Systematic Approach to Water Treatment Plant ... - Ohiowater.org

SYSTEMATIC APPROACH TO WATER TREATMENT PLANT PROCESS
OPTIMIZATION AND WHY SHOULD SURFACE WATER TREATMENT
PLANTS MONITOR UV254 IN SOURCE WATER
Alex Yavich, Ph.D., P.E.
Optimization Solutions Environmental, LLC

What Will Be Discussed
‣ Chemical feed rate optimization
‣ Coagulant choice
‣ Rapid and flocculation mixing
‣ UV254 monitoring

Chemical Feed Rate Optimization
‣ Ensuring adequate chemical feed rates under all plant
conditions is the first step in water plant process optimization
‣ Optimization of chemical feed rates not only improves
effluent quality and reduce chemical usage, but also helps
identify other potential areas for improvement

Coagulation Feed Optimization
Optimization
goal
Computer models can be developed to provide real time advisement to the
operators of the optimal chemical feed rates under various plant conditions

Case 1
Three Rivers Filtration Plant, Fort Wayne, IN
• Total capacity: 72 MGD
• Source water: St. Joseph River

Case 1: Raw Water Quality

Case 1: Treatment train
Fe 2 (SO 4 ) 3
Lime
PAC
Fe 2 (SO 4 ) 3
CO 2
Influent
Primary Coagulation /
Lime Softening Stage
Second Coagulation
Stage
Filtration
Effluent

Chemical Feed Control at Fort Wayne Plant

Case 1: Chemical feed optimization
1
All costs in 2011 chemical prices

Optimal Coagulant
‣ Optimal coagulant is the coagulant that best meets
plant’s operational goals
‣ By choosing the right coagulant, a water treatment
plant can significantly improve its process
performance and the quality of finished water

What are the Choices
‣ Metal salts
Turbidity removal through charge neutralization and sweep coagulation
of colloidal particles
Commonly used coagulants: alum, ferric sulfate, ferric chloride,
polyaluminum chloride
‣ Cationic polymers
Charge neutralization is major coagulation mechanism
Wide range of products available

Optimal Coagulant: Major Considerations
‣ Raw water quality: turbidity, pH, alkalinity, NOM etc.
‣ Operational objectives: effluent quality, chemical cost,
sludge production, filter run etc.
‣ Plant size
‣ Treatment train: lime softening, UV disinfection etc.
‣ Hardware: flocculators (variable/constant speed), clarifiers
(conventional basins, upflow clarifiers, plate settlers etc.), filter
configuration (media type, size, support etc.)

Case 2
Holland Water Treatment Plant
Holland, MI
Capacity:
Source water:
38.5 MGD
Lake Michigan

Case 2: Raw Water Quality
Raw Water Parameters
Typical Range
Temperature, o F
32 – 77
Alkalinity, mg/L as CaCO 3
100 – 145
Turbidity, NTU
0.3 – 40
Total organic carbon, mg/L
1.6 – 2.5
UV254, cm -1 0.01 – 0.2

Case 2: Holland WTP Schematic
Cl
Coagulant
Raw
water
Low lift pump
MIxing
Chamber
Flocculation
Basins
Settling basins
Filters
Cl
Treated
water
Clearwell
High lift
pumps

Operational Goal
• Alum was historically employed for coagulation
• Sludge production was problematic
• Goal – reduce sludge production

Alternative Coagulants Tested
• PACl
• Alumer (a premanufactured blend of alum and cationic
polymer)
• “Seasonal” coagulation practice
– Alum: December thru April
– Alumer: May thru November

Coagulation Computer Models at HWTP

Results of Full-Scale Testing and
Computer Simulation Analysis
• PACl
– Sludge could be reduced by up to 45 percent
– Cost would increase by appr. 20%
– Potential turbidity problems on four Integral Media Support (IMS)
cap filters
• Alumer
– Sludge could be reduced by up to 35 percent
– Cost would increase by 5-15%
– Not cost effective at increased UV254
• “Seasonal” coagulation practice
– Sludge could be reduced by up to 25 percent
– No cost increase (compared to alum)
– More complex operation

