of alkaline 

material and mix 

better to avoid 

inadequate contact 

with biosolids 

Check pH; apply 

topical lime 

Thermal 

Conditioning & 

Drying 

High temperature 

volatilization of fatty 

acids and sulphurcompounds 

Apply topical lime if 

biosolids are still liquid 

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Digested and Composted Biosolids 

Properly digested and/or composted biosolids meet stabilization and vector attraction reduction 

requirements because these extended treatments reduce pathogens and decompose volatile solids (i.e., 

the organic matter which serves as food for microbes). When such materials are placed in proper 

storage, they typically do not contain enough readily available nutrients to support a large, rapid growth 

of microbes that might generate odorous volatiles. 

Alkaline and Chlorine Treated Biosolids 

Chemical stabilization processes act to inhibit the growth of microorganisms, rather than to decompose 

the organic matter in the biosolids. Addition of alkaline materials, such as lime, elevates the pH to levels 

that suppress microbial activity and kill pathogens. As long as the pH remains high in stored materials, no 

new potential odorants will be produced. Small residual levels of reduced sulfur or amine compounds, 

which were generated prior to and not released during stabilization, may be present. One of the sulfur 

products of concern, hydrogen sulfide, is converted into a non-soluble (non-volatile) form at high pH. 

Raising the pH will liberate ammonia and amines, especially at the time of treatment. For the ammonia, 

this is unlikely to result in objectionable off-site impacts because ammonia is not a persistent odorant. 

However, amines can be persistent and are more likely detected off-site once ammonia has dissipated 

and thus stopped masking the amines. In addition, when stored, alkaline stabilized biosolids quickly 

develop a dry crust, which seals the pile and prevents significant volatilization. Disturbing piles during 

load-out operations exposes fresh surfaces to the atmosphere and increases the potential for 

volatilization of trapped residual odorous compounds. Hence, avoid load-out during air temperature 

inversions and periods of low turbulence, since pervasive odorants will more likely be detected under 

such conditions. 

Drying Beds and Thermal Drying etc. 

Heat and/or desiccation are the primary means of pathogen reduction in thermal treatment or drying; 

these methods also halt microbial decomposition of organic materials. They do not appreciably reduce 

organic matter during the relatively short time periods in which drying is conducted, and thus require 

appropriate management during storage to prevent significant resumption of microbial decomposition 

and release of odorants. 

13.4 Factors Affecting Ultimate Odor Potential at Critical Control Point 2: The 

Transportation Process 

The process of transporting biosolids from the generating facility to the field storage site may impede 

traffic, be unsightly and can potentially emit nuisance odors into the community. The transportation 

process (referred to as Critical Control Point 2 in this document) must be properly managed as to 

minimize these problems, including the public’s exposure to biosolids odors. One way to reduce public 

exposure to odors is to choose a hauling route that avoids densely populated residential areas. The fewer 

residences located along a hauling route, the less likely the general public will be annoyed by the traffic 

and biosolids odors. Making sure that the trucks used to haul biosolids are clean and well maintained is 

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another effective way to keep road surfaces clean and control odors during biosolids transport. Trucks 

should be cleaned before leaving the generating facility and after the biosolids have been deposited on 

the field storage site. These steps are important because odor concerns are exacerbated by increased 

road congestion, and by biosolids adhering to trucks and roadways. Hauling routes that avoid residential 

areas are also effective. 

13.5 Factors Affecting Ultimate Odor Potential at Critical Control Point 3: The Field Storage 

Site 

In most cases, biosolids produced at WWTPs with well-operated stabilization processes can be stored offsite 

without creating odor nuisances. However, if certain conditions occur while material is in storage, the 

potential for odorous emissions (sulfur- or amine-containing compounds or ammonia) will increase. 

13.6 Noise Management 

Noise at wastewater and biosolids treatment facilities typically arise from blowers or air compressors. 

When located within a building, the noise can be confined to the inside of the building through the use of 

appropriate building materials. Noise in the room can also be controlled with the use of noise dampening 

panels on walls and ceilings. 

Exterior noise at wastewater and biosolids facilities arises from trucks and equipment. Diesel engine 

noises and safety back-up beeper noise can carry over large distances. Control strategies including 

allowing truck and hauling operations to occur only during day time hours, restricting the size of 

equipment, and provision of sound absorptive barriers and trees at the site perimeter. 

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14.0 APPLICABLE PROCESS TRAINS 

14.1 End Products 

There are 5 potential end products from biosolids processing. The composting required for Class A or 

Class B compost must be performed at a more remote location. Even “in-vessel” composting incurs odour 

risks and it is not recommended that composting be undertaken at the Lot L site. 

Production of Class B biosolids is viable under the current agreements with Sylvis and LeHigh for mine 

reclamation. Class B biosolids can be achieved through aerobic or anaerobic digestion. Dewatering is also 

desirable to reduce hauling costs. 

Production of Class A biosolids can be achieved by multi-stage anaerobic digestion, advanced alkaline 

stabilization or by heat drying. 

Compost material can be achieved by any of the composting methods outlined. The classification of the 

compost as Class A or Class B will depend on the temperatures achieved during composting (greater than 

55 o C for atleast 3 days with the aerated static pile method). It is recommended that composting be 

undertaken at a separate site. 

