高度淨水處理를 위한 HCPAC-MBR 工程에서의 소독부산물 低減에 관한 硏究
(A) Study on Removal of Disinfection By-products(DBPs) in High Concentration Powdered Activated Carbon Membrane Bio-reactor(HCPAC-MBR) For Advanced Water Treatment
고도정수처리 HCPAC-MBR 공정 소독부산물 수처리;
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The conventional water treatment plant(CWTP) was exhibited many problems for CWTP for removing high concentration of organic matter from source water. Especially, some modifications for their existing treatment processes are needed to achieve the reduction of disinfection by products (DBPs) including haloacetic acids(HAAs) and tirhalomethanes (THMs) generated during chlorination. HAA and THM did not reach the levels of risk. However, it is difficult to achieve compliance with the new regulations based on HAAFP and THMFP(HAA 60㎍/L, THM 80㎍//L by the Stage 1 D/DBPs Rule(2001)). In this study, a pilot scale experiment was conducted to evaluate the performance of a membrane bio-reactor filled with high concentration powdered activated carbon. This hybrid system has high potential to substitute for existing GAC or O_(3)/BAC process at the drinking water treatment train. The system was installed at CWTP located in down stream of Nakdong river basin, Korea. Effluent of rapid sand filter was used as influent of the system which consists of PAC bio-reactor, submerged MF membrane module and air supply facility. PAC concentration of 40g/L was maintained at the beginning of the experiment. The PAC has not been changed during the operation periods. Membrane was hollow fiber type with pore size of 0.1㎛ or 0.4㎛. From the experimental investigation, Following results were obtained. The coconut shell PAC was estimated to be proper adsorbent for standard solution(KHP: Potassium hydrogen phthalate) in pure water. Its Freundlish coefficient, K value was 11.69 and 1/n, 0.3921 for DOC. Design and operation parameters were obtained from the bench scale experiment, such as PAC concentration (40g/L), the Flux (0.36 m/day) and intermittent suction cycle (12 min. suction and 3 min. idling) and backwashing time (3min). The molecular weight (MW) distributions of influent and effluent showed similar trends, and both exhibited higher relative fractions for the lower MW range. The fractional rejection(FR) of effluent was exhibited about 93% from a MW of approximately 200 to a MW of 2300. The MW structure of influent was exhibited hydrophobic NOM 15.0%, transphilic NOM 10.6%, hydrophilic NOM 74.4%. Preferential removal of hydrophobic NOM fraction was achieved by HCPAC-MBR system compared to transphilic and hydrophilic NOM fraction. The relative fractions of hydrophobic and hydrophilic NOM decreased and increased respectively, after HCPAC-MBR processes. HAA and THM removal could be maintained at about 80~90% without any trouble and then tremendous reduction of HAA and THM reactivity higher than 52%. The removal of HAA formation potential(FP) and THMFP was exhibited about 70.5% and 67.6% respectively. From two years operation, it is clear that the PAC membrane bio-reactor is highly applicable for advanced water treatment under recent situation of more stringent DBPs regulation in Korea.