Tailoring activated carbon for enhanced adsorption of disinfection byproduct precursors

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1 Tailoring activated carbon for enhanced adsorption of disinfection byproduct precursors Thien D. Do, M.S. Julian L. Fairey, Ph.D., P.E. Southwest AWWA Annual Conference October 12-14, 2014, Tulsa, OK

2 DBP Precursor Removal Enhanced coagulation Removes larger, more negatively charged NOM Activated carbon (GAC filtration or PAC) Removes smaller, neutrally-charged NOM Primary oxidants (e.g., ClO 2 ) Transforms NOM can alter reactivity, coagulation properties New processes Surface-modified carbon nanotubes

3 DBP Formation Potential Standard Methods 5710 B and D DBPFP used as an indirect measurement of DBP precursor concentrations Influent How to measure profiles for DBPs of interest? DBPFP DBPFP DBPFP GAC Filter Effluent at t 0 at t 1 at t 2

4 Standard Methods 5710-B and 5710-D Used to determine DBPFP Buffer: 10 mm phosphate ph: 7.0 ± 0.2 Disinfectant: free chlorine, chloramines, or others Reaction time: 7 days in the dark at 25 ± 2 C Chlorine residual after 7 days: 3-5 mg/l as Cl 2 Quenching agent: Na 2 SO 3 for THMs; NH 4 Cl for HANs DBPFP used as a proxy for DBP precursors Compare DBPFP of different water sources Measured before and after treatment to assess, improve, optimize DBP precursor removal

5 Drawbacks of SM 5710 Free chlorine and THMs DBPFP SM 5710: 3-5 mg/l (grey-shaded bar) TCM increases in this region (10-15%) 7-day chlorine residuals need be identical to accurately assess TCM precursor removal Note: Chlorine residual is free chlorine measured after a 7-day reaction time in the dark at ph 7 and 25 C, as specified by Standard Methods

6 Drawbacks of SM 5710 Free chlorine and HANs DBPFP SM 5710: 3-5 mg/l (grey-shaded bar) DCAN decreases at chlorine residuals greater than 1.5 mg/l OCl - and OH - destroys DCAN Difficult to assess HAN precursor removal Note: Chlorine residual is free chlorine measured after a 7-day reaction time in the dark at ph 7 and 25 C, as specified by Standard Methods

7 Research Objectives Develop a single method to assess organic precursors of DBPs in natural waters Time-consuming and labor-intensive THMs and HANs HAAs and N-nitrosamines (future work) Apply to assess DBP precursor removal Proof-of-concept: GAC filtration Other methods (coagulation, oxidation, sorption) Extend to improve/optimize/develop DBP precursor removal processes

8 Improving on Standard Methods Standard Methods used to measure DBPFP Buffer: 10 mm phosphate ph: 7.0 ± 0.2 Disinfectant: free chlorine and chloramines Reaction time: 7 days in the dark at 25 ± 2 C Chlorine residual after 7 days: 3-5 mg/l as Cl 2 Quenching agent: Na 2 SO 3 for THMs; NH 4 Cl for HANs Adapt to develop a DBP precursor concentration (DBP-PC) test Formation of THMs and HANs proportional to precursors Measure DBP-PC before and after treatment to assess efficacy of a DBP precursor removal process Facilitate improvement of DBP precursor removal processes

9 DBPFP by SM Buffer: 10 mm phosphate ph 7.0 HOCl/OCl - and NH 2 Cl Residual 3 to 5 mg/l 7-day reaction time Quenching: Na 2 SO 3 for THMs; NH 4 Cl for HANs Proposed DBP-PC Buffer: 20 mm carbonate ph 7.0 and ph 8.3 HOCl/OCl - and NH 2 Cl Dose 200 to 400 mg/l 7-day reaction time Quenching: Ascorbic acid

10 Trichloromethane (TCM) Left-side panel, free chlorine: TCM increases with CR Right-side panel, monochloramine Higher TCM formation at ph 7.0 (open symbols) compared to ph 8.3 Easier to differentiate precursor concentrations at ph 7.0 Monochloramine Free chlorine for assessing TCM Lower slope at higher CR

