The Study On Removal Of Organic Pollutants From Urban Runoff Rainwater By Activated Sludge Process

In recent years,sponge city,as a new concept of urban construction,has gradually entered the public eye,and rainwater utilization has become a new exploration field.Under the premise of ensuring urban drainage and waterlogging prevention,rainwater storage--infiltration--purification process in the city can be reasonably realized,which is conducive to ecological protection and rational utilization of resources.However,there is a great difference between the composition of rainwater and the content of organic matter in different areas.In order to solve the problem of water quality corruption during rainwater storage,the research group tried to use activated sludge to quickly remove COD and ammonia nitrogen in rainwater,and explored the dynamic parameters and performance indexes of activated sludge suitable for rainwater treatment.Compared with ordinary domestic sewage,the lack of metal ions is the main feature of rainwater quality.Therefore,the improvement of activated sludge dehydration performance after adding calcium,magnesium,iron and other metal ions in rainwater was also discussed during the study.Sequential batch bioreactor(SBR)is used,the main research indicators are: sludge volume index(SVI),mixed liquid suspended solids concentration(MLSS),mixed liquid volatile suspended solids concentration(MLVSS),COD removal rate,ammonia nitrogen removal Rate,sludge yield coefficient,sludge ? value(the ratio of MLVSS to MLSS),capillary absorption time(CST)and microbial community characteristics.At the same time,the activated sludge method was used to treat the simulated wastewater from toilet flushing,and the difference between the treatment effect and the sludge characteristics of the wastewater from tap water flushing was observed and analyzed;In activated sludge quickly remove pure water COD and ammonia nitrogen experiment,by changing the parameters of dynamics-organic sludge domesticated activated sludge load and get the optimum parameters of the load and sludge ? value,namely when the ? value is0.7,sludge load is 0.3 kgCOD/kgMLSS·d,COD removal rate reached 96.4%,ammonia nitrogen removal rate was 52.8%,the lowest water COD can be up to 8.0 mg/L,ammonia nitrogen is 6.0 mg/L.Compared with other load parameters,the biomass in the activated sludge under this load is larger,and it can adapt to the rainwater load with short reaction time,which can quickly remove the organic pollutants in the rainwater.The effluent quality meets the requirements of "municipal wastewater recycling and municipal miscellaneous water quality"(GB/ t18920-2002).In order to improve the activity of sludge dewatering performance indicators CST(Capillary Sucion Time Capillary suction Time),enhance its settlement performance,in the rain to join the right amount of calcium,magnesium,iron metal ion,shorten the CST values,the following order: CST rain > CST magnesium> CST calcium ions > CST iron ion,namely compared to iron,ions can significantly shorten the sludge Capillary suction Time,improve sludge settling performance.From the above results,itcan be seen that the activated sludge process can effectively remove the organic pollutants in rainwater in a short reaction time,reduce the ammonia nitrogen content,improve the dehydration sedimentation performance of sludge by adding metal elements,and reduce the burden of sludge disposal.The results of simulated rainwater flushing wastewater treatment by activated sludge method showed that the apparent yield coefficient of activated sludge in the tap water flushing reactor ranged from 0.67 to 0.92kgMLVSS/kgCOD,and that of the rainwater flushing reactor ranged from 0.52 to 0.71kgMLVSS/kgCOD.The SVI value in the rainwater flushing reactor remained at about 82mL/g,and that of the tap water at about 76mL/g.Microscopic examination revealed the presence of a large number of meiozoan and mature bacterial micelles,indicating that the activated sludge acculturated by rainwater flushing wastewater had similar sludge sedimentation and flocculation properties as that of tap water,and was not prone to sludge swelling.Two different types of flushing wastewater can achieve a high COD removal rate,maintained at about 84%;The COD concentration of the effluent can reach80mg/L,reaching the level 2 discharge standard of urban sewage treatment plant pollutant discharge standard(GB18918-2002).To sum up,from the perspective of pollutant removal capacity and sludge performance indexes,the capacity of flushing rainwater reactor is similar to that of tap water reactor.Using rainwater as a new source of flushing water to replace tap water will not affect the stable operation of sewage treatment facilities in the later stage.By Illumina Miseq sequencing technology,the four kinds of rain water activated sludge samples(pure rain-the R20,adding the calcium ion-CA20,adding the magnesium ion-MG20,cast iron ion-FE20)and a tap water activated sludge control samples-W20 microbial population structure and function of gene prediction analysis,the results showed that the rain activated sludge samples Alpha diversity increases,adding the calcium and magnesium ions can increase the number of microbial populations(OTU)about 5% ~ 8%;The OTU Venn diagram shows that the similarity of the four types of stormwater based activated sludge sample populations(OTU)reaches about 50%,while that of the ordinary activated sludge sample population is less OTU and its diversity is low.The analysis of the horizontal community structure of phylum,class,order,family and genus showed that Planctomycetes accounted for more than 60% in R20 of rainwater activated sludge samples,and was the maximum abundance value in each sample,corresponding to the dominant fungi.The dominant species in each sample of rainwater base were Planctomycetacia ?Pirellulales,Planctomycetales ? Pirellulaceae,Gemmataceae ? Pirellula,Gemmata.Calcium,magnesium and iron ions can promote the increase of Proteobacteria ?Gammaproteobacteria and Verrucomicrobia ? Verrucomicrobiae ?Verrucomicrobiales.The results showed that the fungicularia microorganisms could adapt to the rainwater quality and develop into a dominant population,which indicated that themicrobial community of the activated sludge cultivated and acclimated by rainwater had an adaptive change,which was suitable for the degradation of aliphatic hydrocarbons,polycyclic aromatic hydrocarbons(PAH)and other organic compounds from the processes of coal and oil combustion and plant emission in rainwater.The addition of calcium,magnesium and iron metal ions promoted the increase of the abundance of many populations in proteobacteria and Verrucomicrobia of verruca.Sample functional genes Metabolism secondary gene prediction analysis showed that,Lipid Metabolism and Xenobiotics Biodegradation and Metabolism genes in four rain water activated sludge samples average abundance than the control group,difference value were 0.42% and 0.35% respectively,with significant and should be related to proteobacteria as the dominant fungi.