DBP Treatment Strategies. Learning Objectives. DBP Control Options Optimize existing facilities

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1 DBP Treatment Strategies Workshop developed by RCAP/AWWA and funded by the USEPA Learning Objectives Describe treatment strategies to address DBP formation Evaluate the various strategies to choose the best one for your system 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! Developed by AWWA in partnership with RCAP and funded by USEPA, Published 215 1

2 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 Overview of Treatment Technologies Severity of Problem Treatment Capital Cost O&M Cost Mild Alternative Pre-oxidant $ $ Mild Bio-treatment $-$$ $ Moderate Enhanced Coagulation $ $ Moderate PAC $ $$ High Alt. Primary Disinfectant $$-$$$ $-$$$ High MIEX $$-$$$ $-$$$ High GAC $$-$$$ $-$$$ Extreme Chloramines $ $ Extreme Multiple Barrier $$$ $$$ Alternative Preoxidants: General Performance Oxidant Eliminate Oxidant Permanganate (KMnO 4 ) Chlorine Dioxide (ClO 2 ) Ozone (O 3 ) Dose range (mg/l) Contact time (min) Mode of Action 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 Limitations No Fe & Mn control No biogrowth control Colored water No biogrowth control Chlorite formation Bromate formation Requires biofiltration Developed by AWWA in partnership with RCAP and funded by USEPA, Published 215 2

3 Alternative Primary Disinfectants: General Performance Disinfectant Chlorine Dioxide (ClO 2 ) Ozone (O 3 ) Ultraviolet Radiation (UV) Dose range (mg/l) Contact time (min) Mode of Action < No TTHM and HAA5 formation Reduces d/s formation No TTHM and HAA5 formation Reduces TOC after biofiltration ~ 4 < 2 s Doesn t form mj/cm 2 DBPs Developed by American Water Works Association with funds from the U.S. Environmental Protection Agency, Published 215 Limitations Chlorite formation Bromate formation Requires biofiltration Doesn t consume chlorine demand Relatively ineffective for viruses Chloramination Disinfectant Dose range (mg/l) Mode of Action Chloramines.5 4 Slows TTHM and HAA5 formation Slow decay Limitations Nitrosamines formation Nitrification in distribution system Requires tight dose control Enhanced Coagulation Dose (mg/l) Contact Time (min) TOC Removal (%) Limitations Coagulant Residuals production Coagulant + Membranes 5-3 < Adding more coagulant lowers ph 1. More TOC is coagulated due to dose and ph 2. Allows lowering of disinfectant dose Developed by AWWA in partnership with RCAP and funded by USEPA, Published 215 3

4 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 Ferric 15 mg/l 2.5m Ferric 3 mg/l 2.5m Ferric 6 mg/l 2.5m Ferric 15 mg/l 1m Ferric 3 mg/l 1m Ferric 6 mg/l 1m ACH 1 mg/l 2.5m ACH 2 mg/l 2.5m ACH 4 mg/l 2.5m ACH 1 mg/l 1m ACH 2 mg/l 1m ACH 4 mg/l 1m Coagulant Type & Dose ph 6. ph 7. Ambient ph Application Point Powdered Activated Carbon (PAC) Intake PAC PAC Intake PAC PAC PAC removal PAC Contactor Rapid Mix Flocculation PAC PAC removal B/W dist. Sedimentation Contact Time (min) varies 15 9 < Mixing poor excellent very good moderate none Developed by American Water Works Association with funds from the U.S. Environmental Protection Agency, Published 215 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 Developed by AWWA in partnership with RCAP and funded by USEPA, Published 215 4

5 Granular Activated Carbon (GAC): Post Filter Adsorber (PFA) Conventional treatment with additional GAC filter coagulant disinfectant Dist. rapid mix flocculation settling rapid media filtration GAC filtration disinfection & storage Application Post-Filter Adsorber EBCT (min) TOC Removal (%) months Media Life Media size Limitations 12x4 ES=.65 mm Cost/space/hydraulic head Oxidant compatibility Granular Activated Carbon (GAC): TOC Breakthrough Curves % biodegradable DOC C/C 5 15% non adsorbable Operation time, t Magnetic Ion Exchange (MIEX) Filtration Developed by AWWA in partnership with RCAP and funded by USEPA, Published 215 5

