Regulation And Control For Enhancing The Efficiency Of An A~2/O System Treating Cold Wastewater

In view of the actual situation of serious water pollution in Songhuajiang River Basin and low efficiency of sewage treatment facilities, through studying the regulating strategy of low-temperature A²/O system, the project proposed the idea that an anaerobic phosphorus release tank should be added after the secondary clarifier. Stimulated by the anaerobic conditions, it hoped to strengthen the sludge anaerobic phosphorus release, while increasing the aerobic metabolic activity of microbes, in order to comprehensively improve the treatment efficiency of A²/O system. An A²/O system treating cold wastewater was trial-produced and constructed, and the strategy and method of enhancing its treatment efficiency was studied by regulate and control operation .The result of treating cold wastewater at 14±1℃shows that A²/O system possesses significant COD removal efficiency, but the efficiency of nitrogen and phosphorus removal is so bad that the system need optimal controll. Firstly, without considering phosphorus removal, nitrogen phosphorus removal efficiency of the system was optimized. Under the condition that the sludge return ratio of the mid-sedimentation tank is 75% and the nitrification liquid recycle ratio is 100%, the low-temperature A²/O system that achieved better nitrogen removal and the concentions of effluent NH₄⁺,TN were 13.40 mg/L,28.23 mg/L respectively and their average removal rates were 74.61%,55.35% respectively.In order to improve phosphorus removal efficiency of low-temperature A²/O system, an anaerobic phosphorus release task was added after the secondary settling tank. On the basis of acquiring suitable operating parameters of anaerobic phosphorus release task through a static test, the phosphorus removal efficiency of A²/O system in different reflux sludge ratioes of the anaerobic phosphorus release task was investigated. The result indicates that the appropriate suitable operating parameters of anaerobic phosphorus release tank were that sludge loading between 0.015⁰.02 gCOD/gMLSS, NO₃^-concentration less than 5 mg/L, SRT for the 12 h, with slow stirring. The improvement of sludge recycle ratio of anaerobic phosphorus release effectively enhanced the simultaneous nitrogen and phosphorus removal. At the recycle ratio of 75%, the concentions of effluent COD,NH₄⁺,TN,TP were 30 mg/L,5 mg/L,15 mg/L,0.5 mg/L respectively.The analysis of sluge characteristics of A²/O system shows that the removal efficiency significantly decreased when MLSS reduced. Observed by scanning electron microscopy, the dominant microflora in anaerobic, anoxic and aerobic stage are brevibacterium, bacillus, and monococcus and the sludge bulking in aerobic stage was mainly caused by large population of filamentous bacteria, accompanied by high viscosity sludge bulking. Adopting measures of improving DO and organic loading and increasing emission amount of sluge, the sludge bulking was controlled efficiently after 35 d.