[Sodium hypochlorite disinfection on effluent of MBR in municipal wastewater treatment process]

Sodium hypochlorite (NaClO) used in wastewater disinfection was assessed by examining its performances in lab fed by the effluent from a MBR treatment plant. The influence of sodium hypochlorite initial concentrations (0.5-3.0 mg/L) on the presence of indicator microorganisms (total coliforms, fecal coliforms), disinfection by-products (DBPs) concentrations and the acute toxicity were evaluated. Results indicate the total coliforms and the fecal coliform were 1500-2400 and 10-40 CFU/L, which is difficult to meet the present reclaimed water quality standards. A chlorine dose of 2.0 mg/L and contact for 1 h could achieve a 3 lg indicator bacteria reduction in MBR effluent samples. THMs (trihalomethanes) analysis indicated that concentrations of THMs increase with the raise of the active chlorine dose. After adding sodium hypochlorite 1 h the concentrations of trihalomethanes (THMs) were 16.22, 7.35 microg/L respectively and chloroform (TCM) accounted for 87% of THMs, the haloacetic acids (HAAs) was involved trichloroacetic acid (TCAA) 2.01 microg/L, dichloroacetic acid (DCAA) 1.58 microg/L and under the national limits. Luminescence bacteria acute toxicity analysis showed that the chlorinated effluent has higher inhibition rate (48%) in comparison to the control with a chlorine dosage of 3.0 mg/L. The results which could provide theoretical basis to production show that NaClO disinfection not only can inactivate microbe with the DBPs and acute toxicity of the effluent under the safety limits, but also meet the requirement of health and safety.