Study On Nitrogen Recovery In Rural Refuse Leachate By The Process Of Magnesium Ammonium Phosphate Crystallization

A large amount of leachate was produced during the transportation and compression of domestic refuse.The high concentration of ammonia nitrogen and organic pollutants contained in leachate,restricted by the operation and maintenance conditions of rural refuse leachate disposal facilities,could not be treated effectively,which may cause serious threats to the surrounding water environment.Magnesium Ammonium Phosphate(MAP)crystallization was used to recover nitrogen from rural refuse leachate under lab-test and pilot-test.This paper took simulated water from lab and raw leachate from transfer station as the research object,explored the actions of p H value,molar ratio of ion in solution,stirring intensity and precipitation time on MAP crystallization reaction.The optimal conditions under the simultaneous multiple factors were obtained by central composite design.When p H=9.8,n(Mg):n(N)=1.19: 1,GT=190,000 and precipitation time =30 min,the optimal recovery rate of ammonia nitrogen in two effluent samples was 84.3% and80.8%,respectively.The recovery rate of ammonia nitrogen in the raw leachate increased with the initial load in a 20 L piloted reactor and could reach 71.5%-74.8%under both single-pass and sequence-batch operating mode.Furthermore,struvite(STR),mealworm fecal biochar(MFB)and corn stalk biochar(CSB)were used as crystallization seeds to investigate the effects of seed dosage,p H value,initial load and reaction time of ammonia nitrogen recovery.Among them,the recovery rate of ammonia nitrogen could reach 84.1%,83.7%,79.8% at 0.5 g/L of STR,MFB and CSB.Through the characterization analysis of products such as scanning electron microscopy,infrared spectroscopy,X-ray diffraction,this paper proved that the products generated by the crystallization reaction were consistent with the MAP standard atlas.The crystals synthesized in raw water had a larger particle size and a looser arrangement structure,which enriched more impurities on the surface of seed,so that had a certain removal effect on fluorescent substances and macromolecular organic matter in leachate.Through the ecotoxicity analysis such as organic matter screening,seed germination index,and survival rate of earthworm,the heavy metal content of the crystal was proved to be lower than the limit of agricultural fertilizer standards,which could pass the index system of security and would not cause harm to life.The experimental conclusions provided theoretical support for exploring the design parameters and recovery efficiency of the mobile vehicle leachate disposal facility.However,the removal efficiency of organic pollutants in the reaction and the economic benefit of the recovered crystallization products as fertilizer needs further research.