Removal Of Nitrogen And Phosphorus From Biogas Slurry By Struvite Crystallization

With the improvement of agriculture, intensive livestock breeding industry develops in high-speed. However, this development likely results in the excessive concentration of livesrock wastewater, leading to utilize and process biogas slurry more difficultly. The application of struvite crystallization method to process biogas slurry, can not only effectively remove the nitrogen and phosphorus from biogas slurry, provide favorable conditions for subsequent biochemical treatment, but also achieve the effective recycling of nitrogen and phosphorus, favoring the sustainable development of biogas industry as well as nitrogen, phosphorus resources.Simulated wastewater and biogas slurry from cattle farm have been used to research the struvite crystallization method systematically. To explore the influencing factors and their changing rules, static experiments and dynamic experiments were performed, respectively, with the removal rate of phosphorus and ammonia nitrogen as response indicators. The results are indeed available to optimiz the parameters in struvite crystallization process and evaluate its removal ability of nitrogen and phosphorus from biogas slurry, providing a scientific basis for biogas slurry treatment process.The results from static experiment based on simulated wastewater indicate that, the pH hasing the greatest impact on phosphorus, ammonia removal efficiency is the most important factor constraining struvite crystallize. The optimum value of pH and Mg:P for the reaction is9.5and1.2:1, respectively. Little influence of reaction temperature and reaction time on the removal efficiency of phosphorus and ammonia was revealed, and the optimal temperature and time for the reaction is about25℃and5～10min. The results of dynamic experiment show that the struvite crystallization reactor has good treatment effect of phosphorus, ammonia nitrogen for the simulated wastewater in which the TP,TN concentrations were62mg/L and292mg/L, while the removal rate is maintained at80%and40%, respectively. To keep the effluent concentration of phosphorus below8mg/L, the water flow rate must be controlled at less than3.4L/h.The enhancement testing of low concentration of biogas slurry shows that the order of impact factor of the phosphorus and ammonia nitrogen removal rate is:pH, temperature, Mg:P, which coincide with the simulated wastewater test. The optimum value of pH and Mg:P is9.5and1.2:1, respectively. This reaction is able to obtain good treatment effect at room temperature. The treatment effect of low concentration biogas slurry is lower than simulated wastewater. For biogas slurry which TP, TN concentrations were33.5mg/L and259mg/L, the phosphorus, ammonia nitrogen removal rate is maintained at70%and35%, respectively. To control the phosphorus effluent concentration below8mg/L, the water flow rate must be less than4.34L/h.Struvite crystallization process of high concentration of biogas slurry from cattle farm expriment verify that pH is the most important factor restricting of the struvite reaction again, and the optimal pH and Mg:P is9.5and1.3:1. Additional phosphorus can effectively improve the removal rate of ammonia nitrogen in the biogas slurry, even to81.42%. When keeped P:NH4+at1:1, phosphorus and ammonia nitrogen removal rate rising with the increasing of Mg: NH4+, while the phosphorus concentration reduced from38.29mg/L to22.29mg/L, the removal rate of NH4+and P increace from47.21%to69.27%and36.85%to80.31%, respectively. The removal rate of struvite crystallization apparatus of phosphorus, ammonia nitrogen for high concentration biogas slurry, which TP, TN concentration were72.53mg/L and568mg/L is more than69%and22%, in the case of adjust the pH and add magnesium source. The optimal pH, Mg:P and influent flow rate is9.5,1.3:1and2L/h. At this point the effluent phosphorus concentration is20.25mg/L, phosphorus and nitrogen removal efficiency is72.07%and29.88%, respectively.