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Disinfectant & Disinfection Byproducts Control and Optimization. Case Study of the University of Alaska Fairbanks Water System. By Johnny Mendez, P.E., Drinking Water Program Alaska Department of Environmental Conservation. Prepared in Cooperation with Ben Stacy, WTP Supervisor,

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Disinfectant disinfection byproducts control and optimization l.jpg

Disinfectant & Disinfection Byproducts Control and Optimization

Case Study of the University of Alaska Fairbanks Water System

By Johnny Mendez, P.E.,

Drinking Water Program

Alaska Department of Environmental Conservation

Prepared in Cooperation with Ben Stacy, WTP Supervisor,

University of Alaska Fairbanks.

Note: The D/DBP optimization and control concepts being presented here have been adapted from a ADEC training workshop in Fairbanks, AK Feb 26-Mar 1, 2007. The workshop was developed by Mr. Larry DeMers, PE of Process Applications Inc.

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Disinfectant vs. DBP balance Optimization

  • Optimized disinfection at WTP and Distribution System improves barrier against microbial pathogens


  • (Cl or O3)+ Organics  DBPs (TTHM, HAA5, Bromate)

  • The challenge is to balance these competing goals

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DBP Health effects Optimization

  • Suspected Carcinogens

  • Suspected to affect reproduction

  • Large population exposure to DBPs

  • Other potential DBPs health effects have not been fully researched

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Optimization goals for Disinfection & DBP Control Optimization

  • Methodology developed from CPE concepts used at media filtration WTPs.

    • Optimization goals

    • Use of special studies (scientific method)

  • Process Applications Inc. and EPA effort.

  • Basis for Optimization Goals:

    • Public health protection

    • Safety factor for achieving compliance

    • Provide means to measure improvements

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D/DBP Optimization Goals Optimization

  • TOC Performance Goals:

    • (% TOC removed/% removal required)=1.1 (10% safety factor)

    • Finished water TOC concentration= goal WTP specific

  • Disinfection Goals:

    • Maintain sufficient inactivation CT (safety factor is system specific)

    • Maintain minimum distribution system residual:

      • Free Chlorine ≥ 0.2 mg/l

      • Total Chlorine = system specific (suggest >0.5 mg/L)

  • DPB Goals:

    • Individual site LRAA: TTHM≤ 80 ppb; HAA5 ≤ 60 ppb

    • Long Term System Goal (based on 11 quarter average of Max LRAAs): TTHM≤ 60 ppb; HAA5 ≤ 40 ppb

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D/DBP Optimization Tools Optimization

  • Historical Cl2 and CT Spreadsheet

    • WTP Cl dose, Cl residual, and CT assessment

  • Historical Chlorine Residual Performance Spreadsheet

    • assess historical Cl residual trends for WTP effluent and distribution system

  • Historical TOC performance Spreadsheet

    • assess WTP TOC removal performance

  • Historical DBP Performance

    • Assessment of historical DBP performance vs. new optimization goals

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Develop a WQ Baseline and Monitoring Plan Optimization

  • Before changes in the water system are implemented a water quality baseline is needed to:

    • Understand historical system performance in light of optimization goals

    • Help fine tune/set optimization goals

    • Have a basis of comparison for measuring improvements in DPB control

    • Anticipate and prepare for potential secondary impacts

  • A monitoring plan will help in the systematic and efficient collection of data for the baseline.

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Developing a Baseline Optimization

  • Select which relevant WQ parameters to monitor (i.e. TOC, Alkalinity, CT, TTHM).

  • Some parameters may already be available, but frequency may need to be modified.

  • Consider use of surrogate parameters for ease of data collection & cost savings (e.g. TOC and DBP surrogates)

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Surrogates for DBP related data Optimization

  • Developing a DBP control strategy may require increased TOC and DBP data. This can increase cost and complexity of data collection

  • Tools exist to enhance TOC and DBP data quantity by using alternative field methods that are faster and less costly

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Field TOC Methods Optimization

  • UV absorbance at 254 nm:

    • Uses spectrophotometer

    • Samples need to be filtered

    • Requires development of relationship b/w UV254 and TOC

    • Best for water samples before Cl addition

  • Field TOC method (HACH®):

    • Uses reagents and spectrophotometer

    • Issues with accuracy & precision

  • Portable TOC analyzer (GE):

    • costly equipment (~ $15K)

    • Easy to use and calibrate

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TOC and UV Optimization254 Relationship






TOC (mg/L)










UV Absorbance at 254 nm (1/cm)

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Field DBP Methods Optimization

  • Cl residual Decay

    • Simple, can be done by all WTP operators

    • Cl residual is used as surrogate for DBP formation

    • Relationship may change through the year due to WQ and temp. changes

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Field DBP Methods (cont.) Optimization

  • THM Plus™ ( HACH®)

    • Uses spectrophotometer and 4 reagents

    • Measures 4 THM species plus other trihalogenated DBPs:

      • Chloroform

      • Bromodichloromethane

      • Dibromochloromethane

      • Bromoform

      • Trichloroacetic acid, plus other HAAs, & Chloral Hydrate.

