Lake Gaston Water Treatment Plant Coagulant Change to
Aluminum Chlorohydrate (ACH)
AWWA Senior Operators Forum
Alex Echols, Chesapeake Public Utilities
Doug Noffsinger, P.E., CH2M HILL
October 9, 2014
Copyright 2013 by CH2M HILL, Inc. • Company Confidential
What are we talking about?
We will present our approach to troubleshooting a submergedtype membrane process durability problem
 Review the overall water system
 Review the plant process flow stream
 Discuss the key role that coagulant addition plays in the
process
 Discuss the approach to improve membrane durability
– Reduce effects of abrasion and membrane strand motion
– Identify and implement an alternative coagulant to allow less mixing
energy (reduced membrane strand movement)


Discuss the approach to identifying an alternative coagulant
Discuss the full-scale implementation of the selected alternative
coagulant and results to date
Copyright 2013 by CH2M HILL, Inc. • Company Confidential
City of Chesapeake Water System Background
Water System Background
City of Chesapeake Department of Utilities Description
 Southeastern, Virginia City of 233,000 population
 Water System Summary
– 63,136 customers treating about 18 MGD
– 2 WTPs
• Northwest River WTP – 10 MGD capacity treating both Northwest River
surface water and brackish groundwater. Uses conventional process
followed by reverse osmosis (RO) membranes and groundwater treatment
with RO membranes as well
• Lake Gaston WTP - 8 MGD capacity treating Norfolk Western reservoir
water supplemented by aquifer storage and recovery (ASR). Uses unique
submerged membrane process.
– 832 miles of distribution pipe
– Purchase water from Norfolk and Portsmouth as well
Copyright 2013 by CH2M HILL, Inc. • Company Confidential
Copyright 2013 by CH2M HILL, Inc. • Company Confidential
Water Service Systems
Copyright 2013 by CH2M HILL, Inc. • Company Confidential
Lake Gaston Water Treatment Plant
Lake Gaston Water Treatment Plant


City Council OK’s moving forward – November 2000
Five components of the project:
–
–
–
–
Water Treatment Plant
Pipeline on Military Highway
Pipeline on Jolliff Road
Intake Structure on
In-town Lakes
– Tank and Pump
Station on Jolliff
Road
Copyright 2013 by CH2M HILL, Inc. • Company Confidential
Lake Gaston Water Treatment Plant
Process Flow Stream
Copyright 2013 by CH2M HILL, Inc. • Company Confidential
Lake Gaston Water Treatment Plant
Process Flow Stream
Rapid
Raw
Water
Mix
Flocculation Permeate
Pump
Manganese
Contactor/
Disinfection
Treated
Water
Coagulant
Reject
Air
10
Copyright 2013 by CH2M HILL, Inc. • Company Confidential
Lake Gaston Water Treatment Plant

Capacity:
– 8 mgd for 4 trains (2 mgd/train); 7.6 mgd at 95% recovery
– 6 mgd for 3 trains (2 mgd/train); 5.7 mgd at 95% recovery

Unit Processes
– Rapid Mix:
• Raw Water Strainer
• In-Line Rapid Mix
– Flocculation Basins
• Two Stage Basin
• Flocculation Mixer
– Membrane Basins
• Number of active Basins: 4
• Membranes: Immersed hollow-fiber ultrafiltration
Copyright 2013 by CH2M HILL, Inc. • Company Confidential
Lake Gaston Water Treatment Plant

Unit Processes (Continued)
–
–
–
–
–
–
Manganese Contact Filters (adsorbers)
Disinfection Pipeline
Gravity Thickener
Centrifuge Dewatering
2 MG Finished Water Storage Tank
Chemical Feed
•
•
•
•
•
•
Ferric Chloride - coagulant
Polymer – coagulant aid (for thickening and dewatering)
Sodium Hydroxide – pH and alkalinity control
Citric Acid – membrane cleaning agent
Sodium Hypochlorite – Primary disinfectant
Ammonia – Secondary (residual) disinfectant additive (formation of
combined chlorine by reaction with free chlorine)
Copyright 2013 by CH2M HILL, Inc. • Company Confidential
Submerged Membrane Ultrafiltration (UF) Process
Operation
Production Flow
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Backpulse Flow
Ultrafiltration Operation
Air Line
Permeate
Header
500d
Cassettes
Reject
Production Flow
Copyright 2013 by CH2M HILL, Inc. • Company Confidential
Coagulant Addition at the Lake Gaston WTP

Coagulant addition plays a key role in water treatment at Lake
Gaston WTP
– The only part of the process that removes dissolved organic material
which is the key to minimizing disinfection by-product (DBP) formation
– Works at relatively low pH (high 5’s and low 6’s) to achieve maximum
organic removal without producing significant dissolved iron
– Acidic nature helps depress pH to meet low pH coagulation goal

Initial coagulant selection was Ferric Chloride (FECL3) based on
pilot scale testing
– FECL3 achieved DBP goals
– Confirmed that clarification process could be omitted
– Did not exhibit negative material effects on membranes during testing
Copyright 2013 by CH2M HILL, Inc. • Company Confidential
Approach to Improve Membrane Durability
Membrane Durability Problems

Since the start of operations in 2005, membrane durability has not
met expectations (5-10 year service life)
– Membranes are designed to achieve primary disinfection of protozoa
and most bacteria through particle removal
– High rate of membrane failure reduced the required removal
performance measured as a Log Removal Value (LRV) of 3.
– Membranes needed replacement on a 2-3 year basis to avoid noncompliance with LRV requirements.

