| Taking high efficient function mechanism of A-step in AB process as core, the content and component of extracellular polymer substances (EPS) in different state were studied by means of advanced extracting technology of EPS, and from the angle of EPS in activated sludge, these mechanisms of adsorption-regeneration, bio-flocculation and sedimentation performance of A-step in AB process were studied deep in this paper. Putting forward the new viewpoint that extracted EPS affected sludge bulking, its function mechanism was also probed. Firstly using extracted EPS to simulate forming of bio-flocs, the quantitative effect of EPS, Ca2+ and pH on bio-flocculation was studied, moreover the mode of synthetical effect was deduced. The adsorption-regeneration mechanism was perfected by testing the change of dehydrogenase and EPS in activated sludge. At one time, to settling the problem of excess sludge in A-step, the rule of bacterium multiplication and yield of sludge in A-step were studied. Besides, treatment of low-concentration wastewater and effect of low-concentration wastewater on microorganism in A-step were also involved in this paper. The main conclusions are as follows:1) The study on only using A-step to treat low concentration municipal wastewater(BOD5=100mg/L showed: When influent COD was 170~288 mg/L, BOD5 was 67~137mg/L, Ns was 0.5~3.0 kgBOD5/kgMLSS-d and HRT was 75~25min, the effluent COD was less than 60mg/L, effluent BOD5 was less than 20mg/L and effluent SS was less than 20mg/L. The cause of good treatment effect was that EPS content of sludge in A-step reactor was more (EPS=20.25~26.21mg/gVSS), which resulted in biggish absorption and flocculation capability of sludge; and with NS of reactor increasing, dehydrogenase content, activity and metabolizability ability of sludge also increased. No primary sedimentation tank, which made fresh wastewater and SS directly enter into A-step, improved sedimentation performance of activated sludge, and microbial supplement could be gamed from inflow, which maintained concentration of sludge; microorganism phase in reactor was very abundant and there were many sessile vorticella.2) The experiment results indicated that the inflow SS distinctly improved sedimentation performance of activated sludge; pythogenous wastewater evidently worsened sedimentation performance of activated sludge, and canceling primarysedimentation tank would avail to stable running of wastewater treatment plant. At one time, the orthogonal experiment showed: the effect of loading rate Ns on sedimentation performance of activated sludge was highly remarkable, meanwhile the effect of dissolved oxygen and wastewater temperature on that is less; moreover the synthetical modes of effect of loading rate Ns and dissolved oxygen or loading rate Ns and wastewater temperature on S VI were concluded:SVI = 84.74 - U.SNs + 3.33DO SVI = 64.02 - 5.52Ns + 2t- 0.39t3) The effect of EPS on sedimentation performance of activated sludge was studied by means of extracting EPS from activated sludge. The experiment indicated: the effect of loading rate Ns on EPS was highly remarkable, meanwhile the effect of dissolved oxygen and wastewater temperature on EPS was less; and EPS were correlated evidently with sedimentation performance of activated sludge; the correlative model was concluded:SVI=4.12EPS-21.658The effect of loading rate Ns on sedimentation performance of sludge resulted actually from the effect of loading rate Ns on EPS, which was apparent behavior of loading rate Ns on EPS. The synthetical modes of effect of loading rate Ns and dissolved oxygen or loading rate Ns and wastewater temperature on EPS were concluded by orthogonal experiments:EPS = 21.W -3.39Ns + 0.9DO EPS = 22.25 - 2.1 BNs + 0.2tThe experiment discovered the content of polysaccharide of EPS in low loading rate sludge was high, and the effect of polysaccharide on filament could be the important cause of sludge bulking in low loading rate.4) The quantitative effect of EPS, Ca2+ and pH on bio-flocculation was studie...
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