11 Dichloroacetonitrile (DCAN) Left-side panel, free chlorine: DCAN destruction by OCl - Right-side panel, monochloramine: No DCAN destruction Open symbols: ph 7.0 higher DCAN formation, can distinguish between waters tested Closed symbols: ph 8.3 lower DCAN formation, similar formation amongst the waters tested Monochloramine > Free chlorine for assessing DCAN

12 Fixed-bed GAC Reactors Effluent C 3 C 1 Coagulated and settled GAC GAC GAC water from DWTP Three lab-scale GAC columns in series DBP precursors: C 0 > C 1 > C 2 > C 3 Inline filter Settled water C 2 C 0

13 TCM: Residual vs. Dose Three GAC columns-in-series: Sampling Events A, B, and C DBPFP Left Panel: Standard Methods DBPFP region not useful for assessing TCM precursor removal High chlorine residual works Right Panel: DBP-PC Method High chloramine dose works and is easier experimentally

14 TCM: Breakthrough Three GAC columns-in-series: Sampling Events A, B, and C Left Panel Standard Methods DBPFP Increased sorption capacity on Day 80 relative to Day 50 (impossible) Right Panel DBP-PC Method 250 mg/l chloramine dose works well Breakthrough sometime prior to Day 50

15 DCBM: Residual vs. Dose Three GAC columns-in-series: Sampling Events A, B, and C DBPFP Left Panel: Standard Methods DBPFP region not useful for assessing DCBM precursor removal Higher free chlorine residual works better, but not well Right Panel: DBP-PC Method High chloramine dose works well

16 DCBM: Breakthrough Three GAC columns-in-series: Sampling Events A, B, and C Left Panel Standard Methods DBPFP Increased sorption capacity at Day 80 relative to Day 50 (impossible) Right Panel DBP-PC Method 250 mg/l chloramine dose works well Breakthrough sometime prior to Day 50

17 DCAN: Residual vs. Dose Three GAC columns-in-series: Sampling Events A, B, and C DBPFP Left Panel: Standard Methods DBPFP region not useful for assessing DCAN precursor removal High free chlorine residual not useful Right Panel: DBP-PC Method High chloramine dose works well!

18 DCAN: Breakthrough Three GAC columns-in-series: Sampling Events A, B, and C SM-DBPFP not useful for assessing DCAN breakthrough At 10 days, C1 > C2 > C0 > C3 High chloramine dose works well! At 10 days, C0 > C1 > C2 > C3 At 50- and 80 days, C0 C1 C2 C3 (breakthrough)

19 DBP-PC Test DBP-PC is an accurate indirect measurement of organic precursors of THMs and HANs Compare different GACs; rationally modify GACs Influent 250 mg/l Dose of Chloramines at ph 7 DBP-PC DBP-PC DBP-PC GAC Filter Effluent at t 0 at t 1 at t 2

20 Conclusions and Future Work DBPFP following Standard Methods Can be improved upon for assessing organic precursors of THMs and HANs DBP-PC test (our proposed method) High chloramine dose (250 mg/l) at ph 7.0 Carbonate buffer Quench with ascorbic acid Suitable for THMs and HANs Including bromine-substituted compounds Apply method for N-nitrosamines

21 Acknowledgments Participating Funding Agencies

22 Questions? Julian Fairey Thien Do

23 TCM: Dose vs. Residual Three GAC columns-in-series: Sampling Events A, B, and C DBPFP SM-DBPFP not useful for assessing TCM precursor removal High chlorine residual and high chloramine dose both work Chloramine dose easier experimentally

24 DCBM: Dose vs. Residual Three GAC columns-in-series: Sampling Events A, B, and C DBPFP SM-DBPFP not useful for assessing TCM precursor removal Only high chloramine dose works

25 DCAN: Dose vs. Residual Three GAC columns-in-series: Sampling Events A, B, and C DBPFP SM-DBPFP not useful for assessing DCAN precursor removal High free chlorine residual not useful High chloramine residual works well!

CE 370. Disinfection. Location in the Treatment Plant. After the water has been filtered, it is disinfected. Disinfection follows filtration.

CE 370. Disinfection. Location in the Treatment Plant. After the water has been filtered, it is disinfected. Disinfection follows filtration. CE 70 Disinfection 1 Location in the Treatment Plant After the water has been filtered, it is disinfected. Disinfection follows filtration. 1 Overview of the Process The purpose of disinfecting drinking