Removal of hydrophilic and hydrophobic dissolved organic matters in natural waters by alum coagulation

Abstract

The main objectives of this study were to remove hydrophilic and hydrophobic dissolved organic matters (DOMs) in natural waters by alum coagulation, to determine the trihalomethane formation potential (THMFP) created from hydrophilic and hydrophobic DOMs, and to study the reduction of THMFP resulting from the removal of hydrophilic and hydrophobic DOMs. Water samples were collected from Aung-Keaw Reservoir, Mae-Kuang Reservoir, and Mae-Sa River. DAX-8 resin was utilized to isolate DOM into hydrophobic and hydrophilic DOM fractions. According to the results from alum cosgulation experiments under conditions of pH values ranging from 5.0 to 7.0 and alum dosages of between 0 and 100 mg/L, it was found that the optimal conditions for DOM removal from water in Aung-Keaw Reservoir, Mae-Kuang Reservoir, and Mae-Sa River were at pH of 5.5 and dosage of 60 mg/L, pH of 6.0 and dosage of 40 mg/L, and pH of 6.0 and dosage of 40 mg/L, respectively. The percentage removal of the hydrophilic DOM fraction in water samples from Aung-Keaw Reservoir, Mae-Kuang Reservoir, and Mae-Sa River by alum coagulation at optimal condition were 33.0, 27.6, and 50.9 percent, respectively. The percentage removal of the hydrophobic DOM fraction in water samples from Aung-Keaw Reservoir, Mae-Kuang Reservoir, and Mae-Sa River were 79.6, 50.2, and 79.9 percent, respectively. THMFPs of raw waters from Aung-Keaw Reservoir, Mae-Kuang Reservoir, and Mae-Sa River were observed at 403.12, 235.87, and 112.36ug/L, respectively. THMFPs created from hydrophilic DOM fractions in water smaples from Aung-Keaw Reservoir, Mae-Kuang Reservoir, and Mae-Sa River were observed at 162.30, 124.61, and 77.00 ug/L, respectively, while THMFPs created from bhdrophobic DOM fractions were at 275.09, 156.82, and 62.58 ug/L, respectively. Alum coagulation at optimal condition could reduce THMFP created from hydrophobic fractions in water samples from Aung-Keaw Reservoir, Mae-Kuang Reservoir, and Mae-Sa River by about 68.5, 35.4 and 43.1 percent, respectively, while the percent reduction of THMFP creatd from hydrophilic fractions of about 43.1, 22.7, and 25.7 percent were observed, respectively. Finally, the EEM technique could be applied for preliminary classification of the major DOM fractions in water according to their peak positions and fluorescent intensities.