Waste to Energy: Harnessing the fuel in organic waste to create a business opportunity for a recycling-based society and system

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To generate a feasible amount of methane to support a digester, it is estimated that 10 to 12 tons/d, with 8-10% contamination and 80% of the contamination being bioplastics, can produce about 70 Nm3/h of biogas. This is the amount of biogas needed to produce 200 kg/day of hydrogen, which is the smallest commercially available packaged system. The greenhouse gas emission (GHG) for IngeoTM is currently 1.3 kg CO2 eq./kg polymer compared to approx. 3.2 kg CO2 eq./kg polymer for PET. Therefore, implementing anaerobic digestion for PLA can reduce around 942.5 kg - 1132 kg per day of CO2 equivalent emissions.

A total of 1 ton per day of undigested bioplastic with 30% of total solids will be sent to landfills; 3 tons per day of dewatered digestate cake can be utilized for composting, and Class A fertilizer can be produced. The research on anaerobic degradation of biopolymers is still in its infancy. Therefore, this report has discussed different pre-treatment alternatives to treat PLA such as physical, chemical, and thermal treatments. This report suggests on-site segregation benefits of the current solid waste management scenario in the commercial sector of Plano, Texas. Organic waste generated from a cafeteria of the commercial sector in Plano caused an environmental impact on landfills. This report consists of a description of existing scenarios and possible pre-treatment alternatives for bioplastic degradation generated from the commercial sector.

Harshada Pednekar was a graduate research analyst in the Hunt Institute while studying for a masters degree in environmental engineering from SMU's Lyle School of Engineering

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Waste to Energy:

Harnessing the fuel in organic waste

to create a business opportunity for a recycling-based

society and system

Industry Advisors:

Terra Group at the Toyota Motor North America

Matthew Sheldon, Social Intrapreneur

Jason S Sekhon, Fuel Cell and Hydrogen SME

Mark Hitchock, Zero waste, recycling, and the City of Plano Liaison

Kelli Gregory, NTCOG liaison, clean energy mobility

Graduate Research Analyst:

Harshada Pednekar

Project Manager:

Corrie A. Harris, MA, MBA

Faculty Advisors:

Mohammad Khodayar, Ph.D. Associate Professor in the

Department of Electrical and Computer Engineering at Lyle School of Engineering

Eva Csaky, Ph.D., Executive Director of the Hunt Institute

Southern Methodist University

Lyle School of Engineering

Hunter and Stephanie Hunt Institute for Engineering and Humanity

Global Development Lab

April 2021

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Table of Contents

SUMMARY 5

BACKGROUND 6

CORPORATE SOLID WASTE MANAGEMENT 8

AVAILABLE SOLUTIONS 9

RECYCLING/REUSE 9

INCINERATION WITH ENERGY RECOVERY 10

AEROBIC COMPOSTING 10

ANAEROBIC DIGESTION 11

Processes in the Digester 12

Digestate 15

Gas Production 15

LANDFILL 17

FEEDSTOCK COMPOSITION 18

THE RATIO OF FOOD WASTE TO PLA 18

ALTERNATIVES FOR PRE-TREATMENT OF PLA 18

PHYSICAL TREATMENT - REDUCTION IN PARTICLE SIZE & CHOPPING AND SHREDDING 19

CHEMICAL TREATMENT - ALKALINITY TREATMENT 19

THERMAL TREATMENT 20

ULTRAVIOLET IRRADIATION 21

DAIRY & WASTEWATER INOCULATION 21

NEED FOR AN ACCELERATING AGENT (I.E. GBX) 22

FEEDSTOCK QUANTITY, METHANE AND HYDROGEN PRODUCTION 23

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CONSISTENCY OF WASTE FROM EMPLOYER 24

RECOMMENDATIONS & WORKPLACE PRACTICES 24

CONCLUSION 25

FUTURE SCOPE 26

APPENDIX A 28

WORKS CITED 29

Useful Websites: 31

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Table of Figures

FIGURE 1: EXAMPLES OF PLA PRODUCTS - WORLD CENTRIC CUP, CUTLERY & CHIPS BAG (CALIFORNIA ORGANICS RECYCLING COUNCIL) .. 6

FIGURE 2: LIFE CYCLE OF BIODEGRADABLE PLASTIC DISPOSAL ..................................................................................................... 9

