| With the rapid development of livestock and poultry breeding to intensive and large-scale and the wide range use of biogas project,the amount of biogas slurry produced far exceeds the amount that can be absorbed by local agriculture,and a large amount of biogas slurry is still being discharged into the environment.However,the biogas slurry contains a lot of nitrogen and phosphorus.Excessive nitrogen and phosphorus will cause eutrophication of the water body on the one hand,and phosphorus is a precious resource on the other hand,and random discharge will cause waste of resources.The struvite crystallization method(MAP)can simultaneously recover nitrogen and phosphorus in the biogas slurry,and can produce a high-quality slow-release fertilizer,but the ammonia nitrogen content in the biogas slurry is generally much greater than the phosphorus content,and a large amount of reagents need to be added during the recovery process.At present,there are few researches on alternative sources of phosphorus reagents.In this paper,phosphorus-rich wastewater is used as an alternative source of phosphorus and mixed with biogas slurry,through single factor experiment,Plackett-Burman experiment design and Box-Behnken experiment,the influence of struvite crystallization method with phosphorus-rich wastewater as the phosphorus source on the recovery of nitrogen and phosphorus in the biogas slurry was studied.The research results can provide an alternative options or theoretical reference for the treatment of biogas slurry and phosphorus-rich wastewater.The main research results are as follows:(1)In the single-factor experiment,it was determined that the best reaction conditions for the recovery of ammonia nitrogen and phosphate were: P/N=1:1,p H=9.5,Mg/N=1.2:1,stirring speed=200r/min,reaction time=15min and reaction temperature=25°C,the minimum residual ammonia nitrogen concentration is 20.47mg/L,the maximum ammonia nitrogen recovery rate can reach 97.08%,the minimum residual phosphorus concentration is 8.55mg/L,and the phosphate recovery rate can reach 99.44%.(2)In the intensive experimental research,the significant influencing factors screened by Plackett-Burman test were P/N,p H and Mg/N.The analysis of response surface experiment results showed that the order of the three significant influencing factors on ammonia nitrogen recovery rate is P/N>Mg/N>p H,and the order of phosphate recovery rate is P/N>p H>Mg/N.The optimized combination of reaction conditions is: P/N=1.03:1,p H=9.38 and Mg/N=1.2:1.Under these conditions,the predicted values of ammonia nitrogen and phosphate recovery are97.91% and 99.48%,respectively.The accuracy and reliability of the model were verified through 4 parallel experiments.The maximum relative deviation of ammonia nitrogen recovery rate was 2.46%,and the maximum relative deviation of phosphate was 0.38%,indicating that the relative deviation between the experimental value and the predicted value was small.(3)XRD diffraction analysis and SEM analysis showed that the precipitated product obtained under the optimal conditions contained struvite crystals.After purification,the struvite content in the precipitated product increased from 34.24% to 57.34%.(4)Under the experimental conditions,one ton of biogas slurry can be processed to obtain a benefit of 19.22 yuan.In the actual treatment project,for a project with an annual output of504 tons of biogas slurry,the net present value obtained after three years of operation is23501.15 yuan,which has a good economy.benefit.Moreover,not only can the phosphorus resources be recycled,but also the shortage of phosphorus resources can be alleviated,so it also has certain environmental and social benefits. |
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