Treatment Strategies for DBP Reduction. Module 10

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1 Treatment Strategies for DBP Reduction Module 10

2 DBP Control Options Optimize existing facilities Treatment plant Distribution system Make the most of what you ve got! Implement new facilities Treatment plant Distribution system Remote DBP control Evaluate using lifecycle costs!

3 DBP Control Options Treatment Plant Enhanced Coagulation GAC Adsorption PAC Adsorption MIEX Process Alternative Oxidants Bio-treatment Chloramination Distribution System Reduce water age Blending with lower TOC/DBP water Remote DBP control GAC/BAC Aeration

4 Overview of Treatment Technologies Severity of Problem Treatment Capital Cost Mild Alternative Pre-oxidant $ $ Mild Bio-treatment $-$$ $ Moderate Enhanced Coagulation $ $ O&M Cost Moderate PAC $ $$ High Alt. Primary Disinfectant $$-$$$ $-$$$ High MIEX $$-$$$ $-$$$ High GAC $$-$$$ $-$$$ Extreme Chloramines $ $ Extreme Multiple Barrier $$$ $$$

5 Alternative Pre-oxidants Oxidant Dose range (mg/l) Contact time (min) Mode of Action Limitations Eliminate Oxidant Permanganate (KMnO 4 ) Chlorine Dioxide (ClO 2 ) Ozone (O 3 ) Doesn t form DBPs Doesn t form DBPs < No TTHM and HAA5 formation May reduce DS formation No TTHM and HAA5 formation Reduces TOC after biofiltration No Fe & Mn control No biogrowth control Colored water No biogrowth control Chlorite formation Bromate formation Requires biofiltration

6 Alternative Primary Disinfectants Disinfectant Dose range (mg/l) Contact time (min) Mode of Action Limitations Chlorine Dioxide (ClO 2 ) Ozone (O 3 ) Ultraviolet Radiation (UV) < No TTHM and HAA5 formation Reduces d/s formation No TTHM and HAA5 formation Reduces TOC after biofiltration ~ 40 < 20 s Doesn t form mj/cm 2 DBPs Chlorite formation Bromate formation Requires biofiltration Doesn t consume chlorine demand Relatively ineffective for viruses

7 Chloramination Disinfectant Chloramines Dose range (mg/l) Mode of Action Slows TTHM and HAA5 formation Persistent residual Limitations Nitrification in distribution system Requires tight dose control

8 Enhanced Coagulation Dose (mg/l) Contact Time (min) TOC Removal (%) Limitations Coagulant Residuals production Coagulant + Membranes 5-30 < Adding more coagulant lowers ph 1. More TOC is coagulated due to dose and ph 2. Allows lowering of disinfectant dose

9 Coagulation Dose, Contact Time and ph Conditions TOC Reduction with ACH & Ferric Sulfate 5 Filtered Water TOC Concentration (mg/l) Avg. Raw Water TOC Concentration 3.5 mg/l 0 Ferric 15 mg/l 2.5m Ferric 30 mg/l 2.5m Ferric 60 mg/l 2.5m Ferric 15 mg/l 10m Ferric 30 mg/l 10m Ferric 60 mg/l 10m ACH 10 mg/l 2.5m ACH 20 mg/l 2.5m ACH 40 mg/l 2.5m ACH 10 mg/l 10m ACH 20 mg/l 10m ACH 40 mg/l 10m Coagulant Type & Dose ph 6.0 ph 7.0 Ambient ph

10 Powdered Activated Carbon (PAC) Intake PAC PAC PAC PAC PAC B/W PAC removal PAC removal dist. Application Point Intake PAC Contactor Rapid Mix Flocculation Sedimentation Contact Time (min) varies < Mixing poor excellent very good moderate none

11 Granular Activated Carbon (GAC): Filter Adsorber (FA) Conventional treatment with filter media replaced with GAC coagulant disinfectant distribution rapid mix flocculation settling GAC filteradsorber disinfection & storage

12 Granular Activated Carbon (GAC): Post Filter Adsorber (PFA) Conventional treatment with additional GAC filter coagulant disinfectant rapid mix flocculation settling rapid media filtration GAC filtration disinfection & storage Dist. Application EBCT (min) TOC Removal (%) Media Life Media size Limitations Post-Filter Adsorber months 12x40 ES= 0.65 mm Cost/space/hydraulic head Oxidant compatibility

13 Granular Activated Carbon (GAC): TOC Breakthrough Curves % biodegradable DOC C/C % non-adsorbable Operation time, t

14 Magnetic Ion Exchange (MIEX) Filtration

15 MIEX Contact Time (min) TOC Removal (%) Limitations MIEX Cost Footprint Hydraulic head Brine disposal

16 Bio-Treatment Bio-treatment Riverbank Filtration Engineered Biological Filtration Contact Time Acclimation Period TOC Removal (%) Limitations > 30 days none Land Availability Soil conditions 5 10 min > 2 months Temperature Substrate availability No preoxidation

17 Activity Using an example from the systems sketched earlier Identify process changes that you want to investigate and provide three reasons why it might be best

