Evaluation of Organic Compound Removal by Advanced Water Treatment System

Transcription

1 Evaluation of Organic Compound Removal by Advanced Water Treatment System D.Masuzaki*, S.Imanaka*, H, Hayashi* *Water Examination Laboratory, Osaka Municipal Waterworks Bureau, , Kunijima, Higashiyodogawa-ku, Osaka-shi, Osaka 33-24, JAPAN Abstract The removal and formation property of disinfection byproducts (DBPs) such as trihalomethanes (THMs) or haloacetic acids (HAAs) throughout the water purification process were researched focusing attention on formation potential (FP) by chlorination. For total organic halide (TOX), we have verified that 76% of TOX-FP contained in raw water can be removed by advanced water treatment. In TOX-FP, we succeeded in removing 8% of HAAs-FP in raw water. It has been suggested that in HAAs-FP, hydrophobic precursors contribute to formation of Tri-HAAs in which three halogen elements are combined with HAAs and are also considerably contribute to formation of chlorinated HAAs. After sand filtrated water from which hydrophobic precursors are considered to be nearly removed, it was verified that there is the tendency of a formation rate of brominated HAAs to increase. From this, it was considered that change in the precursors contained in water also causes formation property of HAAs to change. Key Words disinfection byproducts, Haloacetic acids, trihalomethanes, total organic halide, formation potential, advanced water treatment INTRODUCTION It is considered that chlorination in water treatment is imperative to eliminate the infectivity of pathogenic microorganism. On the other hand, it is known that chlorine reacts with organic matters in water to form disinfection byproducts (DBPs). Most typical DBPs formed by chlorine disinfection are thrihalomethanes (THMs) and haloacetic acids (HAAs). THMs includes chloroform, dichlorobromomethane, chlorodibromomethane, and bromoform. HAAs include mono-chloroacetic acid (MCAA), dichloroacetic acid (DCAA), trichloroacetic acid (TCAA), bromoacetic acid (MBAA), dibromoacetic acid (DBAA), tribormoacetic acid (TBAA), bromochloroacetic acid (BCAA), dibromochloroacetic acid (DBCAA) and bromodichloroacetic acid (BDCAA). For these organic DBPs, the U.S. Environmental Protection Agency (U.S.EPA) has specified the maximum permissible contaminant levels (MCL) for four types of THMs and the sum of five types of HAAs (MCAA, DCAA, TCAA, MBAA and DBAA) (Pontius, 23). The Ministry of Health, Labour and Welfare of Japan also set nine items including four individual THMs, total THMs and three types of HAAs (MCAA, DCAA, and TCAA) as water quality standard (MHLW, 23). For THMs and HAAs, there have been reports on formation of these items in the water purification plant (Rodriguez and Serodes et al., 27) and their behavior in water distribution systems (Rodriguez and Serodes, 24 ; Malliarou and Collins, ). According to the results of these research, it has been reported that there are seasonal variations in formation of DBPs and that precursors existing in raw water change seasonally. For these precursors, it is generally considered that natural organic matter (NOM) represented by humic matter is a large factor, but the effects of domestic wastewater, industrial wastewater, or agricultural effluent have also been pointed out (Galapate and Kitanaka,

