Background & Aims: Humic acid is a major agent in trihalomethanes (THMs) formation during chlorination process, which are known as carcinogens. The aim of this study were to investigate the removal of humic acid by three coagulants including PACl, alum and ferric chloride from water sources and their  effect on zeta potencial.

Materials & Methods: This study was conducted  experimentally in lab scale. Experiments were carried out in a batch reactor using a synthetic solution with humic acid concentration of 10 mg/l, pH 5, 7 and 9, and the coagulant dosages of 10, 20 and 30 mg/l (ferric chloride, alum and PACl, respectively). Also zeta potential and THMs formation reduction were evaluated under optimal condition  for humic acid removal.

Results: The results showed that under optimal dosages of the coagulants the highest removal efficiency was related to the ferric chloride with 89 %. Removal efficiency for PACl and alum were 88% and 81%, respectively. However, only the application of ferric chloride decreased the SUVA index down to the USEPA permissible limits (less than 2 L/mg m). Also in optimal condition pH, zeta potential and trihalomethanes values were gained more than 7, -15 mV and less than 50 ppb.

Conclusion: Ferric chloride can be used for treatment of water containing humic acid to decrease SUVA index down to the  permission ranges. But the use of aluminum salts as coagulants may lead to THMs formation. Chlorinated water treated with Ferric chloride results in notable reduction in the amount of trihalomethanes (ppb <80). Also, according to the zeta potential values, the adsorption phenomena was suggested as a dominant mechanism for the removal of humic acid using ferric chloride.

SOURCE: URMIA MED J 2016: 27(3): 247 ISSN: 1027-3727