DBP Reduction Through Nanofiltration Membranes
October 12, 2017
North Central Texas Chapter
DAVID SLOAN, P.E., BCEE
October Lunch Meeting
Nanofiltration is effective for removing THM Precursors.
•DBP Background
•Treatment/Mitigation Alternatives
•Case Study
•Lessons Learned
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Disinfection Byproducts Result from Reactive Chemicals
• Chlorine + Organics – Trihalomethanes (THMs) and
Haloacetic Acids (HAAs)
• Chlorine dioxide decay – Chlorite
• Ozone + Bromide – Bromate
Not (yet) regulated:
• Chloramine + Organics – Nitrosamines
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• Formation
• Health Effects – Identified as carcinogen
• Regulatory Limits
Trihalomethanes were first regulated DBPs.
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TotalTrihalomethane
Rule
Phase I DBP Rule
Phase II DBP Rule
Several Approaches have been used to control THMs.
• Alternative Disinfection
• Precursor Removal
• THM Adsorption
• THM Stripping
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Case Study – Somervell County Water District
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SCWD
SCWD sought surface water supply to relieve overpumping.
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Wheeler Branch Reservoir
Channel Dam
Pump Station
Lake was constructed and filled.
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Several treatment options were considered.
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Membrane Filtration was pilot-tested w/Paluxy Water.
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THM Formation Potential was tested during pilot.
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Plant was constructed & started up well.
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TTHM increased over time.
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THM control options were considered.
• GAC Filtration (Adsorption)
• Ozonation
• Direct Coagulation
• UV Oxidation
• Magnetic Ion Exchange
• Nanofiltration
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Promising alternatives were lab-tested
• Direct Coagulation
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Microfiltration Membranes
Clearwells
Pump Station
Cl2 Cl2Coagulant
➢ Aluminum coagulants (PACL and ACH)
➢ TTHM reduction inadequate
Promising alternatives were lab-tested
• Ozonation
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Microfiltration Membranes
Clearwells
Pump Station
O3Coagulant Acid / H2O2
Cl2Caustic
➢ TTHM reduction marginal
➢Required pH reduction
➢Bromate compliance marginal
Promising alternatives were lab-tested
• GAC Adsorption
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Microfiltration Membranes
Clearwells
Pump Station
Cl2
GAC
Cl2
➢ TTHM reduction inadequate
Promising alternatives were lab-tested
• Nanofiltration
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Microfiltration Membranes
Clearwells
Pump Station
Cl2 Cl2
Break Tank
Nanofiltration Membranes
MF Filtrate
NF Permeate
➢ High TTHM reduction demonstrated
Nanofiltration Process is similar to Reverse Osmosis
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WaterCl-
Na+
Large OrganicsCa++
Mg++
Nanofiltration was recommended alternative.
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Original building design provided space for NF.
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Results to date have indicated effective control of TTHM.
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Start-up of NF System
NF was susceptible to organic fouling.
• Cartridge Prefilters pressure
• Biological Growth in MF system
• Late chlorine addition allowed bacterial growth in system
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• Periodic chlorine solution recirculation regimen implemented
• Sustainable NF
operation restored
NF has proven effective in TTHM reduction.
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Dis
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SCWD Disinfection By-Product Results