Plant’s Best Choice (current practice)
Alum and Cationic Polymer (fed separately)
• Sludge reduced by up to 35 percent
• Expected cost reduction by 25 - 30 percent (compared to alumer)
• Consistent filtered turbidity
• Improved operational control
• Can be optimized to meet plant’s future goals

What Affected the Choice of Coagulant at HWTP
• Raw water quality: turbidity and NOM
• Operational goals: sludge production, effluent quality, chemical costs
• Treatment train: sedimentation basins, filter configuration, feeding
equipment

Rapid and Flocculation Mixing
Raw
water
Low lift
pump
Coagulant
Mixing
Chamber
Flocculation
Basin
Settling basin
Mixing Intensity (G-value)
G = (P/μV) 1/2
G – velocity gradient, s -1
P – power input, ft·lb/s
µ – dynamic viscosity, ft·s/ft 2
V – volume, ft 3

Rapid and Flocculation Mixing
Raw
water
Low lift
pump
Coagulant
Mixing
Chamber
Flocculation
Basin
Settling basin
Operation Mixing Time G value, s -1
Rapid mixing 1 – 60 sec 600 - 1500
Flocculation 20 – 30 min 40 - 70

Case 3
St. Joseph Water Filtration Plant
St. Joseph, MI
Capacity:
Source water:
Raw turbidity:
Treatment:
12 MGD
Lake Michigan
1 – 60 NTU
Alum coagulation
No rapid mixer

Case 3: Plant Schematic
Cl
NaOH
Alum
Raw
water
Low lift pump
Sludge
Drain
Accelator Clarifiers (3)
Filters
Cl
Treated
water
Clearwell
High lift
pumps

Case 3: Rapid Mixing Analysis
Type MIxing time, s G value, s -1
St. Joseph plant
(hydraulic mixing in the pipe)
10 - 60 100 - 400
Mechanical mixers
(for comparison) 10 - 60 600 - 1000
In-line blenders
(for comparison) 0.5 - 1 1000 - 1500

Case 3: Computer simulation analysis

Case 3: Effect of coagulant mixing

Case 4
Holland Water Treatment Plant
Holland, MI
Capacity:
Source water:
38.5 MGD
Lake Michigan

Case 4: Effect of Flocculation Mixing on Filtered
Turbidity

Water Quality Monitoring: UV254
‣ UV254 is a measure of ultraviolet absorption at a wavelength
of 254 nm
‣ UV254 is a surrogate measure of natural organic matter
(NOM) in water

Why Should Surface Water Treatment Plants
Monitor UV254 in Raw Water
Coagulation
Filtration
Clarification
UV254
DBP control
Taste and Odor
Control
Disinfection

Case 5: Effect of UV254 on coagulant demand
Lake Michigan Filtration Plant, Grand Rapids, MI
Capacity – 130 MGD
Source – Lake Michigan

Case 6: Effect of UV254 on effluent turbidity
South Haven Water Treatment Plant, South Haven, MI
Capacity – 4 MGD
Source – Lake Michigan

UV254 Analysis is Fast and Simple

Benefits of UV254 Monitoring
‣ Improved chemical feed control
‣ Consistent effluent turbidity
‣ Reduced chemical costs
‣ Important factor in identifying the “optimal”
coagulant
‣ Improved DBP control
‣ Helps optimize UV disinfection

Summary
Ensure that chemical feed rates are satisfactory under all
plant conditions
Does the plant use the right coagulant
Verify that rapid mixing operation is adequate
Adjust, if possible, flocculation speed at least seasonally
Implement raw water UV254 monitoring (surface WTPs)

Q&A
Alex Yavich
Ph. (616) 975-0847
E-mail: yavichal@osenv.com
Web: www.osenv.com