Trihalomethane formation potential of DOM fractions in water production by in-line coagulation ceramic membrane microfiltration

Abstract

The aims of this research were to investigate the trihalomethane formation potential of DOM fractions in water production by in-line coagulation with ceramic membrane microfiltration. Raw surface water was collected from Ping River water, Chiang Mai, Thailand which utilized as main raw water source for water supply production in this province. In-line coagulation with ceramic membrane filtration was conducted both in batch and continuous experiment. Polyaluminium chloride was used as coagulants. The reduction efficiency of DOM (THMs precursors) by in-line coagulation with ceramic membrane filtration was investigated. DOM is a complex mixture of hydrophilic and hydrophobic organic materials which varies in size, functional groups and reactivity. Thus, the characterization of DOM in water samples was investigated. The fractionation technique was utilized to separate DOM into HPIA, HPIN, HPIB, HPOA, HPOB and HPON fraction by using DAX-8, WA-10 and AG-MP-50 resin. In addition, the chemical classes of DOM in water samples was investigated by using GC/MS pyrolysis technique. From the results, it was found that in-line coagulation with ceramic membrane filtration can be utilized to reduce DOM from this water source and the reduction efficiency was increased with the increasing of PACl dosage. Percent DOC, UV-254 and THMFP reduction by in-line coagulation with ceramic membrane filtration at the optimal dosage (40 mg/L) was found in the range of 40-48%, 67–75% and 58–68%, respectively. In addition, the results of continuous experiment of in-line coagulation with ceramic membrane filtration showed that this combination processes can be operated in a long term operation without the significantly decreased of performance. For the results of resin fractionation, it was found that HPIA and HPOA fractions were the major fraction (38-40% and 24-29%, respectively) and main precursors of THMs in this water source. However, the highest specific THMFP value was found in HPOB and HPIB fraction which indicates that these two fractions had a high ability to form THMs. In-line coagulation with ceramic membrane filtration was found to reduce DOM mostly in term of HPOA fraction (>60%). Furthermore, it was found to highly reduce HPOB and HPIB fraction which difficult to reduce by conventional coagulation. From the investigation of chemical classes of DOM, it was found that aliphatic hydrocarbon was the major chemical classes in all DOM fractions (>48%). However, chemical classes of DOM in each DOM fraction provided the different ability to form THMs. The results showed that aliphatic hydrocarbon in HPIA, HPIN, HPOA and HPON had a low ability to form THMs but those in HPIB and HPOB fraction had a high ability to form THMs.