Coagulation of THM by Alum

The Sixth PSU Engineering Conference 8-9 May 2008 Influence of Coagulation with Alum and Cationic Polymers on the Formation of THMs Vorapot Kanokkantapong 1* Bunyarit Panyapinyopol 2 Suraphong Wattanachira 3 Porntip Wongsuchoto 4 1* Department of Environmental Health, Faculty of Public and Environmental Health, Huachiew Chalermprakiet University, Samutprakarn 10540 2 Department of Sanitary Engineering, Faculty of Public Health, Mahidol University, Bangkok 10400 3 Department of Environmental Engineering, Faculty of Engineering, Chiangmai University, Chiangmai, Thailand 50200 4 National Center of Excellence for Environmental and Hazardous Waste Management, Chulalongkorn University, Bangkok 10330 E-mail: [email protected]* Abstract In the water treatment plant, coagulation is one of the most applied processes due to the effective to remove colloidal materials and could also be applied to controlling the disinfection by-products (e.g. trihalomethanes, THMs). This paper revealed that there was possibility in using coagulation in controlling the formation of THMs by using alum with three types of cationic polymer; cationic polyacrylamide (CatPAM), polydiallyl dimethyl ammonium chloride (DADMAC), and epichlorohydrin dimethyl amine (EpiDMA). Water sample from Bangkhen Water Treatment Plant, Bangkok, was found the proper condition of the coagulation-flocculation process obtained at pH of 5.5. The highest efficiency in the removal of THM formation potential could be ordered from high to low as: alum with DADMAC (39%), alum with EpiDMA (32%), alum with CatPAM (21%), and alum alone (18%). In addition, hydrophilic neutral (HPIN) and hydrophobic acid (HPOA) which were the most abundant organic fractions in this watercourse could be removed by using alum or alum with cationic polymers. Keywords: THMs, Coagulation, Cationic polymer, Alum Introduction It is generally accepted that surface water is contaminated with dissolved organic matters, which are derived both from natural degradation processes and, to a higher extent, from human activities. In the water treatment facilities, surface water often passes through a series of treatment steps including the final disinfection process before the distribution through the municipal pipeline network. During the disinfection process with chlorine or chlorine derivative compounds such as hypochlorites, such organic contaminants could lead to the generation of potential carcinogenic disinfection by-products (DBPs), e.g. trihalomethanes (THMs), haloacetic Acids (HAAs), and haloacetonitriles (HANs) [1,2]. THMs, in particular, are a series of chlorinated and brominated methanes which brominated methanes was reported to have more toxicity than chlorinated methanes. Past research has therefore focused on the development of the removal techniques of organic precursors for these compounds. Although conventional water treatment processes (coagulation with alum, sedimentation and filtration) were often designed and operated for turbidity and color removal, and not targeted on the organic precursor removal, they were illustrated to have potential for the removal of some organic contaminants [1,3,4,5]. Coagulation with alum was reported to be quite effective in removing hydrophobic and high molecular weight organics [1]. Past reports demonstrated that enhanced coagulation, process of improving the removal of DBP precursors in a conventional water treatment plant could be an effective method for organic matter removal [6,7,8,9]. This technique has therefore been proposed as a best available technology of the stage 1 of the D/DBP Rule and is a valuable means of controlling DBP formation without requiring significant capital investments [10]. Bolto et al. (1999) [11] stated that coagulation by polymers provided several advantages over inorganic coagulants particularly for organic matter removal as the operation with polymer required significantly less resources. Moreover, this technique was relatively independent of pH, giving product water with a lower level of dissolved ions, and also a lower sludge volume could be obtained. Coagulation by combination of alum and polymer technique could be employed to improve THM precursor removal [11,12,13]. This work was set out to investigate the mechanism of the coagulation with polymers in controlling the generation of THMs in the chlorination process which provided an insight into the use of cationic polymers for the removal of THM organic precursors. The water samples were taken from Bangkhen water treatment facility in Bangkok,

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Coagulation of THM by Alum