Nitrogenous Disinfection By-Products Formation Potential from Molecular Weight Fractions of Natural Organic Matter

Transcription

1 Nitrogenous Disinfection By-Products Formation Potential from Molecular Weight Fractions of Natural Organic Matter Ina Kristiana, Jace Tan, Suzanne McDonald, Rino Trolio, Cynthia Joll, Anna Heitz and Jeffrey Charrois Curtin Water Quality Research Centre Perth, Western Australia

2 Curtin Water Quality Research Centre Strategic alliance between Water Corporation of Western Australia and Curtin University Curtin Resources and Chemistry Precinct

3 Outline of Presentation Background - Disinfection by-products (DBPs) - Natural organic matter (NOM) - Size exclusion chromatography (SEC) The Study - Aim - Methodology - Fractionation of NOM - Formation potential of nitrogenous DBPs Conclusions & Future Work

4 Disinfection By-Products (DBPs) Precursor materials + Disinfectant DBPs Organic: NOM Inorganic: Bromide, iodide Trihalomethanes (THMs) and haloacetic acids (HAAs) have been the most studied groups of DBPs Life-time exposure to DBPs associated with increased risk of cancer e.g. bladder cancer Currently, over 700 DBPs have been identified

5 Emerging DBPs Further advances in analytical chemistry Assessment of cytotoxicity, genotoxicity, mutagenicity, and carcinogenicity of identified DBP species Discovery of emerging DBPs of human health concern Limited study on occurrence and health effects Generally more carcinogenic and genotoxic Ranking and prioritisation of DBPs Nitrogenous DBPs (N-DBPs) considered to be of higher priority

6 Toxicity of N-DBPs Some N-DBPs identified as potent carcinogens higher potency than regulated DBPs halonitriles, haloamides, N-nitrosamines, nitrosamides, organic N-haloamines, haloquinones (Bull et al., 2006) Some N-DBPs are more cytotoxic and genotoxic than HAAs (Plewa et al., 2008)

7 Control of DBPs Removal of DBP precursors (NOM, bromide, iodide) prior to disinfection e.g. membrane filtration, activated carbon adsorption, ion exchange resin Change of disinfectant e.g. chloramine, chlorine dioxide, ozone Removal of DBPs following disinfection e.g. aeration, air stripping, biological activated carbon (BAC) Most effective: precursor removal NOM (practical & preventative)

8 Alternative Disinfectant Chloramine (monochloramine) is a popular alternative disinfectant more stable than chlorine forms lower concentrations of regulated DBPs forms more emerging DBPs? US: switch to chloramine to meet DBP regulations Australia: chloramine used for long distribution systems in remote locations All disinfectants produce DBPs Ozone e.g. bromate Chloride dioxide e.g. chlorite, chlorate RISK: risk trade-offs need to be considered when changing disinfectant

9 Removal of NOM Efficient removal of NOM requires a good understanding of NOM characteristics Chemical characteristics Functional group content, chemical structures, reactivity, elemental composition Physical characteristics Size or molecular weight (MW)

10 Size Matters NOM with high MW more amenable to removal by conventional coagulation treatment Low MW NOM difficult to remove using conventional coagulation treatment Low MW NOM contribute to bioavailable organic matter, promoting biofilm formation MW distribution of NOM affects membrane fouling Different potential to form DBPs for different MW NOM

11 Size Exclusion Chromatography (SEC) Tool for determination of (apparent) MW distribution of NOM Separation of NOM based on molecular size using chromatography column Signal response Time (min)

12 Preparative SEC Using SEC to separate sufficient quantities of MW fractions of dissolved NOM to allow for isolation of the MW fractions Further characterisation of individual MW fractions then possible Automated fraction collector HPLC system Preparative-scale SEC column Fractions collected in bottles through tubings

13 Aim of Study Fractionate NOM from selected study sites using preparative SEC Investigate the formation potential of N-DBPs from the collected MW fractions of NOM

14 Study Sites 3 study sites: South West Great Southern North West

15 Drinking Water Quality and DBPs: Western Australian Perspectives Selected study sites are key source waters in WA Unique challenges in providing safe drinking water High concentrations of dissolved organic carbon (up to 40 mg L -1 ) High concentrations of bromide and iodide (up to 2 mg L -1 ) Remote locations and high surface temperatures (use of chloramine as preferred disinfectant)

16 Methods Collect source water 1000 L Concentrate NOM by reverse osmosis ~ 1 L Dialysis of NOM concentrate Fractionation of NOM concentrate by Preparative-scale HPSEC Collection of MW fractions of NOM Chlorination and chloramination Of MW fractions of NOM Analysis of DBPs

17 Disinfection Experiments 8 mg L -1 Cl 2 4 mg L -1 NH 2 Cl 2 mg L -1 DOC 500 µg L -1 Br - 60 µg L -1 I - ph 7 2 mg L -1 DOC 500 µg L -1 Br - 60 µg L -1 I - ph 8 Reaction time: 72 hours Target disinfectant residual: 1-2 mg L -1