Evaluation Results
– Abrasion and/or material fatigue appears to be the cause of reduced
membrane durability
– The abrasion effects may be reduced with lower applied mixing energy
– A change to an alternative coagulant may be beneficial in support of
reduced mixing energy operation
Copyright 2013 by CH2M HILL, Inc. • Company Confidential
Identification of an Alternative Coagulant
Coagulant Selection Goals:

Water Quality Compliance
–
–
–
–

Keep THM/HAAs at or below existing levels
Keep lead & copper below the Action Level
Keep NPDES discharge non-toxic
Keep residuals (sludge) aluminum leachate at
acceptable levels.
Process
– Reduced floc size for better performance in
membrane basin (reduced mixing energy)
– Gravity thicken well and produce a low-solids
overflow (decant)
– Produce less solids
– Operate at a higher pH
Copyright 2013 by CH2M HILL, Inc. • Company Confidential
Alternative Coagulant Testing Approach
Testing Objective


Evaluate candidate coagulants for DOC reduction performance
Full-scale testing of the coagulant that may achieve both DBP
compliance and an increase in membrane life.
Evaluation Program Framework
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Step 1 – Desk-top coagulant screening
Step 2 – Jar-test potential coagulants to determine DOC reduction
Step 3 – Confirm DBP control performance of the selected
coagulant identified in Step 2 using a laboratory simulation of the
plant and distribution system
Step 4 – Full(plant)-scale implementation of the selected
coagulant to confirm the above and determine adjustments
needed for long-term operation
Copyright 2013 by CH2M HILL, Inc. • Company Confidential
Step 1 – Alternative Coagulant Screening Approach
Criterion
A benchmark coagulant must be selected
for comparison of alternatives
Discussion
Ferric chloride (FeCl3) is currently used and was
selected as the benchmark comparison coagulant.
An alternative coagulant must be selected
that:
•
Is approved for potable use.
•
Meets or exceeds current DBP
formation potential performance.
Coagulants with relatively high unit-cationic charge
density are considered to be the best candidates for
DBP control.
•
Does not coat or foul the submerged
membranes.
The more likely coagulant candidates to meet the
criteria were thought to be aluminum-based.
•
Produces a “pin” floc.
•
Therefore, products that contain aluminum oxide
contents equivalent to the typical aluminum sulfate
Does not produce undesirable byproducts, such as high soluble metals or solution (alum) were tested.
negative impacts on residuals
Alum was also tested as a benchmark for comparison.
operations.
Copyright 2013 by CH2M HILL, Inc. • Company Confidential
Step 2 – Coagulant Jar Testing

Four alternative coagulants were identified as good candidates for
consideration based on dissolved UV 254 adsorbance and
dissolved organic carbon (DOC) removal:
– 2 poly-aluminum chloride (PACL) products
– Aluminum chloride
– Aluminum chlorohydrate (ACH)
Copyright 2013 by CH2M HILL, Inc. • Company Confidential
Step 3 – Lab Simulated Distribution System Testing

Simulated Distribution System lab scale testing for DBP levels
– Simulated free chlorine contact time
– Quenched free chlorine residual using ammonia at a dosage that
simulated plant effluent residual chloramine levels.
– Held the chloraminated sample for a time period equivalent to the
Locational Running Annual Average (LRAA) “High TTHM” sampling
site travel time period (approximately 23 hours)
– Simulated sample site pH as well
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Step 3 – Simulated Distribution System DBP Testing
Results
THM Formation
80
Jar Test 1 - Ferric Chloride
Jar Test 2 - DelPAC XG (ACH)
70
Jar Test 3 - Aluminum Chloride
Jar Test 4 - DelPAC 1525
60
Total THM (ug/L)
Jar Test 5 - DelPAC 2950
50
40
30
20
10
0
0
12
24
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36
48
60
72
Time (hrs)
84
96
108
120
Step 3 – Simulated Distribution System DBP Testing
Results

