| Basing on principle of nitrogen and phosphorus removal, related mechanism, process, research and development for domestic wastewater treatment both at home and abroad are presented in this paper. Also device and operating process of T oxidation ditch are studied and described, as well as its effect of nitrogen and phosphorus removal and controlling technique of operational parameter.Further more, this research takes T oxidation ditch for productive purpose in Changshu Northern Wastewater Treatment Plant as tester, in which the rules of organic matter degradation, DO distribution and main operational parameters are studied. Impact of organic matter concentration, DO level, volume loading ratio, HRT and SRT on nitrogen and phosphorus removal are analyzed respectively to conclude that when COD/TN is 3.7 and COD/TP is 34, nitrogen and phosphorus can be removed well as organic matter degraded effectively. T oxidation ditch of neither six or eight phases separated by rotor-brush can provide anaerobic, anoxic and aerobic conditions with proper distribution of DO which meet needs of phosphorus-accumulating bacteria, nitrobacteria (nitrosobacteria) and denitrobacteria. All the results show that as a secondary biological treating process of high efficiency of nitrogen and phosphorus removal, T oxidation ditch can be applied well to domestic wastewater treatment in our country.Contrasting theoretical analysis with practical operational parameter, we suggest appropriate parameter range and controlling process of T oxidation ditch should be that BOD-sludge loading 0.055kgBOD5/(kgMLSS d), SRT 15~20d, volume of settling zone accounts 1/4 of total tankage, and surface loading of relevant settling zone 0.196 m3/m2·h.Our research findings will make great sense to lead practical device and operating management of T oxidation ditch as a secondary intensifying process for domestic wastewater treatment.
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