FIGURE 3: BIODEGRADATION OF BIOPOLYMERS: AEROBIC VS. ANAEROBIC DEGRADATION (BATORI ET AL. 2018)................................ 11

FIGURE 4: PROCESS FLOW DIAGRAM USED WITH PERMISSION BY JOHN MCNAMARA, VP AT CR&R ENVIRONMENTAL SERVICES ............ 12

FIGURE 5: PLA AT DIFFERENT DEGRADATION TIMES (A & B AT 0 DAYS, C & D AT 30 DAYS) (MOON ET AL. 2016) .............................. 14

FIGURE 6: CO2 GENERATION FROM DIFFERENT ORGANIC WASTE TREATMENTS (UNION OF CONCERNED SCIENTISTS) ......................... 16

FIGURE 7: COMPARISON OF UNTREATED CRYSTALLINE PLA BEFORE AND AFTER BMP TEST ........................................................... 20

FIGURE 8: MINERALIZATION OF PLA IN ANAEROBIC CONDITION AT 37C & 52C (ITAVAARA ET AL. 2002) ......................................... 21

FIGURE 9: SCHEMATIC DIAGRAM OF PLA DEGRADATION AND SOIL BURIAL ................................................................................. 22

FIGURE 10: BIOBASED PRODUCT LABELS, CALIFORNIA ORGANICS RECYCLING COUNCIL .................................................................. 24

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Summary

To generate a feasible amount of methane to support a digester, it is estimated that 10 to

12 tons/d, with 8-10% contamination and 80% of the contamination being bioplastics, can

produce about 70 Nm3/h of biogas. This is the amount of biogas needed to produce 200

kg/day of hydrogen, which is the smallest commercially available packaged system. The

greenhouse gas emission (GHG) for Ingeo TM is currently 1.3 kg CO2 eq./kg polymer

compared to approx. 3.2 kg CO2 eq./kg polymer for PET. Therefore, implementing

anaerobic digestion for PLA can reduce around 942.5 kg - 1132 kg per day of CO2

equivalent emissions.

A total of 1 ton per day of undigested bioplastic with 30% of total solids will be sent to

landfills; 3 tons per day of dewatered digestate cake can be utilized for composting, and

Class A fertilizer can be produced. The research on anaerobic degradation of biopolymers

is still in its infancy. Therefore, this report has discussed different pre-treatment

alternatives to treat PLA such as physical, chemical, and thermal treatments. This report

suggests on-site segregation benefits of the current solid waste management scenario in

the commercial sector of Plano, Texas. Organic waste generated from a cafeteria of the

commercial sector in Plano caused an environmental impact on landfills. This report

consists of a description of existing scenarios and possible pre-treatment alternatives for

bioplastic degradation generated from the commercial sector.

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Background

Bioplastic waste going to the landfill from break rooms and cafeterias of the commercial

sector in Plano has caused increasing environmental concerns for sustainability

professionals in the area. Diverting waste from landfills to decrease environmental impact

is a shared goal among corporations including Toyota Motor North America, Frito-Lay,

PepsiCo, and many others. Among the Environmental Challenge 2050 goals of Toyota is

a call to action to ensure that its facilities and processes support and establish a recyclingbased

society.

Recently, corporations in Plano switched all single-use items, including packaging, to

compostable plastics. Among the other materials, a wide range of Poly Lactic Acid (PLA)

products are currently used for cutlery (examples shown in Figure 1). Waste reduction at

the source is an effective practice that will divert waste from landfills and ultimately reduce

GHG emissions, ultimately leading towards achieving a zero-waste policy. Currently,

corporate waste management offerings in the Plano area cannot support zero-waste

goals. Companies are committed, however, to working with municipalities and other

concerned corporations to discover a path toward zero waste.

Figure 1: Examples of PLA Products - World Centric Cup, cutlery & chips bag (California Organics Recycling Council)

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The purpose of this engagement is to study and recommend potential solutions focusing

on an anaerobic digester, or other applicable technologies, as a potential solution to the

accumulation of Plano’s bioplastic waste ending up in landfills. The aim is to build broad

corporate support in the surrounding area for implementation by demonstrating the

potential greenhouse gas reduction, waste stream diversion from landfills, economic

value, and potential to create a future fueling source enabling consumers to purchase

and drive hydrogen-powered vehicles.