A few interesting things to note from lab THM testing:
– All coagulants produced DBP results in compliance with the LRAA DBP
limits of 80 μg/L for THMs and 60 μg/L HAA5 respectively.
– While there is some relative variation in the observed DBP levels for each
alternative coagulant treatment regimen, the differences are very minor
and can be understood to be effectively equivalent in performance.
– The data confirm that even though ammonia is added to “quench” the
effect of free chlorine on DBP formation, formation of DBPs continue to
some extent.
– The laboratory-scale SDS testing data is consistent with observed fullscale, real-time results experienced during water delivery operations.
Copyright 2013 by CH2M HILL, Inc. • Company Confidential
Step 3 – Lab Testing Summary Information
Coagulant
Test
Dosage
Test Dosage
SDS LRAA
THM Level
Approx.
Chemical
Unit Cost
Unit Sludge
Production
Factor
Estimated
Unit Sludge
Production
mg/L
μg/L
$/lb.
$/MG
mg/mg
lbs./MG
Ferric Chloride
(FECL3)
17
23.64
$0.23
$33
0.66
94
Aluminum
Chloride
65
22.52
$0.35
$190
0.21
115
Aluminum
Chlorohydrate
(DelPAC XG) (ACH)
38
22.20
$0.25
$79
0.36
114
Polyaluminum
Chloride
(DelPAC 2950)
62
21.26
$0.23
$119
0.27
141
Polyaluminum
Chloride
(DelPAC 1525)
64
18.44
$0.16
$85
0.17
88
Coagulant
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Est.
Cost/
MG
Step 3 – Lab Testing Summary Information

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The data indicates that a change in coagulant can achieve the same DBP
control performance as the current coagulant.
A change to one of the alternative coagulants will double the unit
treatment cost for coagulant addition. However, the coagulant may not
require as much (or any) addition of sodium hydroxide for pH control.
The lowest cost alternative coagulants were aluminum chlorohydrate
(ACH) and a poly-aluminum product (PACL).
The relative dosages and calculated sludge production impacts are
essentially equivalent due to the complexity and nature of the reactions
involved and the methods used for residuals production estimation.
The use of ACH is common at similar membrane installations. The DBP,
cost performance, and sludge production results indicate no barrier for
potential use at the LGWTP.
Therefore, ACH was recommended for full-scale testing
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Step 4 – Full-Scale Coagulant Testing

Full Scale test
– Why: To evaluate coagulant under actual Plant and distribution system
conditions and determine:
• UV254, TOC removal, and distribution system DBP control.
• Operational effects/impacts such as membrane LRV, fiber effects, TMP, and
fouling
• Solids production, impact on thickener, impact on DEQ discharge permit,
etc.
• Process adjustments such as chemical dosages, pH levels, etc.
– How:
•
•
•
•
Duration: 12 months
Develop plant operational scheme to accommodate the use of ACH
Obtain VDH approval
Obtain DEQ NPDES and VPA approval
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ACH Full Scale Implementation
Key Implementation Actions


Prepared Summary Reports for Regulatory
Approval
Virginia Department of Health – Drinking
Water Quality
– Alternative Coagulant and Test Plan Approval
– Requirement to perform full-scale lead and
copper compliance monitoring

Department of Environmental Quality –
Surface Water Discharge and Residuals
Disposal Monitoring
– Acute and chronic toxicity testing of thickener
overflow (decant) and NPDES permit
compliance confirmation
– Residuals dewatered cake testing for aluminum
and other metals
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Key Implementation Actions

Plant facilities preparation
– Chemical systems prep –
storage tanks and feed pumps
– Process tankage draining and
purging of FECL3 floc
– Turn-down of mixing blowers
and durations
Copyright 2013 by CH2M HILL, Inc. • Company Confidential
ACH Conversion


ACH conversion occurred on June 15, 2014
Operational Actions:
– Current polymer works well with thickener and centrifuge
– Maintaining thickener Depth of Blanket (DOB) between 5 to 10 feet – looking good
– Perform normal routine membrane operation:
•
•
•
•

Perform routine Pressure Integrity (PIT) Tests – looking good
Perform routine Clean In Place (CIP) actions – looking good
Log Reduction Value (LRV) calculations – looking good
Few fiber repairs needed to date
Monitoring Actions:
– Inspecting solids accumulation in fibers
– Monitor thickener performance
– VDH: Performing Lead and Copper testing in accordance with VDH test approval
conditions
– VPDES: Performing testing of Gravity Thickener Overflow for chronic toxicity and
aluminum
– VPA: Perform additional aluminum testing of LGWTP residuals, NWRWTP
residuals, and combined residuals
Copyright 2013 by CH2M HILL, Inc. • Company Confidential
Results to Date

Much improved LRV performance
– High initial LRVs
– LRV values are maintained – very little reduction

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DBP levels are equal to or less than FECL3
Has drastically reduced membrane strand repairs
Lower energy operation does not produce any process or
maintenance issues
Thickener performance drastically improved (unexpected!)
Dewatering performance appears to be equal to or better than
FECL3
All other regulatory testing to date appears to indicate compliance
requirements are being met
City is considering using ACH at the NWR WTP
Copyright 2013 by CH2M HILL, Inc. • Company Confidential
Discussion