Reduction of trihalomethane created from six fractions of dissolved organic matters in raw water supply by alum coagulation

Abstract

Reduction of THM created from six fractions of DOM by alum coagulation was studied in raw water supply from the reservoir of the Northern Industrial Estate, Lamphun province, Thailand. DOM was fractionated into six fractions including HPON, HPOB, HPOA, HPIB, HPIA, and HPIN by resin adsorption technique using the series of DAX-8, AG-MP-50, and WA-10 resins. Based on the results obtained, it was investigated that HPOA of 41.6%, HPIA of 20.5%, HPIN of 17.7%, HPON of 12.1%, HPIB of 4.8%, and HPOB of 3.4% were the fractions of DOMs in terms of DOC containing in filtered raw water. Accordingly, HPOA and HPIA fractions were found as the major DOM fractions which were 62% of total DOM. Regarding THMFP created from each DOM fraction, THMFP (HPOA) of 247.1 microgram/L, THMFP (HPIA) of 112.60 microgram/L, THMFP (HPON) of 68.0 microgram/L, THMFP (HPIB) of 67.9 microgram/L, THMFP (HPIN) of 64.90 microgram/L, and THMFP (HPOB) of 41.4 microgram/L were determined. However, the THMFP/DOC ratio of HPOA, HPIA, HPON, HPIB, HPIN, and HPOB were 101.0 microgram/mg, 93.3 microgram/mg, 95.6 microgram/mg, 242.5 microgram/mg, 62.1 microgram/mg, and 206.4 microgram/mg, respectively. According to the results from alum coagulation experiments under the conditions of pH values ranging from 5 to 8 and alum dosages of between 10 and 80 mg/L, it was found that the optimal condition for DOM removal was at the pH of 5.5 with an alum dosage of 40 mg/L. The percent reductions of THMFP created from each DOM fraction at the optimal alum coagulation were 57.1% for THMFP (HPOA), 53.7% for THMFP (HPON), 41.4% for THMFP (HPIN), 40.6% for THMFP (HPIB), 29.8% for THMFP (HPIA), and 15.2% for THMFP (HPOB). It can be concluded that alum coagulation could reduce THMFP (HPOA) more effectively than those of THMFP created from other DOM fractions. In addition, the EEM technique could be applied for preliminary classification of the major DOM fractions in water according to their peak positions and fluorescent intensities