Characteristics of Trihalomethanes in Water Distribution System

Vol. 16 No.4Joumal of Souhoest Jiaotong Uniersiry (English Edinion)Oct. 2008Article ID: 1005-2429(2008 )04-0398-06Characteristics of Trihalomethanes in Water Distribution SystemZHAO Ming (赵明)' ，ZHANG Jie(张杰)'， ZHANG Xin-yu (张新瑜),ZHENG Shuang-ying (郑爽英)*，LI Xin(李欣)1. School of Municipal and Environmental Eninering, Harbin Instiue of Technology, Harbin 150090, China2. School of Enironmental Science and Eninering , Soushwest Jiaotong Uniersity, Chengdu 610033, China3. Department of Applied Chemistry , Harbin Instiute of Technology, Harbin 150090, ChinaAbstractTo investigate the charateristics of disinfection by-products (DBPs) in an actal water distibution systcm using the raw waterwith high bromide ion concentration, the composition and concentration of trihalomethanes (THMs) formed by chlorination of thewater in the presence of bromide ion were measured in a city water distribution system during one year. The resuts show thatbrominated THMs contibuted a great part (83% 89% ) to the index for additive toxicity (ATI) and resulted in the ATI of most ofthe samples exceeding WHO guideline standard for total THMs (TTHMs), especially during the summer (rainy season). Thisindicates that the chlorination of water in the presence of bromide ion leaded to high ratios of brominated THMs to TTHMs.However, a visible increase in the concentration of THMs with increasing residence time in the distribution system was not observed.Adinally , based on alernatives analysis , packed tower acration method is proposed to reduce THMs level of the finished waterleaving the treatment plant.Key words Water distribution system; Bromide ion; Disinfection by-products; Tribalomethanes; Index for additive toxicityIntroductionchloroform ( CHCl3 )，bromodichloromethane( CHBrCl2) (BDCM) , dibromomethane (CHBr2Cl)Most municipal water supply systems in China(DBCM), and bromoform ( CHBrg). The rate anduse chlorine for drinking water disinfection. Manyquantity of THMs formation increase as a function ofdisinfection by-products (DBPs) such as trihalometh-anes (THMs) and other halogenated DBPs are princi-chlorine , concentration of organic compounds, watertemperature , pH value , concentration of bromide ion,pally formed by the interaction between chlorine andand residence time in a distribution system(26). Sinceorganic compounds such as humic and fulvic acids ,which are naturally present in raw watern. Thethe beginning of 1990s， it has been reported thatTHMs most commonly present in drinking water areTHMs especially brominated THMs have high geno-toxic and/or carcinogenic potenciesl7ts. However,until quite recently no standards for THMs except forReceived 2008- 04-14chloroform were established in the Standards forFoundation item National High-Tech Research and Devel-Drinking Water Quality in China. Consequently chan-opment Program of China ( 863 Program ) ( No.ges in the concentration of chloroform in several2007AA06Z303)Biography ZHAO Ming (1962 -) , PhD. Her research inter-drinking water distribution systems have been report-est is in water supply engineeringd,中国煤化工ailable for other* Corresponding author. Tel.: + 86-451 -86282332; E-mil:THMzbzhm169@ yahoo. cn4MHCNMHGnd concentration口papur, u wiiuosivilZHAO Ming e al. / Characteritias of Tihalomethanes in Water Distribution System399of THMs in the water distibution system of a citywater is river water, in which higher pH value (7.2-were examined. The main objective was to investigate8.9), higher concentrations of ammonium nitrogenvariation characteristics of THMs, especially bromina-(0.2-1.5 mg/L) , higher concentrations of total dis-ted THMs, with different seasons in the water distri-solved solids (TDS) (300- -500 mg/L) and bromidebution system. Furthemore, the index for additiveion (0. 1-1.0 mg/L) are presented due to the pollu-toxicity was used to evaluate the behavior of bromina-tion of domestic and industrial wastewater and geolog-ted THMs in the water distribution system by usingical characteristics. In the treatment plant, a conven-World Health Organization ( WHO) guideline values.tional water treatment process was applied, and toremove ammonia in the raw water, prechlorination1 Materials and Methodswas also applied. The water was disinfected withchlorine so that the finished water was pumped from1.1 Water treatment flow in plantthe treatment plant with a free chlorine residual of0.5Fig. 1 shows the schematic diagram of the water-0. 75 mg/L.treatment plant (20000 m'/d) of a city. The raw12Raw watar oculation bsia +[ Selimataion basin F + Rapid sand filere j+ Reseroir1 PpelineCoagulantFig. 1 Schematic diagram of the water treatment planttreatment plant and each sampling station closed to1.2 Pipeline and sampling stationsmains after a five-minute flushing until the waterThe pipelines that are connected with water treat-reached a constant temperature, which indicates thatment plant were installed in 1990 and the material ofthe water comes from the mains. TO evaluate thethe pipeline is castiron pipe without lining. One sam-effect of seasonality on the concentration of eachpling station was set at the outlet of a finished waterTHM, samples were collected in each season. Tem-reservoir located inside the water reatment plant.perature , pH value, and total and free chlorine residu-Five sampling stations were selected considering theiral were measured at the time when the samples werelocations or residence time of water in the distributioncollected. Tap water samples were transported intosystem. The details of the sampling stations are giventhe cooler with ice packs in the laboratory, and thein Table 1.analysis of chlorofomm, BDCM, DBCM and bromo-Table 1 Information of sampling stationsform were made by using gas chromatography-massSampling station Distance from reservoir oule/m_ Diameter/ mmspectrometry (GC-MS) method.07004 2001.4 Calculation of index for additive toxicity5100007200The indexes for additive toxicity for chloroform,8 500brominated THMs and total THMs (TTHMs) were9 400calculated as follows by using WHO guideline values:1.3 Water sample collection and analysisIhlcrnfom =: Chorolorm.To mitigate the effects of daily cyclic water中国煤化工，temperature, samples were collected from taps at theMHC NM H Gandom'400Journal of Southwest Jiaotong UVniversity (English Edition)Imoa =aoolom +IE-TDMu,Fig. 2, the concentrations of TTHMs ranged from 91where C is the concentration of each THM and V isup to211 ug/L (with a mean value of 133 μg/L).the WHO guideline value of each THM. According to The mean concentrations of chloroform, BDCM, DB-the WHO's recommendation, Imaou should be lessCM, bromoform, and THMs in the warm seasonthan or equal to 1.were 1.5 to 2.5 times as high as those in the cold sea-son. However, we have to point out the fact that2 Results and DiscussionTHMs concentrations in the water leaving the treat-ment plant (location No. 1) showed a higher level in2.1 Characteristics of THMsthe summer season, which may be caused by higherSeasonal variation of the concentrations of chlor-temperature, higher pH value (7. 2-8.9) , and higheroform, BDCM, DBCM，and bromoform at eachconcentrations of ammonia (1.0-1.5 mg/L), COD .sampling station is summarized in Fig.2. In adition，(20- 30 mg/L) and bromide ion (0. 1-1.0 mg/L) ofthe temperature and chlorine residual of pipeline waterraw water.in each season is given in Table 2. As shown in■CHBr3 0 DBCM OBDCM QCHC35200卜 ■CHBr3 0 DBCM OBDCM因CHCB350 t00 ti0 t34Sampling point(a) Autumn(b) Winter含200■CHBr3 0 DBCM日BDCM QCHCI3200|CHBr3 口DBCM 口BDCM QCHC13150-当15(0100上0F日.日日3456(c) Spring(d) SummerFg.2 Seasonal variation of THMs along the pipelineTable2 Temperature and chorine residual in diferent seasonsnomenon may be that almost precursor organic materi-SasonAverage temperature/CAverage chlorineals had reacted with the chlorine after prechlorination.residua/(mg.L1)Consequently, not so much additional THMs wereAutumn12.50.85Winter1.00.78formed in the water distibution system even in theSpring10.80.69continued presence of chlorine residual ( Table 2).Summer18.00. 55The lower assimilable organic carbon ( AOC) concen-In addition, it is not observed that the THMstration (50- -70 μg/L) in the samples from locationconcentration increases with residence time of water inNo. :中国煤化工ter reservoir) alsothe distribution system. The major reason for this phe-supp:YHCNMHGZHAO Ming et al.1 Charcteristis of Trihalomethanes in Water Distribution Sysem4012.2 Characteristics of index for additiveThis indicated that the bromide ion of raw waterplayed an important role in THMs formation. In addi-toxicitytion, it was also found that in the distibution systemIn order to iluminate the behavior of brominatedthe ratio of Ig -M to Imow showed a quite steady val-THMs in the water distribution system, indexes forue (about 85%) in all seasons even in the continuedadditive toxicity for chloroform, brominated THMspresence of chlorine residual. Considering that bromi-and TTHMs were calculated by using WHO guideline nated THMs have high genotoxic and/ or carcinogenicvalues, and the results were shown in Fig.3. It waspotencies, and that THMs concentrations in the waterclear that brominated THMs contributed a great partleaving the treatrment plant (location No. 1) showed a(83% -89% ) to the ImmM. and resulted in the Imnom ofhigher level, it is suggested that some countermeas-most of the samples exceeding WHO guideline stand-ures should be taken in the treatment plant to reduceard, especially during the summer ( rainy season). THMs concentrations.囚Br-THMs 0 Chloroform2.0[口Br-THMs 0 ChloroformWHO standard.s t0H网.0一0.023Sampling point(b) Winter(a) Autumn0 Br-THMs囚Chloroform2.0「0 Br-THMs Chloroform2.0号1.