Production of a Biosolids Growing Medium must also be undertaken at a separate site. A Biosolids 

growing medium can be derived from either Class A biosolids or Class B biosolids that meet the pathogen 

and vector attraction requirements and the metal concentration limits. 

14.2 Some Fundamental Criteria 

The Lot L site is close to some residential areas so the following assumptions have been adopted: 

 

 

 

Composting (if desired) will not be undertaken on Lot L, but at a more remote site. 

Since the existing ponds at the Dusty Road plant are to be decommissioned, storage of biosolids 

will be required. Storage can be provided at the Sylvis reclamation site, but only for dewatered 

biosolids. 

Processes at the Lot L site must have odour reduction and odour management techniques 

applied. 

A public meeting was held on October 25, 2010 and the following concerns were expressed: 

1. Odour and noise are the prime concerns of the neighbourhood residents and these two factors 

must be addressed in the facility. 

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2. The general public expressed a desire to produce a Class A product at the end of the process. 

3. The general public expressed a desire to produce a dried biosolids product for wider re-use 

opportunities. 

14.3 Class A Process Trains 

Sechelt’s biosolids currently meet OMRR Class A requirements for metals concentrations. However, a 

pathogen reduction process must be applied in order to meet the OMRR parameters. Aerobic digestion 

does not achieve the required temperatures. Single stage anaerobic digestion can achieve the required 

temperatures but not on a consistent basis. 

Multi-stage anaerobic digestion can consistently achieve the required temperature for the prescribed 

time. Dewatering produces a Class A biosolids product as a “cake” consistency of 20% solids. This Class A 

cake is difficult to utilize because of its moisture content and is typically “bulked” by mixing with a 

chipped wood product to improve handling. 

Another approach to produce Class A Biosolids is through heat drying of the dewatered cake. When the 

heat drying process achieves the pathogen destruction temperatures, the product falls into the Class A 

Biosolids category. 

The heat dried product is typically 90% solids concentration and is granular in nature. It can easily be 

handled by individuals. For the purpose of the cost comparisons it has been assumed that no further offsite 

processing will be required for this product. Storage however, could lead to odour problems if 

moisture is allowed to re-hydrate the granules or pellets. 

The biosolids drying equipment will require fuel for heating the dryer and it has been assumed that 

propane or natural gas will be used. Fuel can also come from the methane gas produced by an anaerobic 

digestion it used ahead of the dewatering and drying process. The methane must be “scrubbed” prior to 

use as fuel for the dryer, in order to remove small particles, impurities and corrosive compounds. 

14.4 Class B Process Trains 

The production of a Class B Biosolids product at the Lot L site can be used as follows at a more remote 

site: 

 

 

Direct application to the mine reclamation project 

Potential composting to produce a Class B or Class A compost 

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The Sunshine Coast Regional District has expressed some interest in either a composting venture or 

production of a Biosolids Growing Medium project. A potential agreement could be worked out in the 

future, but for the purpose of the current cost comparisons, it is assumed that the current mine 

reclamation activities would continue. A dewatered Class B biosolids product will be produced at the Lot L 

site and trucked to the mine reclamation site for storage and seasonal use in the tree plantation. 

Three methods of producing a Class B biosolids product, dewatered to 18 - 20% solids concentration are 

costed and summarized in Appendix C. These are: 

1. Aerobic digestion plus dewatering 

2. Lime stabilization plus dewatering 

3. Thickening plus dewatering 

All of the above will produce a Class B Biosolids product. This will be hauled by truck to the mine 

reclamation site, stored, and used during the growing season to fertilize the tree plantation. 

14.5 Process Cost Summary 

Appendix C provides the capital cost estimates and annual operation and maintenance cost estimates for 

3 processes that yield Class B biosolids and 3 processes that yield Class A biosolids. These are 

summarized in Table 14.1. For5 a more complete description of the capital and operating cost estimates, 

refer to Appendix C. 

Table 14.1 - Cost Estimate Summary 

Class A Products 

Process 

Biosolids Solids Capital Cost Annual Total Present 

Class Conc. (%) $1,000’s O&M Cost Worth $1,000 

MS.Anaerobic + Dewater A 20-22% 6,294 196,000 8,737 

Thickening + Drying A 90-92% 5,400 130,000 7,020 

Digestion + Drying. A 90-92% 6,390 129,000 7,998 

Class B Products 

Process 

Biosolids Solids Capital Cost Annual Total Present 

Class Conc. (%) $1,000’s O&M Cost Worth $1,000 

Aerobic + Dewatering B 18-20% 4,227 180,600 6,478 

Lime Stab+Dewateriing B 20-22% 4,970 206,000 7,537 

Thick+Dewatering B 18-20% 3,814 169,600 5,928 

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Notes on Table 14.1: 

1. The Present Worth of the annual operation and maintenance costs is based on a 20 year term 

and a compound interest rate of 5%. The Present Worth Factor is 12.462. 

2. Dried product (greater than 90% solids content) would be hauled to the mine reclamation site at 

an annual cost of $5,000.00. This product can be made available to consumers, but no revenue 

has been included in the analysis. No application costs are included in these options. 

