Monitoring Of MBR For Hospital Wastewater Treatment And Study On Ozone Disinfection Of MBR Effluent

Membrane bioreactor (MBR) has a high efficiency, its effluent and subsequent disinfection effect are good, and it can replace traditional wastewater treatment processes. The subject of this paper was to monitor the effluent quality related to the hospital wastewater treated by MBR, and study ozone disinfection for MBR effluent.The ammonia nitrogen concentrations of the MBR influent were between 16.1~90.0 mg/L, and the average removal efficiency was 97.9%. The COD concentrations of the influent were between 70.2~197 mg/L, and the effluent concentrations were below 26.8 mg/L steadily, with average removal efficiency of 85.1%. The average concentrations of the total bacteria, coliform and fecal coliform in MBR influent were 4.00×10~5 CFU/mL, 5.40×10~7 MPN/100mL and 1.70×10~7 MPN/100mL, respectively. The average concentrations of the total bacteria and coliform in MBR effluent after disinfection by chlorine dioxide were 129 CFU/mL and 218 MPN/100mL, respectively, and fecal coliform was not decteted. The corresponding average logarithmic removal efficiency of total bacteria was 4.6. During normal operation, the average effluent turbidity was 0.63 NTU, therefore MBR process could be used for hospital wastewater treatment effectively. The main indexes of the effluent could meet the requirements of Discharge Standard of Water Pollutants for Medical Organization (GB 18466-2005). Estimate of operation cost showed that the operation cost of MBR process was about 1.31 yuan/m3.To reduce the production of chlorinated disinfection by products, the disinfection effects of ozone on MBR effluent were studied and a method to monitor and analyse the liquid ozone concentration was established. The results showed that the liquid ozone concentration increased with the increasing gas phase ozone concentration accessing to the reactor. When ozone dosing ended, the decrease of the liquid ozone concentration slowed up.The experiments were carried out to study on the ozone disinfection for MBR effluent. When dosage of ozone was 8.48 mg/L with constantly dosing for 15 min and then close placement for 25 min, total bacteria was decreased from 1.02×10~4 CFU/mL to 625 CFU/mL, coliform was decreased from no less than 2.40×10~4 MPN/100mL to what it was not detected, and fecal coliform was not detected. The formula of the logarithmic removal efficiency of total bacteria vs the cumulative liquid ozone concentration accorded with the Chick-Watson disinfection model. It could reflect the ozone disinfection effect well.