The Study On Pretreating Microcystins In Micro-polluted Source Water By Biological Aerated Filter

In recent years,water eutrophication degree intensifies day by day because of environmental pollution.Cyanobacteria bloom outbreaks frequently and its main harm is to release many different algae toxins into water. Microcystin(MC) is the most occurence and harmful algae toxins. High incidence of carcinoma has positive correlation with these toxins and it directly threats human health. So control of algae toxins are necessary.Conventional feed water treatment processes such as coagulation, sedimentation and filtration can not completely remove microcystins in water.So conventional processes augmentation is a strategy to control algae toxins. Secondly, deep purification can effectively remove algae toxins.But cyanobacteria bloom pollution has certain stage and abruptness character. Therefore, the most safe and effective strategy is to eliminate microcystins in the water through the source water pretreatment process, so that it does not enter the follow-up water treatment systems.Currently, study at home and abroad for MCs was concentrated on isolation of MCs degrading bacterium. How to use in process operation with MCs degrading bacterium has not been reported. Bacterium are engineered in biological aerated filter based on isolation of MCs degrading bacterium in this topic. Rapid adsorption and degradation of MCs are realized and new technology of the source water pretreatment is presented. Microcystins are eliminated in the water through the source water pretreatment process so that protecting drinking water safety. Through researches,obtaining the following main conclusions and outcomes:(1)Through classical bacteria isolation method, degrading bacterium DHU-28 and DHU-38 of MCLR and MCRR were obtained with MC-LR and MCRR as sole carbon and nitrogen sources and the surface waters in Dian shan hu,Shanghai as strain origin. Based on strain's morphology, physiology and phylogenetic analysis of 16S rDNA sequence, Strain DHU-28 was identified to be closely related to Stenotrophomonas (GenBank accession number is HM047512) and Strain DHU-38 was identified to be closely related to Pseudomonas fluorescens (GenBank accession number is HM047515).(2) Under the condition of 19.1-28.6℃,pH 7.23-7.46, gas-water ratio 1.5:1and hydraulic retention time 2.6h, flow rate and hydraulic loading of the ceramic BAF were respectively 0.35L/h and 0.28m3/(m2.h) and flow rate and hydraulic loading of high-performance fiber ball BAF were respectively 0.43L/h and 0.34m3/(m2.h). With the growth of HRT and the increase of gas-water ratio,removal rates of MCLR and MCRR have increased. The average removal rates of MCLR and MCRR were respectively 50.9% and 59% in the ceramic BAF. Removal rates of MCLR and MCRR were respectively 54.6% and 62.6% in high-performance fiber ball BAF.(3) The removal of MCLR and MCRR mainly occurred in the location of 60cm in BAF. During the location, the average removal rates of MCLR and MCRR were respectively 48.3% and 62.5% accounted for 85.6% and 92.5% of total removal rate. Growth rate became flat after the location of 60cm in BAF.(4) The average removal rates of MCLR and MCRR were respectively 50% and 60% in BAF inoculated engineering bacteria. The average removal rates of MCLR and MCRR were about 15% in BAF. It closed to the removal effect of empty bed filter layer.Adsorption properties of MCLR and MCRR in BAF showed that removal of MCLR and MCRR mainly related to adding of engineering bacteria.Through metabolism of engineering bacteria,MCs were degraded. Removal of MCLR and MCRR in BAF noninoculated engineering bacteria mainly depend on adsorption properties of filter.