Study On Nitrogen Ammonia And Phosphous Removial From Biogas Slurry By Struvite Crystallization

The higher content of ammonia nitrogen and phosphorus in biogas slurry of pig farm is one of the main causes of eutrophication and red tide in nearby water bodies if the swine waste water is discharged without treatments. The seek of economic and efficient processing technology of biogas slurry is the key to solve environment problem caused by the emission of biogas slurry. As a new waste water treatment technology, struvite precipitation(magnesium ammonium phosphate, the English abbreviation for MAP) is an effective process for the synchronous removal and recovery of ammonia nitrogen and phosphorus from biogas slurry. It is quite significant to realize cyclic utilization of ammonia nitrogen and phosphorus in swine waste water for slurry pollution control and resource recovery and utilization. In this thesis, the swine slurry is the research object and the ammonia nitrogen and phosphorus recovery efficiency is taken as the index. By small scale and pilot scale test, the optimum conditions of the struvite precipitation treatment of biogas slurry were obtained. The ingredients of the small scale and pilot scale test product were analyzed by XRD technology. In the meanwhile, the economic costs of this system were analyzed. The results were as follows:With swine biogas slurry, small scale batch experiments of struvite crystallization were carried out, adopting MgCl2·6H2O and Na2HPO4-12H2O as the recourse of magnesium and phosphorus. By single factor experiments, Plackett-Burman Design and Box-Benhken Design the study drew the conclusion that the pH value, the molar ratio of Mg/Ns P/N are the three main influence factors. The results showed that the optimism reaction conditions were pH value 8.7, Mg/N molar ration 1.3:1, P:N molar ration 1:1. For the nitrogen ammonia efficiency,the interaction effect of pH and Mg/N, and pH and P/N were extremely remarkable, the interaction effect of Mg/N and P/N was remarkable. For the removal efficiency of phosphous, the interaction effect of pH and Mg/N, Mg/N and P/N was remarkable,the interaction effect of pH and P/N were less remarkable.Under this condition, the removal efficiency of ammonia nitrogen and phosphorus respectively were 89.29% and 90.09%. The effects of reaction time, stirring speed and reaction temperature were not significant. Thus, in order to simplify the operation process and save the processing cost, the values of these three factors were respectively 10min、200r/min,25 ℃. The result showed that the measurements of ammonia nitrogen, phosphorus and magnesium were approximate to the theoretical value. The content of the small scale product were:ammonia nitrogen 5.6%, phosphorus 28.1%, magnesium 15.7%. Combine with the analysis of XRD, the small scale product were mainly composed of struvite.Considering the effects of different aeration rate on the removal efficiencies of ammonia nitrogen and phosphorus due to the design of the experiment device, the effects of the pH value, the molar ratio of Mg/N and P/N and the aeration rate were studied in this paper. For the nitrogen ammonia efficiency, the interaction effect of pH and Mg/N, pH and P/N, pH and aeration rate were remarkable; Mg/N and aeration rate,Mg/N and P/N, P/N and aeration rate was less remarkable. For the removal efficiency of phosphous, pH and Mg/N was remarkable,pH and P/N,pH and aeration rate,Mg/N and P/N, Mg/N and aeration rate,P/N and aeration rate were less remarkable.The results showed that the optimism reaction conditions were pH value 8.6, Mg/N molar ration 1.2:1,P/N molar ration 1:1 and aeration rate 90L/min. Under this condition, the removal efficiency of ammonia nitrogen and phosphorus respectively were 64.21% and 63.12%. And the pilot scale experiment product were:ammonia nitrogen 5.5%, phosphorus 28.3%, magnesium 15.5%. Combine with the analysis of XRD, the pilot scale product were mainly composed of struvite. The treatment cost of one ton swine biogas effluent was 24.95 yuan and the struvite profit of one ton sine biogas effluent was 28.05 yuan. Thus it can be seen that the struvite precipitation as a new method to simultaneously recover ammonia nitrogen and phosphorus satisfies the sustainable development idea of economy, society and environment.Choosing the biogas which was treated by MAP as the resource to treated the maize straw,the results showed that the crystallization was declined 10.76%.The analysisof XRD and SEM results showed that the structure was broken after treated by the biogas which was efficient to enhance the utilization of the maize straw.