Study On The Advanced Treatment Of Municipal Sewage By MF/UF

Since the water scarceness is worsening and the municipal sewage as thealternative resources has become a common understanding, the recycling of themunicipal sewage has drawn more and more attention throughout the world. Againstthis background, this paper tries to discuss the advanced treatment of the municipalsewage treated through biochemical methods with the aim to reuse it.After the sewage analysis and a comparison with the quality standard of reusewater, it is clear about which contamination in the municipal sewage still needscleaning. In the study, the microfiltration (MF) and ultrafiltration(UF) technology isadopted to treat the sewage. The pilot scale device is employed.The membrane performances of MF and UF are tested in the experiment andappropriate operation modes are explored.Sand-filter as a pretreatment method can effectively remove part of the organicsand the rejection of CODcr is about 25.8%. The following experimental results showthat the CODcr of MF product water is below 30mg/L, the total amount of bacilli isabout 600cfu/mL on average, and the product turbidity is below 2NTU. The quality ofMF product water is steady and will be better than that of the reuse standard afterfurther disinfecting.The quality of the MF product water does not vary under different operationconditions, but is greatly affected by the quality of feed water. As the operatingpressure increases, the product water flux rises. However, under too high operatingpressure, the product water flux shows a remarkable drop. The worsening of feedquality could cause irreversible pollution, which leads to the drop of product waterflux. The increase of the feed velocity can help to increase the product water flux.After a long-term run, the membrane was seriously fouled and its performanceaccordingly falls on the whole. Here a mode (production: 40 minutes;backwash: 3minutes) is proposed to maintain the membrane performance of rejection andpermeability. Chemical washing can achieve good results when alkali washing,NaClO washing and acid washing would be combined together.The UF experiment shows that the CODcr of product water is below 25mg/L, thetotal amount of bacilli is 430cfu/mL on average, and the turbidity is below 0.6NTU.The water's quality will be better than that of the quality standard of reuse water afterfurther disinfecting. The product of UF is better than that of MF, and it has littlefluctuation with the variation of feed water quality. The operating pressure and thefeed velocity have the same impact on UF as MF. Besides, the UF can maintain adesirable performance in a long-term run. Through a washing mode (production: 45minutes;backwash 1 minute), the UF membrane performance can be restored to ahigher degree. The combination of NaClO washing and alkali washing will achievegood washing effects.