| The history, recent situation and trend of urban sewage treatment all over the world was described in this paper. It debated that high constructing fund and higher running expenses are presently influencing the development of urban sewage treatment in China. For ubiquitous unstable-running and higher use on energy in operating period of existing urban sewage treatment plant, the author made Shijiazhuang City Wastewater Treatment Plant (SJZWWTP) as an object of research and studied on optimal controlling for aeration by experiments and site practice. The relatives among DO, MLSS (Mixture Liquid Suspended Solid), disposing effect, activated sludge's characters, microbes has been revealed. The controlling conditions for sustainable running of urban sewage treatment plant have been regulated. The results are as follows::(1) The aeration is the main controlling object of sustainable running in wastewater treatment process with fine pore diffuser. The optimum operation situations of SJZWWTP are: MLSS=1.5 ~ 2.0g/L, ML VSS/MLS S=0.62 ~ 0.66 ( Fw=0.2 ~ 0.4 kgBODj/kgMLVSS.d) , DO=1.0~ 1.5mgO2/L; Returning ratio =100%.(2) Under low loading in aeration, when DO<1.0mgO2/L, the situation is in anoxic environment, the concentration of MLSS is lower, both the activity and flocculating-setting character of activated sludge are worse, the number of microbe is small, the disposing ratio is lower; when 1.0mgO2/L DO 1.5mgO2/L, the supply of oxygen is satisfied, the concentration of MLSS is the highest, both the activity and flocculating-setting character of activated sludge are the best, the number of dominant microbe is suitable, the disposing ratio is the highest; when 1.5mgO2/L DO 3.0mgO2/L, the phenomenon of peroxidation is increasingly appearing, concentration of MLSS gradually becomes lower, both the activity and flocculating-setting character of activated sludge increasingly become worse, the number of microbe gradually decreases, the disposing ratio becomes lower.
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