SYSTEMATIC APPROACH TO WATER TREATMENT PLANT PROCESS

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
Fe2(SO4)3
Lime
Fe2(SO4)3
PAC
CO2
Primary Coagulation /
Lime Softening Stage
Influent
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:
38.5 MGD
Source water:
Lake Michigan
Case 2: Raw Water Quality
Raw Water Parameters
Temperature, oF
Alkalinity, mg/L as CaCO3
Turbidity, NTU
Total organic carbon, mg/L
UV254, cm-1
Typical Range
32 – 77
100 – 145
0.3 – 40
1.6 – 2.5
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
Coagulant
Raw
water
Low lift
pump
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/ft2
V – volume, ft3
Rapid and Flocculation Mixing
Coagulant
Raw
water
Low lift
pump
Mixing
Chamber Flocculation
Basin
Settling basin
Mixing Time
G value, s-1
Rapid mixing
1 – 60 sec
600 - 1500
Flocculation
20 – 30 min
40 - 70
Operation
Case 3
St. Joseph Water Filtration Plant
St. Joseph, MI
Capacity:
12 MGD
Source water:
Lake Michigan
Raw turbidity:
1 – 60 NTU
Treatment:
Alum coagulation
No rapid mixer
Case 3: Plant Schematic
Cl
NaOH Alum
Raw
water
Sludge
Low lift pump
Drain
Accelator Clarifiers (3)
Filters
Cl
Treated
water
Clearwell
High lift
pumps
Case 3: Rapid Mixing Analysis
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
Type
Case 3: Computer simulation analysis
Case 3: Effect of coagulant mixing
Case 4
Holland Water Treatment Plant
Holland, MI
Capacity:
38.5 MGD
Source water:
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
UV254
Clarification
Taste and Odor
Control
DBP 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: [email protected]
Web: www.osenv.com