Source Control Technology Of Nitrogen And Phosphorus Pollution In Domestic Wastewater Based On Crystallization Reaction

The situation of water environment pollution and the phosphorus resources shortage has become one of the bottlenecks that restrict the sustainable development of social economy seriously in our country,and an important strategy to solve this problem is to make use of the sewage resources.In addition,how to control the source pollution of nitrogen,phosphorus and other nutrients recovery is a topic of general interest now.Magnesium ammonium phosphate crystallization is a kind of hot technology which can not only remove phosphorus,but also recover phosphorus resources.And compared with other methods,this method reduces the cost of treating excess sludge,and the product of magnesium ammonium phosphate crystal can be used as fertilizer,feed additive,coating and raw material for producing phosphate rock.And it can produce certain economic benefits.Based on this,the subject took pretreatment reactor,steel slag-based crystal seed filter and fluidized bed crystallization reactor as the support and simulated and actual septic tank wastewater as experimental water samples.Through the investigation of typical city septic tank wastewater quantity and quality,the study analyzed the dynamic characteristics of magnesium ammonium phosphate crystallization based on typical septic tank wastewater,discussed the influence factors of magnesium ammonium phosphate crystallization of typical septic tank wastewater.The preferred pretreatment process was selected,then the effects of magnesium ammonium phosphate crystallization of septic tank wastewater by steel slag seed crystal filter and fluidized bed crystallizer was studyed,and the reactor of hydrolysis pretreatment combined with fluidized bed crystallization was structured,to provide reference for researching new septic tanks waste water sources pollution control and resource utilization technology.The results showed that the septic tank wastewater had the characteristics of typical functional areas,and the overall trend of septic tank wastewater of each season was consistent,which concentrations in summer were slightly higher than that in other seasons.The water quality analysis showed that the septic tank wastewater was a typical high ammonia and low phosphorus wastewater.Based on this,through adding magnesium source,adjusting the pH value and other factors,MAP crystallization reaction test was occurred.The result showed that the concentration of nitrogen and phosphorus were decreased,and the average removal rate of 9.9%and 75.5%,respectively.The characterization of SEM and EDS to crystalline product showed that the precipitate was MAP,and the crystal shape of uniform,but arranged disorderly,and the effect of becoming crystal is poor,which declared septic tank wastewater by MAP crystallization removal and recovery of nitrogen and phosphorus resources has the realistic feasibility.The basic characteristics of typical septic tank wastewater MAP crystallization were studied.The results showed that the process was in accordance with the two-stage reaction kinetics,namely 1/[PO₄^3--P]and time was proportional to the reaction into the model for y=1/（0.00533x+0.06803）（x and y represented time and phosphorus removal rate respectively）.R² of equation model and the data was 99.72%,and the calculated reaction rate constant is 6.012×10^-3.Based on this,the study investigated the effect law of pH value,ammonia concentration,reaction time,aging time and Mg/P ratio to MAP crystallization reaction for simulated septic tank wastewater and analyzed the main factors of effecting septic tank wastewater reaction rate by crystallization of MAP was pH value,ammonia concentration and Mg/P ratio.Through the response of surface analysis,the results showed that the optimal conditions were that pH value 9.63,Mg/P ratio 1.37 and ammonia nitrogen concentration 115.3mg/L.The model of phosphate removal rate of BBD test was Y=-92.45+18.31A+27.66B+0.27C+2.42AB+0.024AC-0.060BC-0.94A²+5.89B²+5.893E-004C²（A,B and C represented the pH value,Mg/P ratio and ammonia concentration,respectively）.In the meantime,through the internal residual model of normal probability and actual value and predictive value of removal rate,which can be obtained that the model explained the relationship between the removal rate and pH value,Mg/P ratio and initial ammonia concentration admirably.Based on the quality of typical septic tank wastewater and the key influencing factors,the test investigated the effect of pretreatment technology such as hydrolysis,coagulation and ceramic membrane to pH value,SS,COD,ammonia nitrogen and phosphorus,and determined the hydrolysis process served as the pretreatment technology of septic tank wastewater.The three key factors affecting steel slag crystal filter were inspected,determining the optimum pH value was 9,HRT was 90min,Mg/P was 1.2:1.According to the optimization conditions,the steel slag crystal filter runed 30d.Under the conditions of influent ammonia nitrogen and phosphorus concentration is relatively stable,the treatment effect of reactor was better,the stable removal rate reached 80%.Through air water backwashing,obtained crystallization product was characterized by XRD,which showed that the crystal was magnesium ammonium phosphate,and it had high recovery value,Similarly.The two key factors affecting fluidized bed crystallizer were inspected and HRT was 60min,the optimum pH value was 9.5.The fluidized bed crystallizer worked 8d,COD,ammonia nitrogen and phosphorus removal efficiency were higher in stable operation,and reached 43.6%,41.3%,91.2%respectively.The concentration of phosphorus of wastewater was relatively low,basically maintained at about 2mg/L.Through the investigation of VFAs production,pH value,nitrogen and phosphorus content and biodegradability,the start-up time of hydrolysis reactor was40d.The way of adjusting the proportion of nutrient solution and septic tank wastewater can be effectively shortened start-up time of reactor.Using hydrolysis pretreatment combined with fluidized bed crystallization treatment reactor treated simulated septic tank wastewater,the process characteristics of combination technology was investigated,and the optimal operating conditions were determined.Under this condition,the combined reactor treated actual septic tank wastewater of the living area and office area respectively.The results showed that the pollutant index of office area was fluctuated larger,the treatment capacity of reactor was unstable because of small concentration of nonworkdays.The average ammonia removal rate of septic tank wastewater in living area was 46.8%,while the highest phosphorus removal rate reached 93.1%,Which indicated the combination process had outstanding treatment effect on actual septic tank wastewater and this technology can be used as a selected process of city sewage nitrogen and phosphorus pollution control and resource recovery.