Study On Treatment Technology Of Biogas Slurry By Multi-Stage Membrane Process

According to the national plan for the development of grass-fed animal husbandry(2010-2020)published by the ministry of agriculture,China's animal husbandry products show a trend of growth,and the standardized breeding scale has been steadily promoted.Therefore,biogas project with anaerobic fermentation technology as the core has been widely applied and popularized.While producing biogas,biogas project will produce a large amount of biogas slurry with high contents of COD,SS and nutrients such as nitrogen,phosphorus,potassium,organic acid and humic acid needed by plants.The conventional treatment methods such as reduction of biogas slurry to the field cannot be widely popularized due to the limiting of storage and transportation conditions,low concentration of nutrients and other factors.Biochemical combination processes such as A/O,SBR,SBBR and BAF have been adopted for the purpose of standard discharge.However,due to the low B/C ratio and imbalance of C/N/P ratio,the project construction still faces the problems of temperature-sensitivity,large area and long period.The useful substances in biogas slurry still cannot be recycled and utilized.In this study,an integrated process with five kinds of membrane technologies was proposed to investigate the reduction,harmlessness and resourcing of biogas slurry.The experimental device of five-level combination treatment of biogas slurry was set up,and a lot of experimental research and data analysis were carried out.The following results were obtained from the experiments:(1)Microfiltration using ceramic membrane with a pore size of 200nm was firstly performed to remove the suspended materials presented in the biogas slurry and thus proving guarantee for the stability of the whole process.The turbidity of the treated effluent could be controlled below 2.5NTU.(2)After the treatment of combined process,biogas slurry changed from almost black turbid liquid to nearly colorless,clear and transparent.The COD,ammonia nitrogen and total phosphorus of the treated effluent were lower than 140mg/L,8mg/L and 3mg/L,respectively.These data reached the target set by this experiment and meet the requirements of"discharge standard of pollutants in livestock and poultry breeding industry GB18956-2001".(3)The removal of ammonia nitrogen by ceramic microfiltration membrane and nanofiltration membrane were inefficient and unsatisfied.The removal of ammonia nitrogen by the lowest pore size DTRO was also lower than 85%for the alkalinity of slurry.The effluent from the combined process of MF+NF+DTRO still could not meet the requirements of discharge standards.It was necessary to further remove of ammonia nitrogen by the process of degassing using super hydrophobic membrane,and the removal efficiency is 99.0%.(4)The resourcing of biogas slurry could be achieved through the treatment of multi-stage membrane process.The biogas slurry was separated into 1#concentrated of suspended solids,2#concentrated of humic acid and macromolecular organic compounds that can be used to configure humic acid fertilizer,3#concentrated of small molecule organic matter that can be used for configuration of foliar fertilizer raw materials,and 4#ammonium salt solution(ammonium phosphate can be mixed with the high concentrated humic acid and large or small molecule organics to produce nitrogen-phosphate fertilizer).(5)Based on the data of field testing,a project plan of 300 m3/day of biogas slurry treatment system was designed and the operating cost of engineering equipment and economy of the project were evaluated.The direct operating cost including labor,electricity and chemicals were about 42.18 yuan/m3.