This report will thoroughly review the biodegradability of PLA. PLA & food waste have

complementary characteristics for anaerobic digestion; both are organic and degrade

under anaerobic conditions. Food waste and PLA are explored as potential energy

sources, while also examining the potential challenges that can occur while treating them

together. Currently, the worldwide annual production capacity for biodegradable plastic is

350,000 tons, which pales in comparison to that of conventional plastic, which is

estimated at 260 million tons (Miller 2005). However, the production of bioplastic has

reached an industrial scale, and awareness of its environmental benefits has increased.

In this report, various pre-treatments for the slow hydrolysis of PLA will be examined, and

feedstock capacity in the area will be evaluated to calculate minimum requirements. The

DFW Metroplex does not currently have a facility with an anaerobic digester for

commercial solid waste. Instead, this report’s evaluations and comparisons will be derived

from other locations, primarily in California.

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Corporate Solid Waste Management

The City of Plano has approximately 40 more years of landfill capacity. Currently, 149

pounds of trash per residential customer go to the landfill each month. There are two

transfer stations in Plano 1 . Trash loads are dumped at the local transfer stations then

transferred into larger trucks and hauled to the landfill. The average tipping fee is $43.35

per ton.

Texas Pure in North Texas produces compost, planting mix for gardening, and natural

and colonized mulch. Texas Pure accepts only food waste and yard debris. If there is

trash (plastic, metal, glass, waxy containers, compostable products) in the load, the trash,

or even the whole load, will be placed in the landfill. Food waste is not accepted at the

Plano location of Texas Pure, so it must be delivered directly to the Texas Pure site on

landfill property in Melissa, Texas. The North Texas Municipal Water District (NTMWD)

Landfill takes all items that residents put in their trash carts. They do not accept hazardous

material or construction site debris.

The City of Plano managed a food waste recycling program for approximately 40

businesses utilizing 95-gallon carts. Although the program was discontinued in February

of 2020, there are still several businesses in Plano that recycle food waste using other

haulers, namely: Sprouts, North Texas Food Bank, Whole Foods, Maui Foods, and Frito-

Lay. Texas Pure continues to process food waste from Whole Foods, Maui Foods, and

the North Texas Food Bank. Organizations rely on permitted haulers to collect and

transport their food waste to an authorized receiver or compost facility. A few of the larger

1 For more information about the transfer stations in Plano see https://www.ntmwd.com/facilities/

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commercial businesses keep recycling food waste through smaller independent food

waste recyclers like Organix. Organix hauls food waste from three Sam’s Club locations

and six Walmart and Sprouts locations.

Available Solutions

The life cycle of biodegradable plastic is shown in Figure 2, which includes typical

treatment options such as recycling (reprocessing polymer with debasing of properties),

monomer recovery (recovery of lactic acid from PLA), incineration with energy recovery,

composting, anaerobic digestion, and landfill. The next section will describe each of these

alternatives.

Recycling/Reuse

Figure 2: Life Cycle of Biodegradable Plastic Disposal

Any plastic, whether conventional or bio-based, that enters the municipal waste stream

causes complications. Although it is feasible to mechanically recycle some bioplastic

polymers, such as PLA, a few times without significant reduction in properties, the lack of

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continuous and reliable supply of bioplastic polymer waste in large quantities presently

makes recycling less economically attractive than for conventional plastics. The “4R’s”—

reusing, reducing, recycling, and repurposing—when compared to traditional waste

management practices, offer a more effective answer to the ongoing bioplastic waste

disposal dilemma.

Incineration with Energy Recovery

Most commodity plastics have gross calorific values (GCV) comparable to or greater than

that of coal (Davis & Song 2006). Incineration with energy recovery can be a good option

for all recyclable waste, but it also has an adverse impact. In addition to the toxic gases

generated from incineration, the installation of an incineration plant is an expensive

process requiring trained personnel and frequent maintenance. In the case of bioplastic,

the GCV of both natural cellulose and fiber starch is lower than that of coal but comparable

to that of wood, and they therefore have considerable value for incineration.

Aerobic Composting

Unlike petrochemical polymers, PLA can be composted, generating carbon and nutrientrich

compost. Not all bio-based products are compostable or biodegradable and vice

versa. Biodegradation of organic material, including bioplastic, produces valuable

compost along with water, CO2, and heat. However, the produced CO2 does not contribute

to an increase in greenhouse gases, as it already exists in the biological carbon cycle

(Song, et al. 2009).

According to estimation from Anargia, a ton of the organic fraction of municipal solid waste

sent to composting produces approximately +80 kg of CO2 equivalent (eq). PLA alone did

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not biodegrade at mesophilic temperature (25-60°C), and only 10% CO2 was generated

within 210 days. In contrast, the highest rate of CO2 occurred at 60°C, reaching

mineralization of 90% within 120 days and 40 days of lag time observed. (Itavaara et al.

2002) Less than 10% mass retained by a 2mm sieve and resultant compost has no

adverse impact on plants (OECD 2008). Standard tests are available for evaluating the

compostability of biopolymers, such as ASTM D6400 and ISO17088.

Anaerobic Digestion

In anaerobic degradation (AD) of biopolymers, the energy is stored in organic matter and

is released as methane. Due to the lack of oxygen in this process, less heat and less

microbial mass are produced. However, during the aerobic process the energy in organic

matter is released as heat and cannot be captured. Figure 3 shows a diagram of the

biodegradation of biopolymers and compares aerobic and anaerobic degradation. The

dark green symbols represent the microorganisms involved in the processes. (Batori, et

al. 2018)

Figure 3: Biodegradation of Biopolymers: Aerobic vs. Anaerobic Degradation (Batori et al. 2018)

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In the last decade, numerous studies have focused on the PLA degradation under various

treatment conditions such as hydrolysis, hydrothermal, and compost. Compared to

mesophilic (37°C) processes, thermophilic (55°C) and hyperthermophilic (above 55°C)

AD processes have the advantage of more effective organic particle stabilization and

higher biogas production (Nielsen & Petersen 2000). However, generally applicable and

effective methods for PLA have not yet been proposed (Wang, et al. 2012). Figure 4

describes the typical process of anaerobic digestion of organic waste.

Figure 4: Process flow diagram used with permission by John McNamara, VP at CR&R Environmental Services

Processes in the Digester

The two-stage, up-flow anaerobic sludge blanket (UASB) reactor is a suitable (good

mixing) technology for high strength waste (>15% solids) from the commercial sector

(Schroepher, et al. 1955). PLA is a high molecular weight polymer, and very few

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microorganisms like Stenotrophomonas pavanii and Pseudomonas geniculata can

colonize and degrade it. These are examples of nitrogen-fixing, gram-negative

microorganisms. It has been observed that PLA is, despite the presence of various

polyester-degrading microorganisms, very slowly degraded. PLA undergoes chain

scission to fragments and oligomers, hence requiring extensive hydrolysis before the

biotic attack. PLA can form a highly crystalline structure that is more difficult to hydrolyze

than amorphous (Reeve, et al. 1994). ASTM Method D5511 is a standard test method for

determining anaerobic biodegradation of plastic material under high-solid anaerobic

digestion conditions.

Necessary pre-treatments are explained later in this report. In thermophilic conditions,

anaerobic biodegradation of PLA is faster than in aerobic conditions due to lactic acid

being a more favorable substrate for anaerobic than aerobic microorganisms. At high

temperatures, micro molecular structure changes, and Siparsky et al. (1997) find that

water absorption into the polymer matrix increases. This not only accelerates the

chemical hydrolysis, but it also increases polymer hydrophilicity which makes it more

accessible to microbes and enzymes (Karjomaa, et al. 1998). Therefore, higher

biodegradation is measured at higher temperatures—about 90% biodegradation of PLA

in 60 days at 55°C with no lag phase observed (Yagi, et al. 2009). These results are

achieved from an evolved system developed by using a gas collection bag at atmospheric

pressure.

The morphological characteristics of the PLA particles were examined under optical

microscopy. Figure 5 shows the bacterial attachment on the PLA surface. For this

experiment, only the bacteria with the ability to attach to PLA were selected and those

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bacteria were dominant in the final stage (c & d) of degradation as shown in Figure 5

(Moon, et al. 2016). Additional research will be needed to examine the metabolic

reactions at the interface.

Figure 5: PLA at Different Degradation Times (a & b at 0 days, c & d at 30 days) (Moon et al. 2016)

Important parameters in the AD processes are – Solid Retention Time, Hydraulic

Retention Time, temperature, pH, alkalinity, moisture content, C/N (carbon/nitrogen) ratio,

nutrients, and toxic material. SRT is the average time the solids are in the system, and

HRT is a measure of the average length of time that water remains in a bioreactor. SRT,

HRT, and temperature are required to determine the processes, while alkalinity controls

the digestion, and nutrients and toxic material determine bacterial growth. Most

bioplastics are very carbon-rich and contain little to no nitrogen; the addition of bioplastics

to corporate cafeteria organic waste, however, will improve the C/N ratio of the mixture.

ADs are highly susceptible to upsets due to environmental conditions such as weather

and seasonal variation. Therefore, it is crucial to maintain the parameter within the

recommended limit. Appendix A shows the specifications of the AD process for Food

Waste and PLA (Tchobanoglous 2014).

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Digestate

Ideally, bioplastics would biodegrade and disintegrate during the anaerobic phase in an

anaerobic digestion plant, just as a major part of “natural” biowaste does. However, if

bioplastics disintegrate during the anaerobic phase, they later can biodegrade completely

during the aerobic stabilization phase or with the use of digestate or compost in the soil.

Usually, industrial digestate is sieved through a 2 mm mesh, and if the resulting biomanure

is not 100% PLA, it can be dangerous. The feedstock of pure PLA can produce

Class A sludge and be used as fertilizer on farms.

No significant amount of chemicals (PLA, Accelerant, etc) were found in the composting

process, but daily lab testing is required. Seasonal variation in the waste can create

obstacles in the process. A sampling at various stages is recommended. The undigested

matter would go to the landfill, and it is assumed that the residual untreated PLA from the

AD process will not continue to emit biogas when landfilled and will offset emission via

carbon sequestration. Generally, one ton per day of organic matter produces

approximately 33 tons of bio manure per year.

A total of 1TPD of undigested bioplastic with 30% of total solids will be sent to the

landfill; about 3TPD dewatered digestate cake can be utilized for composting, and

Class A fertilizer can be produced.

Gas Production

Gas from anaerobic digestion contains about 65 - 70% CH4 by volume, 25 to 30% CO2,

and small amounts of N2, H2, H2S, water vapor, and other gases. PLA was degraded

using dry digestion with high solids under the mesophilic condition up to 60% over 40

days (Itavaara, et al. 2002). It was found that approx. 90% degradation occurs in 60 days

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under 55°C (Yagi, et al. 2009) whereas 189 N-Lit/dry kg of methane estimated from 40%

degradation of amorphous PLA at 35°C for 170 days (100% degradation gives 467 N-

Lit/dry kg based on reaction – C6H8O4 + 2H2O → 3CO2 + 3CH4) (Kolstad, et. al. 2012).

For this particular scenario for a single corporation, 10 TPD of food and bioplastic waste

with 28% of total solids would produce 66 N-m3/hr of biogas under the mesophilic

condition with HRT of 24 days and an organic loading rate of 4.3 kg VSS/m3.d in insulated

bolter steel anaerobic digester. After biogas conditioning, 40 N-m3/hr of biomethane will

be generated.

Landfill biogas has a greater carbon intensity than digester biogas because landfill

systems are not as efficient at producing and capturing biogas, whereas digesters are

specifically designed for that purpose. Figure 6 shows that organic diversion and

anaerobic digestion can result in negative lifecycle emissions (Union of Concerned

Scientists 2012).

Figure 6: CO2 Generation from Different Organic Waste Treatments (Union of Concerned Scientists)

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Landfill

Waste plastics being sent to landfill is the least favored option in the waste hierarchy.

Levels of concern are rising for the impact of landfills on health and the environment due

to the number of toxic materials in land-filled municipal waste and their potential leaching

out of landfill sites. The landfill of biodegradable materials including bioplastic polymers,

garden waste, and kitchen waste presents a problem in that methane, a greenhouse gas

with 25 to 36 times the effect of CO2, may be produced under anaerobic conditions

encountered in the landfill. In the US, a typical recycling facility is not equipped to deal

with food packaging, and this material is therefore disposed of in landfills.

The assessment of anaerobic degradation of Ingeo TM PLA under accelerated landfill

conditions shows that semi-crystalline PLA under AD in a landfill at a moderate

temperature will not generate significant methane because there are no significant

microorganisms available to degrade high molecular weight PLA. Therefore, it needs a

chemical hydrolysis step before any degradation (Kolstad, et al. 2012).

Fortunately, methane is an energy-dense fuel that can be used for electricity, heating,

and transportation. For example, U.S. waste-derived “biomethane” could produce nearly

4.5 billion gasoline-equivalent gallons of fuel annually—enough fuel for 10.4 million cars

(EIA 2021). This could displace nearly 75% of the natural gas consumed by the

transportation sector or 7% of the natural gas consumed by the electricity sector (EIA

2021). As the electric vehicle market continues to grow, biomethane-generated electricity

could allow for truly zero-emission driving.

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Feedstock Composition

Food waste has a high energy potential and an estimated decay rate of 0.14 yr - which

makes it compatible to digest with PLA. Feedstock will be composed of food waste and

PLA/bioplastic. The source of food waste is the cafeteria and canteen food waste.

Because of high moisture content (approx. 80% or more) in food waste, it is suitable to

combine with PLAs that are low in moisture content. Not all bio-based plastics will

biodegrade. Lactic acid is a great source of food for microorganisms and hence is easy

to biodegrade. Biodegradable bioplastics like pure PLA have great potential to contribute

to material recovery, reduction of landfills, and use of renewable resources.

The Ratio of Food Waste to PLA

There are a variety of ratios of food waste to PLA recommended, but overall, a very small

percentage of PLA to organic waste is feasible. The ratio of bioplastic to kitchen waste

was kept very low at a compost plant in Kassel, Germany: 1 plastic part to 99 parts of

organic waste on a weight basis. It showed no negative effects observed in terms of

quality and the same effect on plants as regular compost. (Song, et al. 2009). SMU faculty

members from the Civil and Environmental Engineering Department and professionals

had the same opinion that an acceptable ratio is up to 10%. It can also work as COD of

kitchen garbage (raw - 230 g/lit) to PLA at a 4:1 ratio. (Wang, et al. 2012).

Alternatives for Pre-Treatment of PLA

Inconsistencies in product labeling and a lack of accepted definitions for industry terms

confuse consumers upon purchasing and discarding products. Improperly sorted

bioplastics can contaminate recycling streams and feedstock for composting operations

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or end up buried in a landfill. Also, inconsistent rates of decomposition across products

can impede commercial composting operations.

Physical Treatment - Reduction in Particle Size & Chopping and

Shredding

Particle size may significantly affect the speed and stability of anaerobic digestion, so

matching the choice of particle size reduction equipment to digester type can determine

the outcome of the process. The anaerobic biodegradation rate of PLA film (thickness 25

μm) was faster than the PLA powder (125–250 μm) at 55 °C. Itavarra, et al. (2002) found

that samples of 2x2 cm pieces of PLA film diluted in wastewater inoculum had better

degradation due to the physical change of the PLA. On the contrary, although the smaller

pieces were expected to degrade faster, it turned out that they stuck together and

generated static electricity. Therefore, the total surface area in contact with sludge was

less than with larger pieces (Batori, et al. 2018).

Chemical Treatment - Alkalinity Treatment

Alkaline pretreatment has the highest solid reduction rate of PLA and maximum

production of CH4 when combined with food waste and anaerobically digested sludge.

PLA dissolving in a high alkaline solution leads to hydrolysis of aliphatic polyester,

cleaving the ester bonds. The hydrolytic degradation of crystalline PLA leads to an

increased rate of mass loss in solution and increased consumption of O2 due to PLA

content. The biotic degradation of PLA is desirable during disposal, and degradation can

be enhanced through thermal treatment making anaerobic digestion viable. Hobbs, et al.

(2019) found that PLA incubated at 12.96 pH for 15 days showed 98% solubilization.

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Figure 7: Comparison of Untreated Crystalline PLA Before and After BMP Test

Figure 7 shows the change in the weight of PLA. The PLA without treatment after

anaerobic digestion experienced a 53% reduction of initial weight due to the conversion

of long polymer chains into shorter chains under alkaline treatment.

Thermal Treatment

Despite the biocompatible nature of bioplastics, the degradation of PLA in the

environment is not easy because, under ambient conditions, PLA in soil or sewage is

resistant to microbial attack. Thermophilic (50-60°C) systems have a faster throughput

with faster biogas production per unit of feedstock and digester volume. However, the

capital costs of thermophilic systems are far higher, more energy is needed to heat them,

and they generally require more management.

Figure 8 indicates that 60% mineralization of PLA took place in anaerobic aquatic

conditions at 37°C in 100 days, while at 52 o C, 60% was mineralized in 40 days. This

shows that thermophilic temperature is the key parameter affecting the biodegradation

rate of PLA.

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Figure 8: Mineralization of PLA in Anaerobic condition at 37C & 52C (Itavaara et al. 2002)

Ultraviolet Irradiation

Ultraviolet irradiation at a wavelength of 254 mm (UV-C) can break the long chains of PLA

beverage cups and reduce the average molecular weight (Jeon & Kim 2013). The

exposure of PLA waste to UV-C radiation before composting will increase the rate of PLA

degradation.

Dairy & Wastewater Inoculation

Anaerobic microbial inoculum was derived from an anaerobic wastewater treatment

facility, and that dairy manure can be used for testing of PLA degradation. The dairy

wastewater sludge was Actinomadura, a good source of microbial consortia. The amount

of inoculum was equivalent to 10% of the volume of the solution. Figure 9 shows a

schematic diagram of PLA degradation under UV-C irradiation followed by Soil Burial,

Dairy Wastewater Sludge (DWS), and P. geniculate WS3 additions

(Pattanasuttichonlakul 2018). UV-C irradiation decreased the molecular weight of PLA

as compared to UV-A and UV-B.

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Figure 9: Schematic Diagram of PLA Degradation and Soil Burial

UV-C-treated PLA sheets are buried in the soil with DWS and P. geniculata WS3

additions. P. geniculata WS3 and some microorganisms in DWS, adhered to the PLA

surface, excreted PLA-degrading enzymes. The PLA-degrading enzyme is absorbed or

localized on the PLA surface (Bubpachat et al., 2018). The PLA degradation process

involves chemical and enzymatic hydrolysis. Qi, et al. (2017) recommend the process of

UV-C irradiation and the addition of DWS and P. geniculata WS3, as these offer an

efficient method for accelerating PLA degradation under aerobic soil burial conditions.

Need for an Accelerating Agent (i.e. GBX)

There is no need to add an accelerating agent for PLA & food waste feedstock. If any

specific kind of industrial waste is treated, then it may need an accelerating agent, such

as Inoculum from WWTP or dairy. This report recommends running the process as

naturally as possible.

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Feedstock Quantity, Methane and Hydrogen

Production

It is estimated that 10 to 12 tons/d (one collection compactor truck) of food waste with 8

to 10% contamination (wet/wet basis) and 80% of the contamination being bioplastics

(the rest conventional plastics and others) can produce about 70 Nm3/h of biogas. This

is the amount of biogas needed to produce 200 kg/day of hydrogen. The focus is on 200

kg of H2 because this is the smallest size of commercially available packaged and

containerized biomethane reforming systems. The design parameters for AD are as

follows: HRT of 24days, digester volume of 500 m 3 , and organic loading rate of 4.3 kg

VSS/m 3 per day. (Anargia)

There is another design approach for small-scale distribution facilities that would produce

100 to 1500 kg of hydrogen per day at fueling stations. For 200 kg per day of hydrogen,

the biogas flow rate should be 120 cfm at 60% methane (172,000 cuft per day). To

produce that amount of biogas, the digester’s organic loading would need to be 28,800

lbs per day of COD (based on ~6 cubic feet per lbs of COD). Food waste and 10% PLA

must blend and make a slurry (feed material blend) with 100,000 mg/L COD or 35,000

gallons of feed material (attached biogas yields). SMR Technology is widely used to

generate hydrogen because of its performance and cost-efficiency (Tasser).

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Consistency of Waste from Employer

Figure 10: Biobased Product Labels, California Organics Recycling Council

● Reduction and Segregation at source by placing color-coded bins

● Connect with restaurants, supermarkets, or food & PLA-generating commercial

sectors

● Implementing effective biological treatment for the developing range of PLAs will

require clear certification and labeling schemes

● An effective collection system should accept only 100% biodegradable products

(not all biobased products are biodegradable; Figure 10 shows the widely

recognized labels which demonstrate compliance with ASTM D6400 & ASTM

D6866, respectively)

● Tipping fees - The best practice of establishing long-term off-take contracts are

with guarantees for quantity and composition to secure project financing

Recommendations & Workplace Practices

● Buy products from certified 100% pure PLA products e.g. Ingeo, Nature Works,

and ask them for certification of 100% biodegradation

● Separation of waste in different bins for different kinds of waste, such as

recyclable, landfill, organic wet, organic dry, and PLA (used spoons, dishes, and

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other cutlery) with the list of materials or photographs to identify appropriate waste

placement

● Spread awareness on the benefits of waste separation - reduces cost, treatment,

energy, and labor

Conclusion

The purpose of this project is to study and recommend potential solutions through an

analysis of corporate waste management options in Plano, Texas, focusing on an

anaerobic digester or other applicable technologies to be used for several possible

benefits: greenhouse gas reduction, diversion from landfill, economic value, and the

potential to create a fueling source for hydrogen-powered vehicles.

The minimum requirements of feedstock for a digester are 10 tons a day equating to

~3650 tons of feedstock annually. If one corporation produces 1.5 million lbs (769 tons)

annually leaving a deficit of 3650 tons and the City of Plano collects approximately 30,000

tons of yard waste annually with a breakdown of 1,915 tons a month, a partnership with

the City of Plano would guarantee the minimum feedstock to sustain the anaerobic activity

of bacteria and the production of methane gas to meet the energy needs of the plant.

Securing a reliable feedstock supply is fundamental to profitable AD and if feedstocks are

to be bought from a third party, securing a long-term contract on acceptable terms is

critical. Partnerships with other corporations’ supplies of feedstock would be beneficial for

the environment and establishment of challenges like recycling-based society and

systems for Plano, TX. However, the risk associated with wet organic waste quality from

corporations would not be reliable to run a digester constantly throughout the year.

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Additional partnerships are advisable based on the business model for CR&R, Inc. The

success of this endeavor would increase with industry partners who specialize in

anaerobic digestion technology maintenance like Esenmann, biogas upgrading

technology like Greenlane Biogas, biogas polishing technology like Sysadvance,

renewable natural gas distribution with the City of Plano or a private sector gas company,

and subcontractors for operations and project management like JRMA who specialize in

waste management and waste to energy processing.

Future Scope

Possible locations of sorting, pre-treatment, and digester are corporation’s available

space, a transfer station, or a separate facility near the landfill.

Ideally, to reduce processing and labor costs at the site, the digester plant could be

located near an existing MRF (Material Recovery Facility) or landfill. Additionally, this

could reduce the cost of transportation and maintenance while also eliminating the

requirement for a permit to transport the waste. The plant will also need a food processing

system (shredder or separator) in a 50 sq. ft. building. The overall footprint would also

include the gas treatment system and hydrogen SMR reformer.

Due to the restrictions of COVID-19 guidelines, this report will benefit from further analysis

in the following areas.

Waste generation audit/quantity of waste generated by all the corporations from

Plano area

● The characteristics study of food waste generated in a cafeteria

● Engineering design of an anaerobic digester, mass, and energy balance

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● Process flow diagram and facility layout of a proposed facility, requiring work with

an architect

● Detailed cost estimation, including construction, commissioning, installation,

fabrication, and O&M based on facility configurations

● Required funding, investment structures, VPPA/PPA

● Costs/revenues of operating an anaerobic digester, demand-side target audience

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Appendix A

DESIGN PARAMETERS

APPROX. VALUES

Solids Retention Time (SRT)

Hydraulic retention Time

Temperature

pH

Alkalinity

COD Loading Rate

VSS

40 to 120 days

5 to 12 hours

Mesophilic 55°C (Favorable)

7.0 - 7.1 Optimum

2000 to 8000 mg/lit as CaCO3

1 to 50 kg COD/m 3 .day

22-24% of raw waste

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Useful Websites:

https://www.ntmwd.com/, https://www.ntmwd.com/facilities/

www.ucsusa.org/TrashtoTreasure

https://www.epa.gov/sites/production/files/2020-07/documents/20-02-qa_0.pdf

https://www.epa.gov/agstar

https://archive.epa.gov/region9/organics/web/html/index-2.html

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