14.6 Discussion 

The cost analysis indicates that lowest Present Worth derives from thickening and dewatering to produce 

a Class B biosolids product that can be used in the tree planting operation. Using aerobic digestion to 

both thicken and reduce volatiles will also produce a Class B product and with less potential for odour 

formation. Both of these options are achievable within the current budget. The Class B biosolids can also 

be composted to produce a Class A compost, but at a more remote site, and preferably in conjunction 

with other partners. 

Production of a Class A biosolids product is most economical with thickening and heat drying. Class A 

biosolids from anaerobic digestion will require further drying by mixing with a bulking agent, air drying, 

and screening before it can be sold to consumers. 

Heat drying has the advantage of producing a Class A biosolids product that can be handled easily. With 

90% solids content, volumes are greatly reduced and hauling costs are minimized. Storage should be 

covered in order to prevent rehydration. 

With these assumptions the Present Worth of the thickening, dewatering and heat drying option is 

$7,020,000; or $542,000 higher than the aerobic digestion plus dewatering option. The initial capital cost, 

however is $5,400,000. With the addition of the estimated Ebb Tide plant improvements ($606,000.00) 

the project value is $5,006,000 or $1.2 million more than the current $4,800,000 budget. 

Page 53 

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APPENDIX A 

Environmental Screening 

Archaeological Assessment 

Geotechnical Assessment 

1592.0026.01 / December, 2010 




APPENDIX B 

Technical Memorandum #1 

1592.0026.01 / December, 2010 


REPORT 

Sechelt Sewage Facilities Commission 

Biosolids Technical Memorandum 

This report is prepared for the sole use of Sechelt Sewage 

Facilities Commission. No representations of any kind are 

made by Urban Systems Ltd. or its employees to any party 

with whom Urban Systems Ltd. does not have a contract. 

1592.0026.01 / July 19, 2010 

#304 - 1353 Ellis Street 

Kelowna BC V1Y 1Z9 

Telephone: 250-762-2517 

Fax: 250-763-5266



TABLE OF CONTENTS 

1.0 INTRODUCTION .................................................................................................................. 1 

2.0 THE ANDERCHEK SITE ........................................................................................................ 2 

3.0 BIOSOLIDS GENERATION .................................................................................................. 3 

4.0 THE OMRR (ORGANIC MATTER RECYCLING REGULATION) .............................................. 5 

5.0 THE CURRENT OPERATION ................................................................................................ 6 

6.0 DIVERTING BIOSOLIDS TO THE ANDERCHEK SITE ........................................................... 7 

7.0 TRUCKED WASTE OPTIONS ................................................................................................ 9 

8.0 BIOSOLIDS PROCESSING OPERATIONS ..........................................................................10 

9.0 FINAL PRODUCT CONSIDERATIONS ................................................................................13 

10.0 EBB TIDE IMPROVEMENTS ...............................................................................................15 

Page (i) 

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U:\Projects_KEL\1592\0026\01\R-Reports-Studies-Documents\Draft\2010-07-19-REP-Biosolids Technical Memorandum.doc



EXECUTIVE SUMMARY 

This is an Interim Technical Memorandum for the Sechelt Sewage Facilities Commission. It’s intent is to 

provide an overview of current sewage treatment operations and ideas for implementing a biosolids 

treatment facility. 

The first issue addressed is the method of diverting bio-solids from the two treatment plants to the 

proposed location of the new facility. The proposed location will ultimately see a full central treatment 

plant and an integration of sewage treatment and biosolids processing. In the meantime, however, the 

two existing plants will continue to function and a practical method of diverting sludge to the new site 

must be developed. 

The two options considered feasible are: 

 

 

Continue blending the Ebb Tide sludge with raw sewage and pump to the Dusty Road plant. 

Divert the Dusty Road sludge to the new site by constructing a new pipe on Dusty Road. This 

involves approximately 600 m of pipe installation. 

Re-direct Dusty Road effluent to another use such as gravel washing, or disposal to ground by 

rapid infiltration. This would free up the existing pipe for sludge transfer and both Dusty Road 

plant sludge and Ebb Tide plant sludge could easily be transferred to the new site. Removing 

Dusty Road effluent from the pipe system will also free up capacity in the Trail Bay outfall. This 

option will require discussion with CAL for the gravel washing opportunity and some 

hydrogeological investigation to find a site for rapid infiltration. Given the extent of gravel 

deposits in the area, a rapid infiltration site should not be difficult to find. 

The bio-solids treatment facilities will include digestion or thickening, depending on the end use and 

desired product. Dewatering is also included as it can expand the options available for re-use products 

and composting. A concurrent study is being undertaken to determine the optimum re-use opportunity. 

It is also recommended that consideration be given to a stand-alone treatment facility for trucked waste 

at the Dusty Road site in order to eliminate the risk of deleterious substances entering the biosolids 

treatment process. 

This interim paper also lists the current deficiencies at the Ebb Tide plant. Detailed costing for these 

items will be undertaken and priorities for implementation can be set out. 

Page (i) 

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1.0 INTRODUCTION 

The purpose of this Technical Memorandum is to provide the background and operating history of the 

Sechelt sewage treatment facilities, and the methods for dealing with biosolids. 

The approach taken is to examine the options available in the Sechelt area for the disposition or re-use of 

processed biosolids products and asses the processing required to achieve those products. 