18 Distribution System DBP Control Menu Shorten water age by controlling tank levels, periodic flushing at endpoints, system optimization using existing valving Optimize chlorination strategy throughout the DS by monitoring (replace old pipes, illegal xconn, boost or no boost?) Precursor removal (pre-dbp formation) Optimize existing treatment Install new treatment DBP removal (post-formation) GAC Aeration (TTHM only)

19 Know Your System Determine water age throughout distribution system, particularly at compliance locations Measure chlorine residual throughout distribution system, particularly at maximum distribution locations Quantify TOC removal through treatment processes

20 Getting Started Reduce water age DBPs (µg/l) TTHM Cl 2 residual Chlorine Residual 20 0 Minimum Cl 2 residual Time (days)

21 Getting Started Reduce chlorine residual DBPs (µg/l) TTHM Cl 2 residual Chlorine Residual 20 0 Minimum Cl 2 residual Time (days)

22 Chlorination Strategies Prechlorination Primary Chlorination Booster Chlorination Raw water intake rapid mix flocculation sedimentation filtration disinfection & storage distribution Prechlorination Primary Chlorination Booster Chlorination Oxidation of Fe & Mn Biogrowth control Increased Long CT CT DBPs After Less TOC DBPs removal after TOC removal Pre-filter: longer filter runs Pre-filter: longer filter runs Post-filter: bioremoval of Post-filter: TOC less Cl2 costs Maintains residual for microbial control but could produce more DBPs

23 Chloramination DBPs (µg/l) TOC = 2.5 mg/l Br - = 50 µg/l Cl 2 = 1.25 x TOC ph = 8.0 Temp = 15 C SUVA = 2.0 L/mg/min NH 3 HAA5 TTHM TTHM MCL HAA5 MCL Time (hours)

24 Remote DBP Control Works in isolated areas of high DBPs TTHM aeration (HAA5 not removed effectively by aeration and degrades biologically over time anyway) GAC or BAC (biologically enhanced GAC with O 3 ) WTP Low DBP High DBP Implement Remote DBP Control

25 Remote DBP Control in Distribution Systems Water Treatment Plant Reservoir Stage 2 DBPR Site 80 μg/l TTHM Time

26 TTHM Aeration Strategies THMs can be removed by air stripping Efficiency depends on air and liquid phase transfer (e.g. Henry s Constant for bubble aeration) TTHM reformation after re-chlorination should be evaluated Aeration does not remove HAAs THM Species Henry s Constant (m 3 atmmol -1, 20 C) Chloroform (3.0 ± 0.1) x 10-3 Bromodichloromethane (1.6 ± 0.2) x 10-3 Chlorodibromomethane (8.7 ± 0.2) x 10-4 Bromoform (4.3 ± 0.3) x 10-4

27 TTHM Aeration Strategies In-Reservoir Aeration Strategies Spray Surface External Aeration Strategies Tray / Packed Tower Liqui-Cel Membrane Contactor

28 Photos from a Full-Scale Installation 7.5-hp aerator installed within a 2 MG reservoir

29 Full-Scale Data Following Implementation 100 of Aeration Equipment Concentration (µg/l) Before start of aeration After start of aeration TTHMs Distribution System Sample Site 0750 HAAs Distribution System Sample Site 0750 Jun-1 Jun-6 Jun-11 Jun-16 Jun-21 Jun-26 Jul-1 Jul-6 After start of aeration 23% avg. TTHM reduction achieved Model estimate of 29% reduction at 1.3 MGD

30 Question What can you do if you have remote HAA5 problems?

GAC/BAC Good removal of TTHM up to 10,000 Bed Volumes (BV) for EBCT of 10 min Higher BV for longer EBCT HAA5 removal by both adsorption & biological activities Completely eliminate Cl 2 residual %

31 GAC/BAC Good removal of TTHM up to 10,000 Bed Volumes (BV) for EBCT of 10 min Higher BV for longer EBCT HAA5 removal by both adsorption & biological activities Completely eliminate Cl 2 residual % Removal TTHM 100 B. Johnson (2007) Min EBCT 20 Min 30 Min 20-30% TTHM removal after 30,000 bed volumes and 10 minutes EBCT GAC adsorption effective for ~10,000 bed volumes Bed Volumes HAA5 (µg/l) Inflow Adsorption breakthrough/ Developing biological activity Fully developed GAC Column 4 (10 min EBCT) Initial adsorption biological activity Bed Volumes

Potential Benefits Proven technology Passive treatment Minimal O&M Potential Challenges GAC disposal or reactivation GAC/BAC TOC will govern carbon life expectancy Pilot column tests should be

32 Potential Benefits Proven technology Passive treatment Minimal O&M Potential Challenges GAC disposal or reactivation GAC/BAC TOC will govern carbon life expectancy Pilot column tests should be conducted to better understand a selected manufacturer s GAC performance Reformation of DBPs possible if need to rechlorinate downstream to meet SWTR residual and HPC requirements Customer complaints due to release of GAC fines into DS

33 GAC/BAC Rechlorination Reformation of DBPs Rate of reformation a function of DBP precursor concentration

34 GAC/BAC Considerations Need disinfectant residual to eliminate HPC potentially induced by BAC Release of GAC fines New monitoring locations may be required for Stage 2 DBPR Design and construction based on requirement for treated water

35 Discussion Does your system have a location where remote DBP treatment may be warranted?

36 If your brain looks like this right nowt

37 Then we re pau!

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