6 Contact Time (min) MIEX TOC Removal (%) Limitations MIEX Cost Footprint Hydraulic head Brine disposal Bio-Treatment Bio-treatment Riverbank Filtration Engineered Biological Filtration Contact Time Acclimation Period TOC Removal (%) Limitations > 3 days none 1-3 Land Availability Soil conditions 5 1 min > 2 months 1-3 Temperature Substrate availability No preoxidation 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 Developed by AWWA in partnership with RCAP and funded by USEPA, Published 215 6

7 Distribution System DBP Control Menu Shorten water age Optimize chlorination strategy Precursor removal Optimize existing treatment Install new treatment DBP removal after formation 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 DBPs (µg/l) Getting Started Reduce water age TTHM Cl 2 residual Chlorine Residual 2.5 Minimum Cl 2 residual Time (days) Developed by AWWA in partnership with RCAP and funded by USEPA, Published 215 7

8 Getting Started Reduce chlorine residual TTHM Cl2 residual Chlorine Residual DBPs (µg/l) 1.5 Minimum Cl2 residual Time (days) 2 25 Chlorination Strategies Booster Chlorination Primary Chlorination Prechlorination Raw water intake rapid mix flocculation sedimentation filtration Chloramine Conversion disinfection & storage distribution Prechlorination Primary Chlorination Booster Chlorination Oxidation of of Fe Fe & & Mn Mn Oxidation Biogrowth control control Biogrowth Long Long CT CT After TOC removal Pre-filter: longer filter runs Post-filter: bioremoval of TOC Keeps driving force low Developed by American Water Works Association with funds from the U.S. Environmental Protection Agency, Published 215 Chloramination 12 TOC = 2.5 mg/l Br = 5 µg/l Cl2 = 1.25 x TOC ph = 8. Temp = 15 C SUVA = 2. L/mg/min DBPs (µg/l) 1 8 TTHM MCL 6 HAA5 MCL NH3 4 TTHM HAA Time (hours) Developed by AWWA in partnership with RCAP and funded by USEPA, Published 215 8

9 Remote DBP Control Works in isolated areas of high DBPs TTHM aeration GAC/BAC WTP Low DBP High DBP Implement Remote DBP Control Remote DBP Control in Distribution Systems Water Treatment Plant Reservoir Stage 2 DBPR Site 8 μg/l TTHM Time 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 atm mol 1, 2 C) Chloroform (3. ±.1) x 1 3 Bromodichloromethane (1.6 ±.2) x 1 3 Chlorodibromomethane (8.7 ±.2) x 1 4 Bromoform (4.3 ±.3) x 1 4 Developed by AWWA in partnership with RCAP and funded by USEPA, Published 215 9

10 TTHM Aeration Strategies In-Reservoir Aeration Strategies Spray Surface External Aeration Strategies Tray / Packed Liqui Cel Tower Membrane Contactor Photos from a Full-Scale Installation 7.5-hp aerator installed within a 2 MG reservoir Full-Scale Data Following Implementation of Aeration Equipment Concentration (µg/l) 6 5 Before start of aeration 4 3 After start of aeration 2 TTHMs Distribution System Sample Site 75 1 HAAs Distribution System Sample Site 75 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 Developed by AWWA in partnership with RCAP and funded by USEPA, Published 215 1

11 Question What can you do if you have remote HAA5 problems? GAC/BAC Good removal of TTHM up to 1, Bed Volumes (BV) for EBCT of 1 min Higher BV for longer EBCT HAA5 removal by both adsorption & biological activities Completely eliminate Cl 2 residual % Removal 5 TTHM B. Johnson (27) 1 Min EBCT 2 Min 3 Min 2-3% TTHM removal after 3, bed volumes and 1 minutes EBCT GAC adsorption effective for ~1, bed volumes 4 35 Inflow 2 Bed Volumes HAA5 Adsorption breakthrough/ 2 Developing biological activity (µg/l) 15 Fully developed GAC Column 4 (1 min EBCT) 1 Initial adsorption biological activity Bed Volumes GAC/BAC Potential Benefits Passive treatment Minimal O&M Long bed life when compared to TOC removal installations Pressurized system Potential Challenges GAC disposal or reactivation TOC will govern carbon life expectancy May result in reduced loss in the distribution system Column tests should be conducted to better understand GAC capacity Developed by AWWA in partnership with RCAP and funded by USEPA, Published

12 GAC/BAC Rechlorination Reformation of DBPs Rate of reformation a function of DBP precursor concentration 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 Discussion Does your system have a location where remote DBP treatment may be warranted? Developed by AWWA in partnership with RCAP and funded by USEPA, Published