豆1.00.5 t信0.0.64(C) Spring(d) SummerFig.3 Seasonal variation of indexcs for adive toxicity along the pipeline2.3Discussion on countermeasures forprior to distribution.The first method is the preferred method for con-reducing THMs concentrationstolling DBPs formation; however, it is difcult toThe basic methods that can be adopted for reduc-adopt biological treatment method because of low wa-ing the concentration of THMs are (1) removing pre~ter temperature during long cold season and high costcursor compounds before application of treatment( including construction, operation and maintenanceprocess ( such as using biological treatment, and en-costs). In addition, it is also dficult to adopthanced coagulation and fitration) ; (2) changing dis-enhar中国煤化工method, beauseinfectants ( such as using ozone, chlorine dioxide ,(1). aplied for remo-and monochloramine ) ; and ( 3 ) removing THMsTYHCNMHG402Joumal of Souhvest Jiaong Uniersty (English Edition)ving ammonia and iron in the raw water, (2) thiser than that by chlorine, but monochloramine alsomethod is only effective for natural organic materialproduces other DBPs, including cyanogens chloride.(NOM) removal, and (3) a high pH value reducesMoreover, monochloramine is a less powerful disin-treatment efficiency and a secondary treatment may befectant (2 000 to 100 000 times less effective) thanrequired. For changing disinfectants, the use of ozonefree chlorine for inactivation of E. coli and rotavirucscan lead to the increase of bromate ( with high carci-and should not be used as a primary disinfectantnogenicity) concentration through the oxidation ofalthough it can provide a residual disinfection withinbromide ion present in the raw water. The use ofthe distribution system.chlorine dioxide can inevitably produce other DBP'sFrom the viewpoint of technical feasibility,( chlorite and chlorate ) although chlorine dioxide doesprocesses for removing THMs prior to distributionnot oxidize bromide ions ( in the absence of sunlight)include activated carbon or membrane filtration or aer-to form brominated THMs. In addition, chlorine di-ation methods ( such as packed tower aeration and airoxide does not provide a persistent effct, which wilstripping). The characteristics of each treatmentaffect the eficiency of disinfection. The concentra-process for removing THMs prior to distribution aretions of THMs produced by monochloramine are low-summarized in Table 3.Table 3 Comparison of treatment processes for removing THMsOperation andRemoval ofemRemovalApplication rangeConstrnction costmaintenance costmaintenanceefciency /%/(Yuan.m-9)/(Yuan .m-3)condioncontaminantsSmall to largeActivated catbon30-6080-1000. 100.2.ComplexYesscale systemSmall to middleMembrane50-99200-3000.5-1.5Packed tower50-90 .1-200.01-0.02EaseOnly volatilizedacrationcontaninantsVaries with thetype of carbon andrnw water quality,composition andNotemembrane, designoperating condition,concentrationsparameters, structure life span of equipment,of THMs, etc.of buildings, etc.depreciation, etc.According to the results of altematives analysis ,3 Conclusionsit is difficult to adopt activated carbon or membraneSome conclusions can be drawn from this study:fitration processes due to high cost ( including con-(1) The concentrations of TTHMs both in thestruction，operation and maintenance costsrequirement of complex operation and maintenance.water leaving the treatment plant and in the distibu-Considering that almost precursor organic materialstion system showed high levels (91 up to 211 μg/L)had reacted with the chlorine after prechlorination, itespecialy during the summer season. This is consid-s recommended to use packed tower aeration tcered due to a high pH valuc and high concentrationsremove THMs prior to distribution because of the fol-of organic pollutants and bromide ion in raw water.lowing advantages:(2) The results of index for additive toxicity(1) high effective removal of THMs includinganalysis indicate that brominated THMs contributed abrominated THMslIJ ,great part (83% -89%) to ImM and then resulted in(2) low cost ( including construction, operation'THM中国煤化工_ting WHO guide-and maintenance costs), andlinesummer ( rainy(3) operating easily.season:YH.CNMHG。payatentintoZHAO Ming et al. 1 Charactristics of Trihalomehanes in Water Distributin System403brominated THMs formation in the areas where rawbyproduct formation after biologically assisted GAC treat-water normally has a high concentration of bromidement of water supplies with different bromide and DOCcontent[J]. Water Research, 1995, 29 (12): 2635 -ion, such as coastal or salt-alkaline areas.2642.(3) Visible increase in THMs concentration with[5] Chellam s. Effects of nanofilration on tribalomethaneresidence time in the distribution system was not ob-and haloacetic acid precursor removal and speciation inserved. The major reason of this phenomenon may bewaters containing low concentrations of bromide ion[J].that almost precursor organic materials had reactedEnvironmental Science & Technology, 2000, 34 (9):with the chlorine after prechlorination.1813-1820.(4) Considering that the prechlorination has to[6] Chen W J, Weisel C P. Halogenated DBP concenrationsbe applied, and almost all precursor organic materialsin a distribution system[J]. Journal of American Waterhave reacted with the chlorine after prechlorination,Works Association, 1998, 90(4): 151-163.packed tower aeration method is recommended for[7] World Health Organization. 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