Evaluation of Trihalomethanes Formation Using Combined Process Coagulation/flocculation/membranes in Water Treatment

Abstract

The objective of this study was to evaluate the efficiency of the combined process coagulation/flocculation followed by ultrafiltration and a chlorination step using natural coagulant Moringa oleifera Lam in replacement to conventional treatment on the THM formation. Assays were carried out using Pirapó River Basin raw water, low turbidity (50 NTU). Coagulation/flocculation assays were initially performed in Jar-test using saline solution (NaCl – 1M) from M. oleifera seeds (MO) as coagulant with dosages range from 10 to 60 mg.L^-1 and polyaluminum chloride (PAC) as chemical coagulant with dosages range from 7 to 12 mg.L^-1. In membrane filtration step, ultrafiltration polyethersulfone membrane was used with 1bar operation pressure. Chlorination step was performed with sodium hypochlorite (1.5 mg.L^-1) during 30 min to 8 h. The parameters analyzed were color, turbidity, UV_254nm, dissolved organic carbon (DOC), total trihalomethanes (TTHM) and free chlorine. TTHM produced was evaluated by gas chromatography. The optimal dosage for PAC and MO coagulants were 9.5 and 50 mg.L^-1. After the chlorination step, TTHM residual increased lower using MO (9.3 µg.L^-1) than PAC (32 µg.L^-1), remaining in according to legislation (100 µg.L^-1). The coagulation/flocculation pre-treatment for both coagulants minimized the fouling formation in UF process.