Reduction of trihalomethanes using combined process coagulation/floculation/membranes in water treatment

The chlorine used in the water disinfection step has been responsible for producing byproducts such as trihalomethanes (THM) in the presence of organic substances. For this reason several studies have been performed in order to develop alternative treatments to minimize the formation of these compounds. Therefore, the objective of this study was to evaluate the efficiency of the combined process coagulation / flocculation + membrane filtration (MF and UF) + chlorination using natural coagulant Moringa oleifera Lam in replacement to conventional treatment on the formation of THM. Assays were carried out using Pirapó River Basin raw water, low turbidity (50 NTU). Coagulation/flocculation assays were initially performed in Jar-test using different preparations: crude extract (MO) and hexane extraction (MO(hex)) with dosages range from 10 to 60 mg.L^-1. In membrane filtration step, microfiltration membrane of poly (imide) and ultrafiltration membrane of poly (ether sulfone) were used, these being in the form of hollow-fibers from engineering polymers, produced by the company PAM-Membrane Sectionals (COPPE-UFRJ, Rio de Janeiro-RJ/Brazil). Chlorination step was performed with sodium hypochlorite (1.5 mg.L^-1) for contact times of 30 minutes to 8 hours. The parameters analyzed were color, turbidity, TTHM, UV254nm, COD and free chlorine. TTHM produced was evaluated by gas chromatography. Among the results obtained, statistical analysis indicates that the coagulant preparations are statistically different between individual dosages, with optimal dosages for MO and MO (hex) of 50 mg.L-1 and 30 mg.L-1, respectively. For both coagulant preparations, membrane filtration reduced the amount of MON, with a consequent significant decrease of TTHM.