lake gaston water treatment plant coagulant … operations/lgwtp ach 100914.pdflake gaston water...

Copyright 2013 by CH2M HILL, Inc. • Company Confidential

Lake Gaston Water Treatment Plant Coagulant Change to Aluminum Chlorohydrate (ACH)

AWWA Senior Operators ForumAlex Echols, Chesapeake Public Utilities Doug Noffsinger, P.E., CH2M HILLOctober 9, 2014


What are we talking about?

We will present our approach to troubleshooting a submerged-type 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

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


Water Service Systems

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 JolliffRoad


Lake Gaston Water Treatment Plant Process Flow Stream


Lake Gaston Water Treatment Plant Process Flow Stream

Air

PermeatePump

Reject

Treated Water

FlocculationManganese Contactor/Disinfection

Raw Water

Coagulant

RapidMix

10



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



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)


Production Flow Backpulse Flow

Submerged Membrane Ultrafiltration (UF) ProcessOperation


Production Flow

Air Line

Permeate Header

500d Cassettes

Reject

Ultrafiltration Operation


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

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 non-

compliance 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


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


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 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


Step 1 – Alternative Coagulant Screening ApproachCriterion Discussion

A benchmark coagulant must be selected for comparison of alternatives

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.

• Does not coat or foul the submerged membranes.

• Produces a “pin” floc.

• Does not produce undesirable by-products, such as high soluble metals or negative impacts on residuals operations.

Coagulants with relatively high unit-cationic charge density are considered to be the best candidates for DBP control.

The more likely coagulant candidates to meet the criteria were thought to be aluminum-based.

Therefore, products that contain aluminum oxide contents equivalent to the typical aluminum sulfate solution (alum) were tested.

Alum was also tested as a benchmark for comparison.


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)


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


Step 3 – Simulated Distribution System DBP Testing Results

0

10

20

30

40

50

60

70

80

0 12 24 36 48 60 72 84 96 108 120

Tota

l TH

M (u

g/L)

Time (hrs)

THM Formation

Jar Test 1 - Ferric Chloride

Jar Test 2 - DelPAC XG (ACH)

Jar Test 3 - Aluminum Chloride

Jar Test 4 - DelPAC 1525

Jar Test 5 - DelPAC 2950


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 full-scale, real-time results experienced during water delivery operations.


Step 3 – Lab Testing Summary Information

Coagulant

Coagulant Test Dosage

Test Dosage SDS LRAATHM Level

Approx. Chemical Unit Cost

Est. Cost/ MG

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

PolyaluminumChloride(DelPAC 2950)

62 21.26 $0.23 $119 0.27 141

PolyaluminumChloride(DelPAC 1525)

64 18.44 $0.16 $85 0.17 88


Step 3 – Lab Testing Summary Information

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


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

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


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


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


Results to Date

Much improved LRV performance– High initial LRVs– LRV values are maintained – very little reduction

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

Discussion

lake gaston water treatment plant coagulant … operations/lgwtp ach 100914.pdflake gaston water...

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