REMOVAL oF HUMIC ACID FROM WATER RESOURCES USING AL aND FE SALTS DURING CONVENTIONAL COAGULATION

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.