2 1997). A reaction between these precursors and chlorine is largely affected by ph value, water temperature and reaction time. Moreover, there has also been a report that the types of DBPs to be formed differ depending on the physical property of the precursors (Liang and Singer, 23). In this report, we have evaluated the removal of DBPs in the water purification system focusing attention on formation potential (FP). We analyzed the removal process of total organic halides (TOX) and showed that THMs-FP and HAAs-FP had a large proportion in the total amount of TOX-FP. And we discussed the physical property of HAAs precursors and the formation property of HAAs, considering the types and amount of halogen elements in HAAs components. MATERIALS AND METHODS Sampling Figure 1 shows the advanced water treatment flow introduced into Osaka City. The investigation period was seven years starting from 2 to 26 and sample water of each process was taken every two months. Kunijima Water Purification Plant, Osaka Municipal Waterworks Bureau takes raw water from the Yodo River as a drinking water source. The Yodo River is one of the largest rivers in Japan and main water resource for 12 million people in Kansai area. The major features of this water purification plant are that two steps of ozonation before and after rapid sand filtration and granular activated carbon treatment are performed. Table 1 shows the quality of raw water during the investigation period. There is little change in the quality of raw water throughout the year excepting under peculiar weather conditions. Samples with residual ozone were deozonized with sodium thiosulfate solution, while those with residual chlorine were dechlorinated with L- ascorbic acid. Raw Water Coagulo Sedimentation Intermediate Ozonation Rapid Sand Filtration Post Ozonation Figure 1 Advanced water treatment flow SUVA (L/mg m) Analytical methods (±.6) Br All mesuaremwnts were followed to the method of (mg/l) (±.12) Standard Method for Drinking Water.(JWWA, 21) TOX was measured using a TOX analyzer (TOX-1, Mitsubishi Chemical). ph was adjusted by adding nitric acid to the sample bottle beforehand. HAAs (nine substances) was measured using gas chromatograph (GC) mass spectrometer (MS) (QP21, Shimadzu) after liquid-to-liquid extraction with methy-tert-butyl ether (MTBE), derivatized with diazomethane. THMs (four substances) were measured using electron-capturing GC (GC-21, Shimadzu). ph was adjusted by adding hydrochloric acid to the sample bottle beforehand. Chloral hydrate (Ch-Hyd) and dichloroacetonitrile (DCAN) were measured using GC/MS (QP21, Shimadzu) after liquid-liquid extraction using MTBE. Non-Volatite Soluble organic carbon (NVDOC) was measured using TOC analyzer (TOC-Vcsh, Shimadzu) according to combustion oxidation method. For TOX-FP and DBPs-FP samples, chlorine water was added so that approx. 1 mg/l remains as free chlorine after 24 hours under the conditions of ph7 and a temperature of 2 C. Then formed TOX and DBPs were measured as noted above. G A C Treated Water Table 1 Quality of raw water Max Min NVDOC (mg/l) UV4 (1/cm) Average (SD) 1.6 (±.34).32 (±.11)

3 RESULTS AND DISCUSSIONS TOX-FP The change of TOX-FP in raw water is shown in Figure 2. The mean value of TOX-FP during the investigation 6 period was 186 g/l, the maximum value was 4 g/l, and the minimum value was 97 g/l. Although 4 the maximum value was sporadically detected in 22, 3 significant changes were not observed in the results 2 other than that during the investigation period. For TOX-FP in the raw water, we need to compare the 1 weight per volume concentration of DBPs when all halogen elements of their compounds were converted Year into chlorine elements. Thus we obtained the Figure 2 Change of TOX-FP in raw water composition rate of DBPs-FP with respect to the overall TOX-FP by assigning the measurement results of individual chlorine-converted DBPs. The result was THMs-FP: 14.6%, HAAs-FP: 14.6%, Ch-Hyd-FP: 2.8%, and HAN-FP: 2.2% on average and the remaining 6.8% were unknown components. This result nearly agreed with the results of that the proportion of the revealed components of TOX formed by chlorine disinfection was approximately 3% (Kosh and Krasner, 1989). The composition rate changes year to year slightly, but the fact that the ratios of THMs and HAAs are high among the revealed compounds remained unchanged. Figure 3 (a) shows the behavior of the TOX-FP in the water purification system, while Figure 3 (b) indicates changes in the composition rate of each treatment process. The values in the figures indicate the mean values of respective substances during the investigation period. The removal rate of TOX-FP was 39% in the coagulo-sedimentation treatment, 29% in the intermediate ozone and sand filtration, and 8% in post-ozone and treatments, and 24% was un-removed and remained in the treated water. However, the composition rate of TOX-FP in each process was recognized to remain nearly the same. In other words, although the precursors of specific DBPs were not removed, those of respective DBPs were evenly removed. TOX-FP(μ g /L) in 2 THMs HAAs Ch-Hyd DCAN others THMs HAAs Ch-Hyd DCAN others TOX-FP(μg/L) 1 1 Int-Ozone Int-Ozone % 2% 4% 6% 8% 1% Figure 3 Transition of TOX-FP in water purification system : left (a) right (b) HAAs-FP The change of HAAs-FP in raw water is shown in Figure 4. The mean value of HAAs-FP during the investigation period was 42 g/l, the maximum value was 8 g/l, and the minimum value was 19 g/l. In the same way as the TOX-FP, significant change was not observed during the investigation period. Figure (a) shows the behavior of the HAAs-FP in the water purification system, while Figure (b) indicates changes in the composition rate of each process. The values in