The site being considered for processing is a site that was recently purchased by the District of Sechelt 

on lower Dusty Road, referred to as the Anderchek site. 

This Memorandum will also discuss the options for diverting biosolids to the Lot L site from both the Ebb 

Tide plant (ETP) and the Dusty Road plant (DRP). 

Page 1 

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2.0 THE ANDERCHEK SITE 

The Lot L site lies on the north side of Dusty Road approximately 100m east of the intersection with East 

Porpoise Bay Road. The site is 3.51 Hectares, with roughly 0.3 Hectare taken as a BC Hydro Right-of-Way 

(transmission line). The site varies in elevation from 40 m above mean sea level (ASL) to 28 m ASL. 

The comparative elevations of the three sites under consideration are: 

Dusty Road plant site: 112m ASL 

Lot L site: 40-28m ASL 

Ebb Tide plant site: 12m ASL 

The Lot L site is intended to ultimately accommodate the District’s central sewage treatment plant after 

the Dusty Road plant and the Ebb Tide plant are phased out; Dusty Road due to lease expiry and Ebb 

Tide due to age and inadequate site for expansion. 

Some preliminary assessments of the Anderchek site have been carried out. These include: 

 

 

 

Environmental Screening 

Archaeological Assessment 

Geotechnical Assessment 

Figure 1 shows the locations of the three sites. 

Page 2 

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3.0 BIOSOLIDS GENERATION 

Biosolids is the term used to refer to organic solids produced in the sewage treatment process. Biological 

treatment processes utilize a colony of active micro-organisms (biosolids) that consume incoming 

microbes and thereby reduce the level of pollutants. The colony is kept alive by the provision of oxygen 

and food. The “food” is the portion of removed biosolids that is returned to the colony. The other portion 

of removed biosolids is excess to the process and must be “wasted” or sent to a separate stream. The 

health of the colony is maintained by judicious recycle of biosolids in response to the incoming loads. 

The “waste” biosolids stream needs to be dealt with by other biological or physical chemical processes. 

Both the Ebb Tide plant (ETP) and the Dusty Road plant (DRP) produce biosolids that must be processed. 

The ETP does not have any biosolids processing facility. Excess biosolids at ETP are directed to the main 

lift station and blended with raw sewage to be pumped to the DRP. 

Consequently the DRP receives almost twice the solids loading as it would from typical raw sewage. The 

DRP handles biosolids in the conventional manner. A large portion of biosolids is returned to the bioreactor. 

The excess portion is sent to an on-site aerated pond. The aerated pond achieves a measure of 

stabilization, although this is not managed in any formal manner. 

The aerated pond also receives trucked waste or “septage”. Septage is the term used to refer to the 

sludge that accumulates and periodically gets pumped out of septic tanks. This material typically has a 

very high solids concentration and high oxygen demand. The contents of trucked waste are never known 

with certainty. While it can be assumed that it is mostly septage, operators are also engaged to pump out 

holding tank wastes from campgrounds and parks, catch basin sumps, car wash traps, agricultural 

dugouts, grease traps and a variety of other wastes. 

The impact of this additional load from trucked waste on the DRP has not been rigorously determined, 

but it does further increase the loading to the bio-reactor. It can also have a devastating impact if the 

trucked waste contains any material or chemicals toxic to the micro-organism colony. 

The aerated sludge pond overflows to an adjacent settling pond. This settling pond allows solids to settle 

and directs the surface decant water back to the plant bio-reactor. 

Accumulated biosolids in the settling pond are currently removed by tanker truck from May to October. 

The trucked material is used in reforestation sites in the discontinued gravel mining areas and used to 

support poplar tree growth. The operation is conducted by Sylvis Environmental Ltd. 

The typical volume hauled through the May-October season is 500 loads. The tanker truck volume is 8.2 

m 3 , so the total volume is 4100 m 3 per season. 

Page 3 

1592.0026.01 / July 19, 2010 




The hauled product meets the requirements of the BC Organic Matter Recycling Regulation (OMRR) for a 

“Class B” biosolids product. 

Figure 2 plots the recorded flows from 1984 to 2007. The rated capacities of the two plants are: 

Ebb Tide: 1700 m 3 /d 

Dusty Road: 2200 m 3 /d 

The solids loading to the Dusty Road plant is nearly twice that of normal design, since it receives the Ebb 

Tide sludge and trucked waste, so its operating capacity is more in the order of 1100 m 3 /d. 

Page 4 

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4.0 THE OMRR (ORGANIC MATTER RECYCLING REGULATION) 

The BC Organic Matter Recycling Regulation sets the standards for products which can be used in a 

variety of applications. These standards include parameters such as metals, moisture content, faecal 

coliforms and pathogens, foreign matter and a variety of other pollutants. The OMRR sets standards for 

recycled products under five classifications: 

 

 

 

 

 

Class B biosolids 

Class A biosolids 

Biosolids growing medium 

Class B compost 

Class A compost 

Class A compost can be used in all areas with unrestricted public access. The Biosolids growing medium 

can also be used with unrestricted public access. The other products have varying restrictions on use. 

The Class A products are typically subjected to temperatures in excess of 50 degrees Centigrade for a 

sufficient period to achieve pathogen die-off. 

