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DBP Reduction Through Nanofiltration Membranes October 12, 2017 North Central Texas Chapter DAVID SLOAN, P.E., BCEE October Lunch Meeting

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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

210/12/2017 NCT Chapter TAWWA October Lunch Meeting

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

10/12/2017NCT Chapter TAWWA October Lunch

Meeting3

• Formation

• Health Effects – Identified as carcinogen

• Regulatory Limits

Trihalomethanes were first regulated DBPs.

10/12/2017 NCT Chapter TAWWA October Lunch Meeting 4

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

10/12/2017NCT Chapter TAWWA October Lunch

Meeting5

Case Study – Somervell County Water District

10/12/2017NCT Chapter TAWWA October Lunch

Meeting6

SCWD

SCWD sought surface water supply to relieve overpumping.

10/12/2017NCT Chapter TAWWA October Lunch

Meeting7

Wheeler Branch Reservoir

Channel Dam

Pump Station

Lake was constructed and filled.

10/12/2017NCT Chapter TAWWA October Lunch

Meeting8

Several treatment options were considered.

10/12/2017NCT Chapter TAWWA October Lunch

Meeting9

Membrane Filtration was pilot-tested w/Paluxy Water.

10/12/2017NCT Chapter TAWWA October Lunch

Meeting10

THM Formation Potential was tested during pilot.

10/12/2017NCT Chapter TAWWA October Lunch

Meeting11

Plant was constructed & started up well.

10/12/2017NCT Chapter TAWWA October Lunch

Meeting12

TTHM increased over time.

10/12/2017NCT Chapter TAWWA October Lunch

Meeting13

THM control options were considered.

• GAC Filtration (Adsorption)

• Ozonation

• Direct Coagulation

• UV Oxidation

• Magnetic Ion Exchange

• Nanofiltration

10/12/2017NCT Chapter TAWWA October Lunch

Meeting14

Promising alternatives were lab-tested

• Direct Coagulation

15

Microfiltration Membranes

Clearwells

Pump Station

Cl2 Cl2Coagulant

➢ Aluminum coagulants (PACL and ACH)

➢ TTHM reduction inadequate

Promising alternatives were lab-tested

• Ozonation

16

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

17

Microfiltration Membranes

Clearwells

Pump Station

Cl2

GAC

Cl2

➢ TTHM reduction inadequate

Promising alternatives were lab-tested

• Nanofiltration

18

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

10/12/2017NCT Chapter TAWWA October Lunch

Meeting19

WaterCl-

Na+

Large OrganicsCa++

Mg++

Nanofiltration was recommended alternative.

10/12/2017NCT Chapter TAWWA October Lunch

Meeting20

Original building design provided space for NF.

10/12/2017NCT Chapter TAWWA October Lunch

Meeting21

Results to date have indicated effective control of TTHM.

10/12/2017 NCT Chapter TAWWA October Lunch Meeting 22

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

10/12/2017NCT Chapter TAWWA October Lunch

Meeting23

• Periodic chlorine solution recirculation regimen implemented

• Sustainable NF

operation restored

NF has proven effective in TTHM reduction.

10/12/2017NCT Chapter TAWWA October Lunch

Meeting24

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Dis

infe

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Sample Date

SCWD Disinfection By-Product Results