4 the figures indicate the mean values of respective 2 substances during the investigation period. The figures show the change of five substances for which 1 drinking water MCL have been set by the U.S. EPA and others represents the sum of those obtained by 1 subtracting the noted five substances from the nine haloacetic acid substances measured this time. The removal rate of the HAAs-FP was 46% in the coagulo-sedimentation treatment, 28% in the intermediate ozone and sand filtration, and 6% in the post-ozone and treatments, and another 2% Year was un-removed and remained in the treated water. Figure 4 Change of HAAs-FP in raw water Moreover, from changes in the composition rate, the rate of TCAA decreased while the rates of MCAA, DBAA, and MBAA increased relatively as water treatment progressed to a latter part. For these changes, we tried to discuss the physical property of the precursors based on these changes in the HAAs-FP and the formation properties of HAAs in the water purification system by focusing attention on the number of halogen elements combined with HAAs and the types. HAAs-FP(μg/L) in 6 TCAA DCAA MCAA DBAA MBAA others TCAA DCAA MCAA DBAA MBAA others HAAs-FP(μg/L) Int-Ozone % 2% 4% 6% 8% 1% Figure Transition of HAAs-FP in water purification system : left (a) right (b) The halogen element number in formed HAAs HAAs with which three halogen elements are combined is represented as Tri-HAAs (sum of TCAA, BDCAA, CDBAA, and TBAA), HAAs with which two halogen elements are combined is represented as Di-HAAs (sum of DCAA, BCAA, and DBAA), and HAAs with which one halogen element is combined is expressed as mono-haas (MCAA, MBAA). Moreover, considering the fact that the mass of precursors in each-process-treated water differs, we used NVDOC as an index for making the effects of difference in the precursor mass uniform. In evaluation we used the mole number of HAAs formed by unit NVDOC. Figure 6 shows comparison of the amounts of formation of Di-HAAs and Tri-HAAs per unit NVDOC in each process. Compared to the results from raw water to intermediate-ozonation, the ratio of Tri-HAAs to NVDOC seems to decrease gradually in contrast to that of Di-HAAs. It was well known that hydrophobic matters are preferentially removed by the coagulo-sedimentation and ozonation (Marhaba and Van, 1998). From this result, it is possible to presume that hydrophobic precursors contribute to formation of Tri-HAAs. Moreover, it is also thought that change of precursors by ozonation may make it affected to form Tri-HAAs. After sand filtrated water, it is considered that there is not a great change in the formation rates of Di-HAAs and Tri-HAAs and also not a great change in the precursors.

5 2 2 MCAA MBAA Mid-Ozone % 2% 4% 6% 8% 1% DCAA CBAA BCAA % 2% 4% 6% 8% 1% TCAA TBAA DBCAA BDCAA Figure 6 Comparison between the amounts of formation of Tri-HAAs and Di-HAAs The types of halogen in formed HAAs HAAs with which only chlorine elements are combined is represented as Cl-HAAs (TCAA, DCAA, and MCAA) and HAAs with which bromine elements are combined is expressed as Br- HAAs (TBAA, DBAA, MBAA, CDBAA, DBCAA, and BCAA). Figure 7 (a), (b), and (c) show changes in the formation rates of Cl-HAAs (open) and Br- HAAs (shaded) in the water purification system by categorizing them based on the number of halogens combined with HAAs. Mono-HAAs remained nearly unchanged throughout the water treatment processes, while Br-HAAs rate increases in latter processes compared to raw water from the results of % 2% 4% 6% 8% 1% Figure 7 Changes in the formation rates of Cl- HAAs and Br-HAAs (Top: (a), middle: (b), bottom: (c)) Figure 8 Transition of the number of moles of Cl and Br elements combined to HAAs Di- and Tri-HAAs. In general, it is known that hypobromous acid is generated in oxidation of bromide ion with hypochlorous acid. When the reaction of hypobromous acid and that of hypochlorous acid are compared, the hypobromous acid reacts more preferentially than hypochlorous acid (Ichihashi and Teranishi, 1998). In pre-treatment of the formation potential analysis, the concentration of the hypochlorous acid is far higher than that of the hypobromous acid. However, it is considered that as the hypobromous acid reacts faster than the hypochlorous acid regardless of the mass of precursors contained in water, the rate of the Br-HAAs gradually increases through water purification system where the mass of the precursors is small. Figure 8 shows the change of the number of chlorine elements and that of bromine elements combined with HAAs per unit NVDOC for each process. The number of the chlorine elements reacting with HAAs decreases exponentially throughout the process while the number of the bromine elements reacting with HAAs was recognized to remain almost unchanged. Apart from the noted consideration, this fact suggests that the hydrophobic precursors that are considered to be easily removed in the coagulosedimentation or intermediate ozone treatment are apt to cause Cl-HAAs formation. Combined Number(μmol/L NVDOC) Combined Number of Cl Combined Number of Br Int-Ozone R.S.F

