Effect Of Organic Matter In The Micro-polluted Source Water On Operation Of Slow Sand Filter

At present,part of the drinking water are severely contaminated,the conventional water treatment technology can not completely get rid of the pollutants in the micro-polluted source water.The slow sand filter has the advantages of physical interception and biological action,and has the advantages of good treatment effect and low cost..In micro-polluted source water,the organic matter mainly occurs in form of dissolved organic matter and organic matter with particle size larger than 450 nm.,the difference of organic matter will lead to the difference of the characteristics of schmutzdecke.However,there are few studies on the characteristics of the schmutzdecke and the removal of pollutants in the slow sand filter.In this study,two slow filtration systems for simulating organic pollutants in micro-polluted source water with humic acid and glucose were established.The effects of different organic forms on turbidity,ammonia nitrogen,nitrate nitrogen and organic matter removal were discussed,the particle size and morphological structure of the schmutzdecke material are analyzed and observed,the extracellular polymeric substance(EPS)of schmutzdecke material is extracted by the method of heat extraction,and the bacterial community structure in the schmutzdecke were sequenced using Illumina platform.The differences of EPS components and contents and microbial phases in different systems were identified,and the reasons for their difference in removal efficiency were also revealed.The research results mainly include several points:(1)In the SSF system with humic acid as an organic substrate(SSFP),microbes growed on the humic acid particles,and the particle size of schmutzdecke material was smaller and the structure of schmutzdecke material was looser,which ensured the stability of the SSF.In the SSF system with glucose as the organic substrate(SSFD),there were a large number of microbial flocs wrapped in filamentous bacteria in schmutzdecke,the particle size of schmutzdecke material was larger and the structure was tighter,which easily led to the blockage of SSF.(2)The hydrolysis of humic acid in the SSFP system restricted the growth of heterotrophic bacteria,which may also provided more favorable survival conditions for the autotrophic bacteria,which makes the system had better nitrification.In SSFP,the removal rate of ammonia nitrogen could reach 90%,however,In SSFD,the activity of heterotrophic bacteria was stronger,which maked the removal rate of ammonia nitrogen was only about 24%.(3)In the SSFP,the average removal rate of total organic carbon(TOC)is 22.68%,and the maximum removal rate of TOC could reach 45.45% with the increase of operating time and temperature.So,the increase of temperature is beneficial to microorganism using humic acid organic matter,but in the SSF which was stable,the elevated temperature had no obvious effect on nitrification.(4)The hydrolysis of humic acid in SSFP increases the total amount of the extracellular polymer(EPS)and the content of the protein in the soluble EPS.(5)The small molecular substance(glucose)in the influent,which is easy to be used by microorganisms,could make the diversity of microbes higher.(6)The increase of the organic particles in the influent is beneficial to the attachment and growth of nitrifying bacteria and the ratio of the Nitrosomona in SSFP reached 37.68%.And,we found that the most significant difference among the two systems is Nitrosomona,which may also be an important reason for the difference of nitrification performance between the two systems.