    • Results can be obtained in 1-2 hrs.

    • Paired sampling needed to develop relationship b/w field and analytical values.

    • Cost ~$5 to $10 per sample once equipment purchased

    • Spectrophotometer cost ~$3000 (DR2800) to $6000 (DR5000)

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THM-Plus Method Optimization

  • HACH® Method 10132

  • The method can be run on any Hach DR 5000, DR 2800, DR 4000, DR 3000, DR 2400, DR 2010, or DR 2000 Spectrophotometer

  • Results Measured at 515 nm

  • Results reported as ppb chloroform

  • Range 0-600 ppb

  • Sensitivity ~10 ppb

  • Precision= 66 ppb (95% confidence range= 53 ppb-79 ppb)

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Creating a Monitoring Plan Optimization

  • Develop objective for the monitoring

  • Answer sampling specifics (what, where, how, who, frequency)

  • Suggested min. monitoring:

    • TOC & DBPs (including surrogates)-> monthly

    • Disinfectant residuals at WTP->Daily

    • Disinfectant Residuals in Distribution->Weekly

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What Next: Optimizationwhat to do With All this Data?

  • Create Graphs to see trends

  • Make list of issues/sites to focus on

  • Develop relationships with surrogate parameters to help in process control

  • Develop DBP control strategies for testing

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Developing a DBP Control Strategy Optimization

  • Operations-based change that will lower DBPs

  • Use “Special Studies” approach

    • Hypothesis, Methods/Resources, Experimental Design, Results/Conclusions, implementation

  • Take small steps

  • Pay attention to secondary impacts

  • Develop implementation strategy

    • Use data to sell idea to management

    • Think of scale (Seasonal/Year-round?, WTP/Distribution?)

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DBP Control Strategies--Examples: Optimization

  • Lowering TOC

  • Optimize Chlorine Use (pre-chlorination, intermediate, & post chlorination)

  • Optimize Process pH

    • Higher pH (>8.5) higher TTHM formation Potential

    • Lower pH (<6.5) higher HAA formation potential

  • Reduce water age

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University of Alaska Fairbanks (UAF) Optimization

Case Study

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UAF Water System Facts Optimization

  • Population: 3600 Non-Transient, 1400 Resident

  • 2600 acre campus (230 acres developed)

  • Design Capacity= 1 MGD; Typically runs < 0.5 MGD (350 gpm)

  • Source: Ground water wells (3 wells)

    • High Iron 15 mg/l

    • High Mn 1.5 mg/l

    • High TOC~13 mg/l

  • Treatment:

    • Objective: Fe & Mn & Organics removal (Benzene)

    • Pre-Oxidation (Permanganate)

    • High Rate Aeration,

    • Coagulation: Nalco 7768 Anionic Polymer & 8185 PAC polymer,

    • Flocculation: 2-Stages, 20 min to 2 hrs detention time

  • -- Arsenic45ppb

    -- pH 7 to 8

    -- Alkalinity~310-350 mg/L

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    UAF Water System Facts (cont.) Optimization

    • Treatment (cont.):

      • Sedimentation: 300 Tube Settlers, (settled water turbidity ~1.0-3.0NTU)

      • multi-media filtration: Anthracite, Sand, Gravel (turbidity ~.05-.07 NTU)

      • GAC (10 filters, run 5 at time)

      • Corrosion inhibitor (zinc sulfate),

      • Storage (1.5 MGal),

      • Chlorination (MIOX Sal-80): Target entry point Cl residual ~1.5 ppm.

    • Distribution:

      • ~ 6-miles of pipe

      • Parallel fire protection and domestic water mains

      • Mainly 8” and 10” diameter DI Pipes

      • Water pipes in utilidor shared by steam lines

      • ~100 service connections

      • Highest Water Temp ~72oF

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    UAF Optimization

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    WTP Optimization

    O’ Neill



    Student Housing
















    University of Alaska Fairbanks

    Distribution System



    Power Plant

    • Notes:

    • Not to Scale,

    • Simplified Diagram; not all service connections or branches shown

    • Water mains are mostly 8-in. diameter. Some sections are 10-in.

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    UAF DBP Study Strategy Optimization

    • Cl data

    • TOC data

    • Develop Cl Map in Distribution

    • Collect CL residual

    • Collect THM Plus data

    • Collect TTHM data and HAA5

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    Historical data Optimization

    • TOC

    • CL

    • DBP

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    Latest Developments Optimization

    • THM-Plus data

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    What Next? Optimization

    • Select Stage 2 sites

    • IDSE

    • Treatment changes:

    • Coagulation enhancement

    • Carbon Filter Special Study?

    • Membrane system?

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    Sources Optimization

    • ADEC D/DBP Training February 26, 2007. Larry DeMers, Process Applications Inc., Ft. Collins, CO.

    • UAF Water Distribution Condition Survey. PDC, Inc. Consulting Engineers; Project 2001110CWS, Final Report. November 2001.

    • ADEC SDWIS Database

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    Questions? Optimization