6 Comparison of HAAs and THMs formation As similar consideration to Fig.8 was examined about THMs to compare with HAAs, the result almost similar to HAAs was obtained. Especially while the number of bromine elements combined to THMs was not change so much in each process, the number of chlorine elements greatly changed. Moreover, Figure 9 shows the plot of the rates of chlorine and bromine elements reacted to form HAAs and those of THMs per unit NVDOC in each process. HAAs showed a wide range of the rate in comparison with that of THMs and no seasonal correlation was observed in its variations. It was shown that the effect of this is significantly attributable to the effect of Tri-HAAs in HAAs. From this, it is conceivable that the precursor of HAAs, especially Tri-HAAs, is more hydrophobic than that of THMs. Hua and David (27) led the similar consideration as the results of comparing formed DBPs-FP based on hydrophobicity and molecular size.thus, it is recognized that the amount and types of formed DBPs are affected by property of precursors throughout water purification system Int-Ozone & & Figure 9 Comparison between Cl and Br reacted to form HAAs and those reacted to form THMs CONCLUSIONS The proportion of the revealed compounds in TOX-FP is approximately 3% and the rate of these compounds remained almost unchanged throughout the water purification process. Ultimately, 76% of TOX-FP in raw water was removed by the water purification system. 8% of HAAs-FP in raw water was removed by the water purification system. Moreover, as the treatment progressed to a latter part, the rate of TCAA in HAAs-FP decreased significantly. When the formation of Tri-HAAs and that of Di-HAAs were compared, the Tri-HAAs reduced due to removal of the hydrophobic precursors. When the formation of Cl-HAAs and that of Br-HAAs were compared, the rate of Br-HAAs became greater as to Di-HAAs and Tri-HAAs in HAAs as the treatment progressed to a latter part. Moreover, the number of chlorine elements combined with HAAs formed per unit NVDOC

7 decreased significantly in the water purification process, but the number of bromine elements remained almost unchanged. When the rates of the chlorine and bromine elements reacted to form THMs and those of the chlorine and bromine elements reacted to form HAAs were compared, the HAAs showed wide range of the rate. Thus, it is conceivable that the precursor of HAAs is more hydrophobic than that of THMs. REFERENCES Galapate, R. P. & Kitanaka A Origin of Trihalomethane(THM) Precursors in Kurose River, Hiroshima, JAPAN Wat. Sci. Tech., 3(8), 1-2 HUA G. & Reckhow, D. A. 27 Characterization of Disinfection Byproduct Precursors Based on Hydrophobicity and Molecular Size, Environ. Sci. Technol., 41(9), Ichihashi K. & Teranishi K Brominated trihalomethane formation in halogenation of humic acid in the coexistence of hypochlorite and hypobromite ions. Wat. Res., 33(2), Kosh B. & Krasner, S. W Occurrence of distribution by-products in a distribution system. Proceedings, Annual Conference sponsored by American Water Works Association, Pt.2, Liang L. & Singer P. C. 23 Factors Influencing the Formation and Relative Distribution of Haloacetic Acids and Trihalomethanes in Drinking Water. Environ. Sci. Technol., 37(13), Malliarou E., Collins C., Graham N. & Nieuwenhuijsen, M. J. Haloacetic acids in drinking water in the United Kingdom. Wat. Res., 3(12), Marhaba, T. F., Van D. & Lippincott, R. L., 1998 Effects of ozonation vs. chlorination water treatment operations on natural organic matter fractions. Reports & Project Summaries, Departmant of Environment Protection, State of New Jersey. Pontius, F. W. 23 Update on USEPA s drinking water regulations. Journal AWWA, 9(13), 7-68 Rodriguez, M. J., Serodes, J. B. & Levallois P. 24 Behavior of trihalomethanes and haloacetic acids in a drinking water distribution system. Wat. Res., 38(2), Rodriguez, M. J., Serodes J. & Roy D. 27 Formation and fate of haloacetic acids(haas) within the water treatment plant. Wat. Res., 41(18), Standard Methods for the Examination of Water.21 Japan Water Works Association., Japan. The Ministry of Health, Labour and Welfare of Japan. 23 Water quality standard for drinking water. available at (accessed 3 June 211)