| Struvite precipitation can simultaneously recycle two elements of nitrogen and phosphorus in sewage, and itself is an effective slow-release compound fertilizer, therefore, this technology attracts universal attention in recent years. The thesis is mainly based on municipal sewage quality situation of Three Gorges Reservoir area on the Yangtze River, incorporating with by-pass sludge reduction technology, about using struvite crystallization method remove and recycle nitrogen and phosphorus in sewage. This experimental research included two parts: on one hand, according to municipal sewage quality features of Three Gorges Reservoir area on the Yangtze River preparing nitrogen and phosphorus sewage, implemented single-factor beaker test, which mainly discussed pH value of reaction system; molar ratio of three ions to form the crystal; the influence of factors like reaction time and intensity etc. to the struvite formation and nitrogen and phosphorus removal effect. On the other hand, took the sewage in by-pass sludge reduction technology model anaerobic tank as raw water, then set up and experimented as per optimum parameter of the beaker test.Experiment result shows: in certain condition of temperature, reaction time and stirring intensity, when PO 34? initial concentration is low, pH value adjusting to 10.0 more or less, there is crystal formation, and the reaction is slow. Change of pH value before and after reaction to a certain degree reflects the reaction degree. The bigger the change is, the more thoroughly the reaction is. When pH value adjusts to about 9.0, the struvite formed is prismatic crystal; when pH value is over 10.5, the struvite formed is small, even lumped. We can see from X-ray spectrum, while pH value is around 9.5, formation substance has significant crystal characteristics. Meanwhile, water sample with PO 34? initial concentration of 1mmol/L(31mg/L), whose pH value is in the range of 10.0 to 10.5, or c(Mg 2 +): c(NH4+ ): c(PO 34? ) is 1:1:1, either can reach about 50%. If c(Mg 2 +): c(NH 4+ ): c(PO 34? ) is 1.5:1.6:1, struvite removing phosphorus effect is the best. PO4 3? removal ratio is about 55%, and ammonia-nitrogen removal ratio can reach 37%;water sample with PO 34? initial concentration of 2mmol/L(62mg/L), whose c(Mg 2 +): c(NH4+ ): c(PO 34? ) is 1:1:1, pH value 9.5 is the best, Max phosphorus removal ratio can reach as high as 75%,nitrogen removal ratio can reach 85%. If c(Mg 2 +): c(NH+4 ): c(PO 34? ) is 1.5:2.0:1, struvite P and N Removals effect is the best PO4 3? removal ratio is about 80% ammonia-nitrogen removal ratio is about 48%. Otherwise, neither reaction time nor stirring intensity influence to struvite P and N Removals effect is obvious. While choosing optimum value of these two parameters we shall consider struvite formation shape and nature precipitation recycling. Thesis considers the optimum reaction time is 25min,precipitation time is 60min,optimum stirring speed is 200r/min。By-pass sludge reduction technology model's anaerobic tank water experiment express that NH +4 removal ratio is 48.5%, which is higher than NH 4+ removal ratio of the prepared water in the same condition. The reason may be semi real sewage was adopted, whose water environment was complex, though testing sewage was supernatant, there still would left some other substance, like nitrifying bacteria etc. changing NH 4+ to NO 3?,NO 2? or other substance which including nitrogen. PO 34? removal ratio was 75%, basically conformed to the result prepared water experiment in the same conditions. The mentioned experiment result tells using struvite crystallization method remove nitrogen and phosphorus content in anaerobic tank supernatant is feasible.At last, the thesis analysis and evaluate the technology of struvite precipitation method recycling nitrogen and phosphorus in the aspects of social, environmental and economic. And find out struvite precipitation method has excellent development prospects and practical value.
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