A concurrent report is being undertaken, the “Biosolids Management Plan” which describes in more detail 

the provisions of the BC OMRR. 

Page 5 

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5.0 THE CURRENT OPERATION 

A schematic of the current plant configuration with respect to biosolids is provided on Figure 2. 

The main lift station at Ebb Tide receives both raw sewage (from an inlet splitting chamber) and waste 

sludge from the Ebb Tide plant. The waste biosolids are a mixture of primary clarifier sludge and 

secondary clarifier sludge. The plant does not meter or record the quantity of waste sludge. However, an 

approximation was made on a recent site visit and the amount estimated to be in the order of 30 m 3 /day. 

The main pump station pumps the blended material to the Dusty Road plant. The pump station utilizes 

tandem pumps to achieve the high lift required to get to the DRP (approximately 160 psi). The pipeline to 

DRP is approximately 2700m of 350 mm diameter forcemain. Due to poor installation, the pipeline has 

suffered leaks in several locations; some badly aligned joints can not support the high pressure. The 

problem was partly alleviated with the introduction of pump control valves in the station to reduce startup 

surges, and a check valve chamber at the foot of Dusty Road to reduce the risk of waterhammer. 

Nevertheless, the operator does not pump at full capacity for fear of potential joint failure. 

The pressure in the forcemain can be reduced by pumping to the Anderchek site (elevation 40 m) and repumping 

from there to the Dusty Road site. The first stretch would operate at 60 psi and the second at 

100 psi. These are more typical pressures for sewage forcemains. 

A parallel pipe is installed along the same route to carry treated effluent from the Dusty Road plant. This 

pipe joins the Ebb Tide effluent pipe, and the combined effluent flow is directed to the Trail Bay outfall. 

Effluent at the Dusty Road plant is chlorinated and the travel time in the pipeline is deemed sufficient for 

dechlorination. Effluent from the Ebb Tide plant is both chlorinated and dechlorinated, since the residual 

chlorine in the effluent is limited by the discharge permit. 

The relative distance of the two lines are: 

Ebb Tide plant to Lot L site: 2200 m 

Lot L site to Dusty Road plant: 600m. 

Figure 3 provides a schematic depiction of the interconnection between the two plants. 

Page 6 

1592.0026.01 / July 19, 2010 




6.0 DIVERTING BIOSOLIDS TO THE ANDERCHEK SITE 

a. Ebb Tide to Lot L 

Waste sludge from ETP can be transferred to the Lot L site by: 

 

 

 

A separate pump station and pipeline to the Lot L site 

Alternating pumping cycles through the existing forcemain 

Truck hauling 

The construction of a new forcemain from ETP to the Lot L site will incur considerable cost. Although the 

pipe size required is relatively small, construction on East Porpoise Bay Road will require significant 

reinstatement. Alternate routes may be available with less reinstatement costs, but this is not a cost 

effective option. 

Alternating pump cycles can be achieved with a PLC (Programmable Logic Controller) system. However, 

the amount of sludge required to purge the line on each cycle is in the order of 200 m 3 . This means that 

there must be about 6 day’s storage available at ETP. There is some volume within the plant tankage that 

could be used, but would not provide the 6 days of storage. This means additional storage would need to 

be built. This would also incur more cost. 

Hauling by septic truck can also be considered, but since each truck is roughly 8 m 3 , the number of loads 

would be approximately 5 loads per day. This also does not appear cost effective. 

A fourth option is to continue blending the biosolids with raw sewage and pump the mixture to the Dusty 

Road plant. The higher solids loading would be dealt with by modifications to the plant. 

A fifth option is to utilize the existing effluent line; this would require re-direction of the Dusty Road 

effluent. 

b. Dusty Road to Lot L site 

Waste sludge from the DRP can be directed by gravity to the Lot L site through the existing forcemain. 

This can be achieved by cycling the pump operation through a PLC. This strategy will also require purging 

of the main each time sludge is released. However, the volume in this portion of the pipeline is 56 m 3 , 

and storage is available in the existing aerated pond. 

Page 7 

1592.0026.01 / July 19, 2010 




A second option for DRP biosolids is to install a dedicated sludge pipe on Dusty Road down to the Lot L 

site. The length is 600m and the pipe size required is 150 mm diameter. 

A third option could utilize the existing effluent pipe. This would require finding some other destination 

for the DRP effluent. Options for reclamation include use as wash water for gravel washing operations, or 

use as irrigation water for the reforestation program. It may also be possible to develop a ground 

disposal system in an area that has significant gravel deposits. 

In summary, there are two basic options to explore in further detail: 

1. Continue blending ETP biosolids with raw sewage and process at the DRP. Divert the DRP waste 

biosolids to the Lot L site through a new dedicated sludge pipe on Dusty Road. 

2. Divert DRP effluent to the gravel washing facility and use the effluent pipe for sludge 

transmission for both DRP and ETP. 

Figures 4 and 5 provide schematic depictions of these two options. 

Page 8 

1592.0026.01 / July 19, 2010 




7.0 TRUCKED WASTE OPTIONS 

The following discusses three options for dealing with trucked waste: 

a. Construct a new receiving station for trucked waste at the Lot L site and process through 

the new biosolids facility. 

Comments: this option is feasible but incurs the risk of odours at the Lot L site. The process of unloading 

trucked waste generally results in release of odours as the septage is exposed to air. Because of its 

anaerobic condition. Trucked waste invariably contains non-degradable materials such as plastics and 

rubber. The receiving station should also provide for removal of these non-degradable materials. 

b. Retain the existing septage receiving station at Dusty Road and divert the sludge to the 

pipe leading to the Lot L site. 

Comments: this option achieves the same results as option (a) but retains the unloading operation at the 

Dusty Road site, where the is no nearby population and odours are not as great a concern. It also retains 

the use of the existing screening device for removal of inorganics. A new entry and charge card system 

will be required. When the lease expires, it may be feasible to retain a roadside turnout for the receiving 

station. In the long term, it is likely that as community sewer gets extended, the quantity of trucked 

waste will be reduced. 

c. Retain the existing receiving station and convert the existing ponds to a “stand-alone” 

septage treatment facility. 

Comments: this option has the advantage of keeping trucked waste entirely away from the main 

biosolids treatment facility. The risk of introduction of toxic or deleterious substances from trucked waste 

is thereby removed. Once biosolids from the Dusty Road plant have been redirected to the biosolids 

treatment facility, the existing ponds will become redundant. 

Page 9 

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8.0 BIOSOLIDS PROCESSING OPERATIONS 

Biosolids treatment can involve one or more unit processes, depending on the desired end product and 

its intended use. As previously stated the target can range from Class B biosolids to Class A compost. The 

basic processes in biosolids treatment can be classified into three basic functions. 

a. Stabilization processes 

Stabilization is achieved by “digestion”. Digestion converts the volatile fraction of solids into gas. 

Digestion can be anaerobic (no oxygen) or aerobic (with oxygen). Anaerobic digestion relies on heat to 

achieve the solid to gas conversion. The heat breaks down the volatile micro-organisms and the gas is 

released as methane and carbon dioxide, with traces of hydrogen sulphide. Anaerobic digester gas can 

have a strong odour. Containment of digester gas is recommended due to odours and explosion hazard. 

It is typically scrubbed and used in a boiler to generate heat for the digester; the excess is burned with 

flaring equipment. 

Aerobic digestion utilizes oxygen in the form of air diffusers to oxidize the volatile fraction of biosolids. In 

an aerobic environment, the gases produced are not odourous and can be released to atmosphere. No 

additional heat is required. Aerobically digested sludge is more difficult to dewater then anaerobic sludge. 

Autothermophilic digestion (ATAD) operates midway between aerobic and anaerobic digestion by 

maintaining a constant moderate temperature in the reactor. ATAD requires closer operator attention to 

ensure that conditions do not vary from the specified range. 

Other forms of stabilization involve chemical conditioning. Chemical conditioning may be applied to either 

raw or digested sludges. The chemicals used are typically polymeric coagulants and proper dosages 

result in rapidly settling flocs. For optimum performance, pH may need to be adjusted and this is usually 

achieved with the addition of “quicklime”. Quicklime is effective but very difficult to handle. Because of 

concerns with operator safety and the messiness of the lime slaking procedure, the popularity of 

quicklime has been decreasing. Other, more expensive, chemicals are used for pH adjustment if 

necessary. 

Page 10 

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b. Thickening 

Thickening is a concentration technique which is not intended to reduce volatile solids, but reduce the 

quantity of material to be handled. For example thickening a 1% solids concentration sludge to 5 % 

solids concentration reduces the volume to be handled by a factor of 5 times. If a dewatering process is 

involved, thickening makes dewatering more effective and reduces the size of the dewatering equipment. 

There are two widely used techniques for thickening: 

 

 

Gravity Thickening (GT) 

Dissolved Air Flotation (DAF) 

Gravity thickening functions much like a clarifier. Heavier solids are allowed to settle to the bottom of a 

quiescent vessel and withdrawn. A coagulant is usually added to enhance the settling process. Solids 

retention time in the vessel should be closely monitored to avoid anaerobic conditions and gasification. 

The power requirements for gravity thickening are minimal. 

Dissolved Air Flotation utilizes a stream of fine air bubbles to “float” the solids to the top of the vessel. 

These are then skimmed off for further processing. Dissolved Air Flotation has been very effective at 

thickening light sludges such as activated sludge. Both techniques can achieve a 4-5% solids 

concentration, but the DAF process requires more power for the diffused air supply. 

c. Dewatering 

Dewatering systems range from passive outdoor sludge drying beds to more sophisticated mechanical 

systems. Drying beds are not very effective in coastal climates, unless they are covered. Removal of 

dewatered sludge is labour intensive. 

The more common dewatering techniques currently in use are: 

 

 

Vacuum filters; these usually consist of a rotating drum with a fabric, plastic or wire mesh fine 

screen. The water is drawn through the screen by vacuum and the solids left behind are removed 

by a doctor blade on the drum. Polymer is added to improve the solid/liquid separation and a 

typical “cake” has a solids content ranging from 15 to 25%. 

Belt Filter Presses: these comprise a continuous belt which “squeezes” the water out of the 

sludge and the solids roll off the end of the belt. The power requirements are less than the 

vacuum filter, but the solids content of the dewatered product is less, varying from 10 to 15%. 

Page 11 

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Centrifuge: centrifuges are widely used for biosolids dewatering. Solid bowl centrifuges operate 

at high speeds and produce a high solids content cake (20 to 25%). This process is enclosed and 

the risk of odour less than with other dewatering processes. 

All of the foregoing techniques have a long history of usage in municipal applications. The liquid fraction 

that is separated is returned to the main plant bio-reactor. In this case it can be directed to the pump 

station which pumps raw sewage to the Dusty Road plant. When the central plant is eventually 

constructed, the liquid fraction will be directed back to the plant. 

d. Drying and Combustion 

Drying consists of dispersing the sludge in a stream of hot dry air and separating the dried solid in a 

cyclone. Other drying processes include Pyrolosis (a destructive distillation technique), cyclonic 

incinerators, electric infrared furnaces, fluidized bed incinerators, and multiple hearth incinerators. 

Drying processes result in over 80% solids content and the product is suitable for incineration or landfill 

disposal. 

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9.0 FINAL PRODUCT CONSIDERATIONS 

The final product targets should reflect the provisions of the OMRR if beneficial reclamation of organic 

biosolids is desired. The product can also be suitable for landfill cover material or incineration. Drying 

techniques can produce a very dry product that is suitable for incineration, but the process is very costly 

and not energy efficient. 

We have divided the potential targets into two classifications; 

a. Biosolids Classes (A, B or Growing Medium) 

The product currently being produced and being used by Sylvis for reforestation meets the parameters 

for Class B biosolids. The application in liquid form is sprayed from the back of the tanker between the 

rows of trees. This application technique has been approved by Ministry of Environment. The area is 

restricted to public access. 

The same process can be continued with properly digested sludge to reduce the vectoring and 

contamination risk. The hauling costs would be similar since digested sludge quantities would not be 

significantly less than the current volumes. Thickened sludge could also be used, and hauling costs would 

be reduce slightly is if a 5% solids concentration could be achieved. 

Dewatering would reduce the quantities by a factor of five, so the current 500 loads would reduce to 100 

loads. Sylvis has indicated that their application technique for dewatered biosolids (20% solids content) 

would change from the current, but the product could still be used for reforestation. They would also find 

it easier to stockpile the dewatered material. Stockpiling is necessary since the application rates do not 

match the sludge production rates. 

Dewatered sludge is also suitable for landfill cover material since it is not “runny” and application on 

slopes is feasible. A digested and dewatered sludge offers more options than a liquid sludge. 

b. Soil Amendment Products 

Soil amendment products will require composting. The composting process utilizes Nitrogen (from 

biosolids) and Carbon (from wood products). The OMRR recognizes Class A and Class B compost 

depending on the prior processing of biosolids and the retention time in the compost area. 

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A Class A compost is sufficiently dry and stabilized that it can be sold commercially as a soil amendment 

product for use on private property. The experience in the Okanagan and the lower mainland has been 

that the product is popular and sells well, but revenues are far below the cost of production. 

Composting requires: 

 

 

 

A strong commitment and partnership with other local governments to produce a desirable 

product. 

A large site, preferably remote from inhabited areas 

A reliable and inexpensive source of Carbon such as wood chips 

If partnerships do not emerge, the District can compost their own biosolids in limited quantities for use in 

parks and open spaces. However, the costs of small operations are usually prohibitive. 

Figure 6 provides a schematic depiction of the facility operation. 

Page 14 

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10.0 EBB TIDE IMPROVEMENTS 

A site visit was conducted on July 8 and July 9 , 2010. The operation and condition of a variety of plant 

component s were inspected and discussed with the operators. The following is a list of items to be 

repaired or replaced at the Ebb Tide plant. 

 

 

 

 

 

 

 

 

 

 

 

 

 

Water distribution lines (galvanized steel) of 25 and 50 mm diameter – badly rusted. 

Air lines (galvanizes steel) 50 mm diameter – badly rusted 

Explore feasibility of using effluent to supply the chlorinator (instead of municipal water) 

Replace the 100 mm diameter sludge air lift pipes 

Purchase and install a composite sampler (only grab samples are currently taken) 

Purchase and install an ultrasonic level monitor to re-activate the inlet Parshall flume flow 

recording 

Obtain pricing for a new bar screen and screening compactor. The existing bar screen has a 

limited remaining life, and purchase of a new screen will depend on the time allotted for 

decommissioning of the plant. 

Replace the clarifier gear drive 

Replace rusty handrails 

Install kick plates on all catwalks ( A WCB requirement) 

Replace the roof shingles on the plant superstructure. 

Install a floor drain and sump pump in the basement of the control building (emergency shower 

was installed recently to comply with WCB requirements, but there is no drain in the area). 

Chlorine automatic shut-off valves (WCB requirement) are being installed. 

Detailed cost estimates for the above items have not been completed and await supplier submissions. 

Once the costs are all in, a priority listing exercise should be undertaken, since the total cost may exceed 

the budget. Some of the items fall under the category of “required urgently” while othesr are “desired 

but not urgent”. 