18 DBPs Analysed DBPs analysed using GC-MS-based methods HANs HNMs HAMs Monochloroacetonitrile Monobromoacetonitrile Dichloroacetonitrile Dibromoacetonitrile Trichloroacetonitrile Bromochloroacetonitrile Bromochloronitromethane Bromodichloronitromethane Dibromochloronitromethane Dichloronitromethane Trichloronitromethane Tribromoacetamide Chloroacetamide Bromoacetamide Nitrosamines N-Nitrosodimethylamine (NDMA) N-Nitrosoethylmethylamine (NEMA) N-Nitrosodiethylamine (NDEA) N-Nitrosodibutylamine (NDBA) N-Nitrosodipropylamine (NDPA) N-Nitrosopyrrolidine (NPYR) N-Nitrosopiperidine (NPIP) N-Nitrosomorpholine (NMOR) Dichloroacetamide Dibromoacetamide Trichloroacetamide

19 Characteristics of Source Waters Each source water has unique water quality characteristics Sample DOC (mg L -1 ) DON (mg L -1 ) SUVA 254 Bromide (µg L -1 ) Iodide (µg L -1 ) Great Southern North West South West NOM collected from each source water has different MW range Due to differences in climate, vegetation in surrounding catchment, factors influencing water inflow to reservoirs (e.g. rainfall, runoff, etcs)

20 Collection of MW Fractions of NOM Great Southern source water Elution time (min) Fraction Fraction 1 Fraction 2 Fraction 3 Fraction 4 Fraction 5 Fraction 6 Fraction 7 Apparent MW Range (Da) Blank

21 Collection of MW Fractions of NOM North West source water Elution Time (min) Fraction Fraction 1 Fraction 2 Fraction 3 Fraction 4 Fraction 5 Fraction 6 Apparent MW Range (Da) Blank

22 Collection of MW Fractions of NOM South West source water Time (min) Fraction Fraction 1 Fraction 2 Fraction 3 Fraction 4 Fraction 5 Fraction 6 Fraction 7 Fraction 8 Fraction 9 Apparent MW Range (Da) Blank >

23 Formation of HANs in NOM Fractions Concentration (um) Great Southern Chlorine Chloramine Concentration (um) North West Concentration (um) > MW range MW range South West Lower concentrations of HANs formed in chloramination No clear trends in the formation potential of HANs from MW fractions of NOM MW range

24 Formation of HNMs in NOM Fractions Concentration (um) Great Southern Chlorine Chloramine Concentration (um) North West MW range MW range Concentration (um) South West Higher concentrations of HNMs formed in chloramination No clear trends in the formation potential of HNMs from MW fractions of NOM > MW range

25 Formation of HAMs in NOM Fractions Concentration (um) Great Southern Chlorine Chloramine MW range Concentration (um) North West MW range Concentration (um) > South West Higher concentrations of HAMs formed in chloramination No clear trends in the formation potential of HAMs from MW fractions of NOM MW range

26 Formation of N-Nitrosamines in NOM Fractions Concentration (nm) Chlorine Chloramine Great Southern MW range Concentration (nm) North West MW range Concentration (nm) > South West Higher concentrations of N- nitrosamines seemed to be formed from NOM with apparent MW of < MW range Higher concentrations of N- nitrosamines formed in chloramination

27 Chlorination vs. Chloramination HANs consistently formed at higher concentrations in chlorinated samples DHAN most frequently detected, measured at highest concentrations HNMs and HAMs mostly formed at higher concentrations in chloraminated samples Dichloro- species measured at highest concentration N-nitrosamines consistently formed at higher concentrations in chloraminated samples NDMA measured at highest concentration in most samples Variations in species and group distribution in chlorination vs. chloramination

28 DBP Formation & NOM Characteristics Higher N-nitrosamines formation potential for NOM with lower apparent MW (< 1 ) No clear trend in the formation of halogenated N-DBPs from MW fractions of NOM Size of NOM has little influence on formation potential of halogenated N-DBPs N-containing NOM reported to be precursors of N-DBPs Functional groups within NOM determines formation potential of N-DBPs NOM of any size may contain these important functional groups

29 Implications for Water Treatment Removal of low MW NOM will minimise the formation of N-nitrosamines N-DBPs are formed to a greater extent in chloramination Risk trade-offs for using chloramine as alternative disinfectant Improvements in conventional drinking water treatment to minimise the formation of DBPs Every source water has different potential to form emerging DBPs Case-by-case consideration to optimise drinking water treatment to minimise formation of DBPs

30 Current & Future Work Study the occurrence of N-DBPs in drinking water distribution systems in WA, especially in chloraminated distribution systems ARC Linkage Project: Advanced Water Treatment Techonologies to Minimise Nitrogenous Disinfection By-Products in Drinking Water: Understanding the Role of Organic Nitrogen

31 Acknowledgements CWQRC Team Geoff Chidlow, Deborah Liew, Andrew Chan, Bradley Allpike Water Corporation Australian Research Council GHD

32 THANK YOU!