Study On Optimization Of Biogas Slurry Treatment Process In A Centralized Aquaculture Manure Sewage Anaerobic Fermentation Facility

China is a large country of livestock and poultry breeding and consumption,with a large scale of livestock and poultry breeding and a large amount of livestock waste discharge.The concentration of pollutants in the fecal sewage is high.If it is discharged without proper treatment,it will cause serious environmental pollution and affect human life and natural ecology.In 2017,the Ministry of Agriculture issued the action plan for the resource utilization of livestock and poultry manure(2017-2020),and proposed seven treatment technology models for the livestock manure.Among them,the technical mode of waste treatment for large-scale livestock and poultry farms is to realize the energy utilization of excrement and sewage through centralized anaerobic fermentation.The key to the stable and continuous operation of this technology mode is the proper treatment of biogas slurry.In this study,the pretreatment + membrane separation method was used to optimize the process of the biogas liquid produced by a centralized livestock and poultry breeding anaerobic fermentation project,and the technical possibility of discharging the permeate liquid up to the standard after treatment and using the concentrated liquid as liquid fertilizer was explored.The high concentration of suspended solids(SS)in anaerobic fermentation biogas is an important factor limiting its utilization or subsequent treatment.In this study,the coagulation method as the core,the centrifugal separation as the solid-liquid separation method,supplemented by sand filter and security filter guarantee the pretreatment method to remove SS in the biogas slurry.The results show that the SS concentration can be reduced from the initial 34900-43600 mg/L to 4500-5300 mg/L by coagulation centrifugal separation,and the SS concentration of effluent can be reduced to 2300-2500 mg/L by sand filtration security filter.In the coagulation treatment,PAC and PFS are the suitable coagulants,PAM is the suitable flocculant;the better formula of sand filter stage is to fill 50 cm in the lower layer of 4?6 mesh and 50 cm in the upper layer of 30?40 mesh.In view of the pretreatment effluent,this study further investigated the treatment effect of microfiltration + nanofiltration membrane separation.The results of the influencing factors experiment and continuous operation experiment show that the effluent quality can meet the discharge requirements of the standard for irrigation water quality(GB 5084-2005)after the combined microfiltration and nanofiltration membrane separation treatment.The average concentration of COD,ammonia nitrogen and total phosphorus in effluent is 32 mg/L,347 mg/L and 6 mg/L respectively.The proportion of concentrate and permeate after double membrane treatment is about 4:6.Except for the low content of organic matter in concentrate which needs further compounding of materials,other components meet the requirements of biogas fertilizer(NY/T 2596-2014).The combination of citric acid and sodium hypochlorite with concentration of 2% and 0.1% was used to clean the microfiltration membrane and nanofiltration membrane.After cleaning,the recovery rate of membrane flux can reach over 93%.