Experimental Study On Low-strength Domestic Wastewater Treatment By Anoxic/Aerobic Membrane Bioreactor

Currently, domestic wastewater has become a major factor affecting the quality of urban water environment. Shortage of water resources and water pollution are the limitation of the sustainable development of modern society. There were a large number of domestic wastewater with low-strength of organic substance and C/N ratio is relatively smaller, in China's southern city. It is limitary that low-strength domestic wastewater was treated using conventional activited sludge process.On the basis of existed nitrogen treatment processes, an anoxic-aerobic membrane bioreactor(A/O-MBR) was chose to treat the low-strength domestic wastewater. It meaned to make full use of nitrification and denitrification as well as advantages of membrane bioreactor (MBR) during the treatment. In this paper, low-strength doemestic wastewater was treated using A/O-MBR and made the effluent quality reached "the Water quality standard for urban miscellaneous water consumption" promulgated by the ministry of construction. Experiments were carried out to investigate the operation efficiency, the characteristic of sludge, and law of sludge growth. By optimizing the operation condition, a reference and basis of design was provided for project practice.In the case of no discharge of excess sludge, the experimental study indicated that under the condition of mixed liquor suspended solids (MLSS) of 3500mg/L to 5500mg/L, pH of 6.7-8.7, dissolved oxygen(DO) less than 0.5mg/L in anoxic area, DO of 1.5mg/L to 2.5mg/L in aerobic area, and sludge return ratio of 200% to 300%, the average concentration of effluent's COD_cr, NH₃-N, SS, turbidity were 17.53mg/L, 1.8mg/L, 1.95mg/L, 0.21NTU, with average removal efficiencies of 91.2%, 94.9%, 96.5%, 99.4% respectively. It meet the demand of wastewater reuse, reached "the water quality standard for urban miscellaneous water consumption". It is feasible to treat low-strength domestic wastewater using the technics.A/O-MBR system had good denitrification performance by the study of relationship between C/N ratio and denitrification efficiency. In this paper, unexpected total nitrogen average removal efficiencies is 38.9% because of unsteady carbon resource and small C/N ratio (average value 3.87). Because of no discharge of excess sludge, unceasingly accumulated phosphorus strength had a linear relationship with operation time. In this system, it is considerate that chemical phosphorus removal method should be used to intensify system phosphorus removal effect.As the research has shown, A/O-MBR has high remove efficiency and the quality of treated water is stabilized. It is a newly efficient process for the treatment of low-strength domestic wastewater.