Study On Effect Of Extracellular Polymer Substances And Their Surface Properties On The Flocculation And Settlement Of Activated Sludge

Solid-liuid seperation is key problem in running of activated sludge system,which influnces the quality of effluent and the concentration of returned sludge.Extracellular Polymeric Substances (EPS) is important part of activated sludge, which locates in interior and outerior, and has improtant effect to flocculation and settlement of activated sludge. However, the exactly influence of EPS to flocculation and settlement is not clear.In the past research, only from the total amount and components of EPS and the surface properties of floc, the effect of EPS to flocculation and settlement of activated sludge was study, but not from the surface characters of EPS. Furthermore, mostly researcher took the EPS as a whole, ignoring the difference between interior EPS and outerior EPS. In the dissertation, taking the activated sludge in test scale system as the object, loosely bound EPS and tightly bound EPS were extracted by ultrasound and cation exchange resin. Not only the change of components,amounts and surface properties of LEPS and TEPS, but the effect of two type EPS and their surface to flocculation and settlement were studied. The main conclusions of the study were as follows:1) For the flocs of different SRT systems, protein was the main components of LEPS and TEPS, carbonhydrate and humic substance were next, and the amonunt of DNA was small. The amount of LEPS changed greatly with the change of SRT(3d to 15d),which was 25.6~62.7mg/g VSS, while that of LEPS changed little,which was 80.6~84.4mg/g VSS. While the SRT increased from 3d to 20d, the value of surface charge of LEPS decreased early, then increased little latterly, which was -1.59~-0.77meq/g EPS.When SRT was 15d, LEPS have lowest value of surface charge and highest hydrophobicity. By the contrast, the value of surface charge of LEPS changed little with the increase of SRT (3d to 15d), which was -1.26~-0.98meq/g EPS. Furthermore, tightly bound EPS was more hydrophobic than loosely bound EPS.2) After LEPS and TEPS was extracted by ultrasound and cation exchange resin, some EPS still remained in the residual sludge.beacause Zeta potention of residual sludge was about -32mv, the resuspended mixed liquid was steady.3) Surface charge of activated sludge was effected by the amount and surface charge of LEPS affected than those of TEPS. The increase of amount and surface charge of LEPS led the increase of surface charge of sludge.The hydrophobicity of sludge were more significantly related to the hydrophobicity of TEPS than that of LEPS, but less to the amount of TEPS.4) The amount and surface properties of LEPS affected flocculation of activated sludge more than those of TEPS. The increase of amount and surface charge value of LEPS would increase ESS, but those of TEPS had less effects to flocculation characters of activated sludge.Furthermore, higher hydrophobicity of two type EPS was corresponded to lower ESS and higher FA.5) While the total amount and surface charge value of LEPS increased or their and hydrophobicity dropped, SVI would be enhanced and ZSV would be reduced. The total amount of TEPS was not significantly related to SVI and ZSV, while hydrophobicity of TEPS had strong effects to SVI and ZSV. That is to say, higher hydrophobicity of TEPS was corresponded to lower SVI and higher ZSV.