Anaerobic Digestion And Trace Metals Regulation Characteristics Of Cow Dung/Corn Straw And Its Dynamics

In recent years,with the growth of solid waste,the recycling and harmless of solid waste is a hot focus in environmental and energy field.The anaerobic digestion technology of solid waste has been widely applied for low cost and abundant sources.However,in the actual project,the lower biogas production is the key factor in this field.This study used the agricultural wastes as raw material.And the corn straw was pretreated by acid,NaOH,and ultrasound respectively,and used the different methods(such like SEM,IR,XRD)to analyse the broken structure.Digestion conditions were optimized by orthogonal experiment and the single factor experiment.The kinds and concentration of trace element were also optimized by the single factor experiment and the combination design of orthogonal and quadratic regression equation,and the effect of trace element on digestion was also explored in details.For digestion characteristic,the factors such as inoculum,diameter of corn straw and loading was investigated during the set-up and runing process of reactor.First,H2SO4,NaOH,frozen,ultrasound was used to damage corn straw,enhanced the accessibility of microorganism,shortened the digestion period and avoided acidosis;Corn straw was pretreated by 1%H2SO4,3%NaOH and 6%NaOH,respectively,and compared to control group,the content of cellulose and lignin in the pretreated groups increased,and the digestion period was shortened by 5 days,7 days and 5 days,respectively.The result showed that in freeze method the destruction of corn straw was a little,only the epidermis was destroyed.And the dilatational strain happened in internal structure of corn straw in freeze method.Ultrasound promoted the destroy of the internal structure of corn straw;?The optimum values of loading,the proportion of cow manure and corn straw,the volume of inoculum,diameter of corn straw were obtained by orthogonal experiment,and the optimum values were 46.67gVS/L,5:1,533.33mL/L,and<0.5mm,respectively;"?The degree of propionic acid accumulation was related to the proportion of corn straw at the 5th day in the digestion period,but it did not lead to acid suppressants;When the proportion of cow manure and corn straw was 2:1,compared to cow manure digestion and corn straw digestion,the highest yield of CH4 increased by 21.45%and 18.21%respectively;?Compared to the control,the best added concentration of re0,Fe2+,Co2+,and Ni2+ were 1500mg/L,250mg/L,0.3mg/L and 0.6mg/L,respectively,and the yield of CH4 increased by 29.58%,17.70%,16.05%,and 35.56%,respectively;The optimal combination of Ni2+,Fe0 and Co2+ were 0.58 mg/L,1200 mg/L and 0.34 mg/L;Appropriate concentration of trace elements promoted the metabolism of propionic acid or reduced the production of propionic acid.Compared to the control,optimal combination of trace elements obtained the higest value of CI-I4 efficiency(312.87mL/gVS),and digestion period was shortened by 0.85d,and the efficiencies of CH4 and CO2 biotransformation production increased 36.76%and 74.50%,respectively.In a word,this study determined the added concentration of trace elements in co-digestion,and the effect of iron,cobalt,and nickel on the digestion characteristic was studied by hydrolysis kinetic parameters and VFAs.The results in this study not only have a certain theorical significance,but also can improve the biogas efficiency of anaerobic digestion.