Page 15 

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APPENDIX C 

Cost Estimates 

1592.0026.01 / December, 2010 


1.0 COST ESTIMATES 

1.1 Capital Cost Estimates 

Table presents approximate cost estimates for each of the process trains short listed 

Division 

Aerobic 

Digestion 

& Dewatering 

Lime 

Stabilization 

& Dewatering 

Gravity 

Thickening 

& Dewatering 

Multi-Stage 

Anaerobic 

Digestion & 

Dewatering 

Thickening, 

Dewatering 

and Heat 

Drying 

Single Stage 

Anaerobic 

Digestion, 

Dewatering 

and Heat 

Drying 

Div.1 – General Requirements $150,000 $150,000 $150,000 $200,000 $150,000 $250,000 

Div 2 – Site Works $530,000 $530,000 $400,000 $530,000 $400,000 $550,000 

Div 3 – Concrete $660,000 $680,000 $580,00 $650,000 $580,000 $600,000 

Div 4 – Masonry - - - 

Div 5 – Metals $68,000 $76,000 $60,000 $130,000 $60,000 $90,000 

Div 6 – Wood & Plastics $88,000 $98,000 $80,000 

Div 7 – Thermal & Moisture 

Protection 

$76,000 $86,000 $76,000 $90,000 $75,000 $90,000 

Div 8 – Doors & Windows $38,000 $48,000 $38,000 $38,000 $42,000 $48,000 

Div 9 – Finishes $42,000 $64,000 $42,000 $60,000 $48,000 $65,000 

Div 10 – Specialties (Odour Control) $80,000 $100,000 $90,000 $140,000 $100,000 $140,000 

Div 11 – Equipment & Installation $990,000 $1,400,000 $900,000 $2,300,000 $1,900,000 $2,200,000 

Div 12 – Furnishings $32,000 $42,000 $32,000 $42,000 $50,000 $50,000 

Div 13 – Special Construction - - - $40,000 $50,000 $80,000 

Div 14 – Conveying Systems $52,000 $52,000 $52,000 $52,000 $65,000 $65,000

Division 

Aerobic 

Digestion 

& Dewatering 

Lime 

Stabilization 

& Dewatering 

Gravity 

Thickening 

& Dewatering 

Multi-Stage 

Anaerobic 

Digestion & 

Dewatering 

Thickening, 

Dewatering 

and Heat 

Drying 

Single Stage 

Anaerobic 

Digestion, 

Dewatering 

and Heat 

Drying 

Div 15 – Mechanical $85,000 $95,000 $85,000 $110,000 $110,000 $125,000 

Div 16 – Electrical $240,000 $260,000 $240,000 $280,000 $370,000 $380,000 

Subtotal $3,131,000 $3,681,000 $2,825,000 $4,662,000 $4,000,000 $4,733,000 

Contingencies & Engineering (35%) $1,096,000 $1,289,000 $989,000 $1,632,000 $1,400,000 $1,657,000 

Total $4,227,000 $4,970,000 $3,814,000 $6,294,000 $5,400,000 $6,390,000 

Biosolids Product Class B Class B Class B Class A Class A Class A 

% Solids 18-20 20-22 18-20 20-22 90+ 90+

1.2 Operating Cost Estimates 

Table presents approximate operating cost estimates for each of the process trains short listed 

Item 

Aerobic 

Digestion & 

Dewatering 

Lime 

Stabilization & 

Dewatering 

Gravity 

Thickening & 

Dewatering 

Multi-Stage 

Anaerobic 

Digestion & 

Dewatering 

Thickening, 

Dewatering 

and Heat 

Drying 

Single Stage 

Anaerobic 

Digestion, 

Dewatering 

and Heat 

Drying 

Power $15,000 $6,000 $5,000 $7,000 $8,000 $9,000 

Fuel $12,000 $14,000 

Labour $26,000 $40,000 $26,000 $40,000 $32,000 $40,000 

Polymer $4,000 $4,000 $4,000 $4,000 $4,000 $4,000 

Lime $18,000 

Odour Control $12,000 $12,000 $12,000 $16,000 $16,000 $16,000 

Hauling $24,000 $24,000 $24,000 $24,000 $6,000 $6,000 

Maintenance $5,000 $5,000 $5,000 $7,000 $7,000 $7,000 

Parts Allowance $5,000 $5,000 $5,000 $7,000 $7,000 $7,000 

Testing/Reporting $5,000 $5,000 $5,000 $5,000 $5,000 $5,000 

Subtotal $96,000 $119,000 $86,000 $110,000 $97,000 $98,000 

Administration (10%) $9,6500 $12,000 $8,600 $11,000 $9,700 $9,800 

On Site Annual Costs $105,600 $131,000 $94,600 $121,000 $106,700 $107,000 

Off Site Annual Costs $75,000 $75,000 $75,000 $75,000 $5,000 $5,000 

TOTAL ANNUAL $180,000 $206,000 $169,600 $196,000 $111,700 $112,800 

Present Worth $2,251,000 $2,567,000 $2,114,000 $2,443,000 $1,392,000 $1,406,000



APPENDIX D 

Photos 

Phase 1 – Existing Aerated Biosolids Pond at Dusty Road Plant 

Phase 2 – Existing Settling Pond at Dusty Road Plant 

Phase 3 – Growing Medium stockpile at Sylvis Site 

Phase 5 – Lot L looking North from Dusty Road 

Phase 6 – Lot L looking South from Allen Road 

1592.0026.01 / December, 2010

District of Sechelt Preliminary Report

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