Effects of ph and Dissolved Organic Matter on the Formation of Disinfection By-Products by Chlorination and Chloramination

Transcription

1 Proceedings of the 4th IASME / WSEAS Int. Conference on WATER RESOURCES, HYDRAULICS & HYDROLOGY (WHH'9) Effects of ph and Dissolved Organic Matter on the Formation of Disinfection By-Products by Chlorination and Chloramination SEZEN KUCUKCONGAR, MEHMET FAIK SEVIMLI *, ESRA YEL Selcuk University, Department of Environmental Engineering, 4275, Campus, Konya TURKEY ssari@selcuk.edu.tr, mfsevimli@selcuk.edu.tr *, etarlan@selcuk.edu.tr Abstract: - A major concern for water utilities is the formation of DBPs resulting from reactions between DOM and disinfectant. THMs and HAAs are the most common and have diverse toxicological effects. The formations of THMs and HAAs by chlorination with chlorine and chloramine at several DOM concentrations and ph s were investigated. Water sample was obtained from Istanbul Omerli Dam, isolated using a laboratory scale membrane system used for chlorination study at different organic matter concentrations. Diluted isolate samples were chlorinated according to UFC protocol. 24 hours after chlorination THM formation was in lower level at acidic ph, whereas at neutral or basic ph, higher concentrations of THMs formed. For all DOC conditions ultimate DBP levels were reached at 24 hours. Chloraminated samples slightly acidic (6) and slightly basic (8) ph resulted in lower THM from neutral ph. HAA formation in ph 6 and 7.2 were equal while lower at ph 8. Despite strong fluctuations ultimate levels were reached in the first 8 hours after chloramination. All formed DBPs except BF were considerably higher in chlorination. Effect of ph in the range of 6 to 8 was approximately the same in both disinfectants. Chloramination completes DBP formation reactions earlier and results in much lower quantities in terms of total THMs and HAAs. Key-Words: - Trihalomethanes, haloacetic acids, natural organic matter, chlorination, chloramination. 1 Introduction NOM exists in all surface waters and groundwaters as a result of complex biotic and abiotic reactions. A major concern for water utilities is the formation of DBPs resulting from reactions between dissolved portion (DOM) of NOM and disinfectant. Chlorination has played a critical role in removing pathogens and use of it as a disinfectant has come under scrutiny because of its potential to react with NOM and form chlorinated DBPs [1]. There has been an increasing concern about DBPs since Rook [2] as well as Bellar and Lichtenberg [3]. Altough there are various recently identified DBPs such as haloacetonitriles, halopropanones, haloketones, chloropicrin, chloral hydrate [4, 5], THMs and HAAs are the most common and their distribution depends upon several factors such as bromide concentration, ph, temperature, and quantity and characteristics of NOM [6]. THMs and HAAs have diverse toxicological effects. Especially THMs have been recognized as a carcinogenic halogenated by-product and potentially hazardous to human health [7, 8]. There are a lot of limitations imposed by EPA, European Union and WHO for DBPs and maximum limits has been decreased in new revisions recently. However, there is not any limitation for them in Drinking Water Standards of Water Pollution Control Regulations in many countries, although it should be. In this study, the formations of DBPs (THMs, HAAs) by chlorination with chlorine and chloramine at several DOM concentrations and ph s were investigated. The effects of ph and DOM concentration on the formation and speciation of DBPs were determined. 2 Material and Methods 2.1 Water Sample Water sample was obtained from Istanbul Omerli Dam, which has been used for the domestic and industrial water supply purposes in Istanbul metropolitan in Turkey. Reservoir volume at average water surface elevation is hm 3, reservoir area at this elevation is 23.1 km². All samples were kept in the dark at +4 C until analysis. 2.2 Isolation Water samples were isolated using a laboratory scale reverse osmosis membrane system, Filmtec reverse osmosis membrane which is thin film composite membranes packed in a spiral wound configuration. Isolation procedure was applied to concentrate the organic matter in the sample. Isolate was used for chlorination study at different organic matter concentrations. ISSN: ISBN:

2 Proceedings of the 4th IASME / WSEAS Int. Conference on WATER RESOURCES, HYDRAULICS & HYDROLOGY (WHH'9) 2.3 Experimental Methods Chlorination and Chloramination Diluted isolate samples were chlorinated according to UFC protocol [9] which simulates the average chlorination conditions in drinking water distribution systems in the USA and requires a free chlorine residual of 1.±.4 mg/l be maintained after one day of contact time [1]. Samples at the concentration of 2, 3 and 4 mg/l of DOC were prepared by diluting the isolate with ultra pure water and used in the experiments. Stock chlorine solution was prepared from sodium hypochlorite including 6-14% free chlorine. Monochloramine solution was prepared by mixing a free chlorine solution with an ammonium sulfate ((NH 4 ) 2.SO 4 ) solution at initial Cl:N ratio 5:1. Disinfectant was injected to bottles according to UFC. After the incubation period, bottles were opened and residual chlorine analysis was performed by the DPD colorimetric method according to Method 45-Cl G [11]. The residual chlorine remaining in the bottles was quenched with sodium sulfite prior to analysis for DBPs. 2.4 Analytical Methods DOC Analysis DOC analysis was performed by the high-temperature combustion method according to Standard Method 531 B [11] using a Shimadzu TOC-V CPH model TOC analyzer THMs Analysis THMs analysis were carried out according to EPA Method [12]. The method includes liquid-liquid extraction and gas chromatography (GC) measurement. Water samples were extracted with methyl-tert-buthyleter (MTBE) in 2 ml glass bottles with Teflon septa and screw caps. Reagent grade sodium sulfate was added to vials to increase ionic strength of the aqueous phase. Vials were shaked vigorously by hand four minutes. Solvent phase was transferred to GC vials by a disposable Pasteur pipette. THMs analysis were performed on a Agilent model 689 GC equipped with Agilent model 7683 autosampler, µ-electron capture detector (ECD) and HP- 5MS capillary column (3 m length,.25 mm i.d. and.25 µm film thickness, Agilent J&W Scientific). High purity helium (2.2 ml/min) was used as the carrier gas and high purity nitrogen (28.9 ml/min) was used as the make-up gas. GC operation conditions were as follows: Temperature program: 35 C for 22 min, 1 C/min up to 125 C. Injector temperature: 2 C, detector temperature: 29 C, injection volume: 1 µl. Calibration curves had at least seven points for four THMs (chloroform (CF), bromodichloromethane (BDCM), chlorodibromomethane (CDBM), bromoform (BF)). THMs calibration standards were purchased from Supelco, USA. High purity grade MTBE was purchased from Merck, Germany HAAs Analysis HAAs analysis were carried out according to EPA Method [13]. This method includes liquid-liquid extraction, methylation and GC measurement. Some modifications were used for this method [14]. For the extraction 2 ml glass bottles with Teflon septa and screw caps were used. ph was adjusted to less than or equal to.5 by adding concentrated sulfuric acid. After the sodium sulfate addition vial was shaken until almost all the chemicals dissolved. MTBE was added to extraction vials and shaken vigorously for three minutes by hand. For methylation procedure, solvent phase was transferred to a 15 ml graduated conical centrifuge tube using a Pasteur pipette. The centrifuge tubes were placed in a heating block at 5±2 C for 2 hours after adding 1 % sulfuric acid in methanol. This procedure was applied to convert HAAs to their methyl esters which can be separated chromatographically. After methylation procedure, sodium sulfate solution added to each tube and acidic aqueous methanol phase was discarded from tube with a Pasteur pipette. After this step, saturated sodium bicarbonate solution was added to tube and vortexed for several seconds at least four times to complete the neutralization reaction. Solvent phase was transferred to GC vials by a disposable Pasteur pipette. HAAs analysis were performed on the same GC introduced in Section above. High purity helium (1.8 ml/min) was used as the carrier gas and high purity nitrogen (35. ml/min) was used as the make-up gas. Temperature program: 35 C for 1 min, 5 C/min up to 75 C for 15 min, 5 C/min up to C for 5 min, 5 C/min up to 135 C for 2 min. İnjector temperature: 2 C, detector temperature: 29 C, injection volume: 1 µl. Calibration curves had at least five points and nine HAAs (monochloroacetic acid (MCAA), monobromoacetic acid (MBAA), dichloroacetic acid (DCAA), bromochloroacetic acid (BCAA), trichloroacetic acid (TCAA), dibromoacetic acid (DBAA), bromodichloroacetic acid (BDCAA), chlorodibromoacetic acid (CDBAA) and tribromoacetic acid (TBAA)). HAAs standards were purchased from AccuStandard, USA. MTBE, methanol was purchased from Merck at high purity. Other reagents were purchased from Merck at reagent grade purity. Fig.1 and Fig.2 represents GC µ-ecd chromatogram of THMs and HAAs respectively. ISSN: ISBN:

3 Proceedings of the 4th IASME / WSEAS Int. Conference on WATER RESOURCES, HYDRAULICS & HYDROLOGY (WHH'9) 3 Results and Discussion Fig.1. GC µ-ecd chromatogram of a 2 ppb standard of THMs. Fig.2. GC µ-ecd chromatogram of a 2-2 ppb standard of HAAs and Dalapon. 3.1 THMs and HAAs Formation After Chlorination THM and HAA results of chlorinated samples are presented in Table 1. As indicated in table, for all studied ph and DOC conditions, almost all THM and HAA compounds formed 24 hours after chlorination with some exceptions such as bromoform, MBAA, CDBAA and TBAA. THM formation was in lower level at acidic ph, whereas at neutral or basic ph, higher concentrations of THMs formed. Among the THMs, chloroform was the highest since it is the most stable one and formed first. The formation of THMs in chlorinated water is not due to reactions between chlorine and methane or chlorinated methanes. Instead, it is due to a complex reaction between chlorine, bromide and NOM [4]. Some THMs are intermediates, so these compounds can react with other THM compounds. For this reason, the variations were observed at bromodichloromethane and dibromochloromethane concentrations. Effect of ph and DOC on DBP formation is very similar for HAAs. Highest concentrations were observed at BCAA after 24 hours. Except mono- and di-haloacetic acids, most of mono- and di- halogenated DBPs are nonstable and these intermediate compounds turn out to be multi-halogenated acetic acids and other DBPs [4]. Changes of total THMs and HAAs with time are presented in Fig.3. For all DOC conditions ultimate DBP levels were reached at 24 hours in spite of some fluctuations at the beginning. Fig.3 represents the neutral ph condition. ph 6 and 8 had similar trends, all indicating increasing DBP formations with initial DOC. Table 1. THM and HAA formation at different ph and DOC conditions after chlorination Compound (ppb) ph 6 ph 7.2 ph 8 ph 6 ph 7.2 ph 8 ph 6 ph 7.2 ph 8 CF BDCM CDBM BF - a a a Total THM MCAA MBAA - a - a - a DCAA BCAA TCAA DBAA BDCAA CDBAA - a - a - a - a - a - a - a - a - a TBAA - a - a - a - a - a - a - a - a - a Total HAA Dalapon a Under detection limit ISSN: ISBN:

4 Proceedings of the 4th IASME / WSEAS Int. Conference on WATER RESOURCES, HYDRAULICS & HYDROLOGY (WHH'9) Total THMs conc., ppb Fig. 3. Impact of DOC concentrations on total THMs and total HAAs concentrations at ph 7.2 after chlorination. Variation of total THMs and HAAs 24 hours after chlorination with ph are summarized in Fig.4, respectively. Total THMs concentrations were increased with increasing ph at all DOC concentrations (Fig.4a). In general, a high ph results in a higher level of THMs but a lower level of HAAs [4, 15]. Variation of ph between 6 and 8 have no considerable effect on formation of HAAs at all DOC concentrations. 3.2 THMs and HAAs Formation After Chloramination THM and HAA results of chloraminated samples for 4 mg/l DOC are shown in Table 2. DOC variations were not studied because of much lower THM and HAA formations as compared to 4 mg/l DOC results of chlorination. Slightly acidic (6) and slightly basic (8) ph resulted in lower THM from neutral ph. Whereas HAA formation in ph 6 and 7.2 were nearly equal while lower ph 8. Total HAAs conc., ppb ph ph Fig. 4. The variation of total THMs and total HAAs concentrations occured after 24 hours at different ph. Table 2. THM and HAA formation at different ph after chloramination Compound (ppb) DOC 4 mg/l ph 6 ph 7.2 ph 8 CF BDCM.5 - a - a CDBM - a - a - a BF Total THM MCAA MBAA.2 - a - a DCAA BCAA TCAA DBAA BDCAA CDBAA - a - a - a TBAA - a - a - a Total HAA Dalapon a Under detection limit Changes of total THMs and HAAs with time after chloramination are indicated in Fig.5. THM and HAA formation trends were considerably different from chlorination case (Fig.3). Despite strong fluctuations ultimate levels were reached in the first 8 hours, indicating that the DOM-chloramine reaction is rapid, although chloramines requires longer time to complete disinfection. 9 9 ISSN: ISBN:

5 Proceedings of the 4th IASME / WSEAS Int. Conference on WATER RESOURCES, HYDRAULICS & HYDROLOGY (WHH'9) 8 ph 7.2 ph 6 ph 8 2 Chloramine Chlorine Total THMs, ppb CF BDCM CDBM BF Total THM b 8 4 Chloramine Chlorine Total HAAs, pp ph 7.2 ph 6 ph Fig. 5. Formation of total THMs and total HAAs during chloramination at different ph s at DOC of 4 mg/l. MCAA MBAA DCAA BCAA TCAA DBAA BDCAA Total HAA Fig. 6. Formation of THMs and HAAs compounds after 24 hours DOC 4 mg/l ph Comparison of Chlorination and Chloramination THM and HAA compounds after 24 hours chlorination and chloramination for 4 mg/l DOC at ph 7.2 (where DBP levels were highest) are compared in Fig.6. It is clearly seen that, under the same DOC, ph and residual chlorine conditions, all formed DBPs except BF were considerably higher in chlorination. Even some compounds such as BDCM and CDBM were formed only in chlorination, not observed, in chloramination. Effect of ph in the range of 6 to 8 was approximately the same in both disinfectants at the same DOC level. Highest THM formation was observed at neutral ph. When Fig.3 and 5 are compared, it may clearly be concluded that, THMs and HAAs formation continues to increase until 24 hours in chlorination while it is completed in several hours in chloramination. Then it can be said that, in chloramination, the system will have more time for hydrolysis as reported by Xie [4]. 4 Conclusion THM and HAA formations of chlorinated and chloraminated 2, 3 and 4 mg/l initial DOC concentrations at three different phs (6, 7.2 and 8) were investigated. Total THMs increased at neutral ph at the studied range, although some intermediates decreased. Whereas, total HAAs slightly changed with ph as well as some intermediates. It can be said that, THM formation was minimal for ph 6 while HAA formation was lower at ph 8 especially for higher initial DOC conditions. Strong differences are observed between chlorination and chloramination under same conditions. Chloramination completes DBP formation reactions earlier and results in much lower quantities in terms of total THMs and HAAs. 5 Acknowledgement This study is financially supported by the Scientific and Technological Research Council of Turkey under grant no 14 I 123. ISSN: ISBN:

6 Proceedings of the 4th IASME / WSEAS Int. Conference on WATER RESOURCES, HYDRAULICS & HYDROLOGY (WHH'9) References: [1] World Health Organization, Environmental Health Criteria 216, Disinfectants and Disinfectant By- Products, Geneva, 2. [2] Rook, J.,J., Formation of Haloforms During Chlorination of Natural Waters, Water Treatment Examination, 23, 234, [3] Bellar, T.A. and Lichtenberg, J.J., Determining Volatile Organics at Microgram-per-liter Levels by Gas Chromatography, Journal of the American Water Works Association, 66, , [4] Xie, Y., Disinfection By-Products in Drinking Water Formation, Analysis and Control, Lewis Publishers, USA, 24. [5] EPA, Controlling Disinfection By-Products and Microbial Contaminants in Drinking Water, Office of Research and Development, Washington DC, 21. [6] Minear, A.M. and Amy, G.L., Water Disinfection and Natural Organic Matter, Characterization and Control, ACS Symposium Series 649, American Chemical Society, Washington DC, [7] Krasner, S.W., McGuire, M.J., Jacangelo, J.G., Patania, N.L., Regan, K.M., Marco, A.E., Occurrence of Disinfection by-products in US Drinking Water, American Water Works Association Journal, 81, 8, 41-53, 21. [8] Uyak, V., Multi-pathway Risk Assessment of Trihalomethanes Exposure in Istanbul Drinking Water Supplies, Environment International, 32, 12-21, 26. [9] Summers, R.S., Hooper, M.S., Shukairy, H.M., Solarik, G., Owen, D., Assessing DBP Yield: Uniform Formation Conditions, American Water Works Association Journal, 88, 6, 8-93, [1] Kitis, M., Probing Chlorine Reactivity of Dissolved Organic Matter for Disinfection By- Product (DBP) Formation: Relations with Specific Ultraviolet Absorbance (SUVA) and Development of the DBP Reactivity Profile, Ph.D. Thesis, Clemson University, 21. [11] APHA, AWWA, WEF, Standard Methods for the Examination of Water and Wastewater, 21 st Edition, Washington DC, 25. [12] EPA, Method 551.1, Determination of Chlorination Disinfection By-Products, Chlorinated Solvents and Halogenated Pesticides/Herbicides in Drinking Water by Liquid-Liquid Extraction and Gas Chromatography with Electron-Capture Detection, Office of Research and Development, Ohio, [13] EPA, Method 552.3, Determination of Haloacetic Acids and Dalapon in Drinking Water by Liquid-Liquid Microextraction, Derivatization and Gas Chromatography with Electron Capture Detection, Office of Ground Water and Drinking Water, Ohio, 23. [14] Xie, Y., Analyzing Haloacetic Acids Using Gas Chromatography/Mass Spectrometry, Water Research, 35, , 21. [15] EPA, Alternative Disinfectants and Oxidants Guidance Manual, Office of Water, Washington, ISSN: ISBN: