Kinetic Modelling And Parameters Optimization From Biochar-mediated Co-anaerobic Digestion

China has produced volumes of straw and livestock manure wastes every year,at the same time,the comprehensive treatment efficiency is low,which has seriously restricted the development of related industries.In contrast,the traditional anaerobic digestion?AD?technology used in the treatment of agricultural and animal husbandry wastes,has long operation time,low total solid?TS?concentration and easy to cause inhibition.To solve above problems,some scholars proposed to add biochar to AD in order to improve the treatment efficiency as well as enhance stability of the system.However,most researchers focused on mono-digestion with biochar,and paid attention to the micro-mechanism of biochar adsorption and microbial enrichment.In this study,two kinds of wastes:swine manure and corn straw,were selected.After adding biochar,response surface method was used to determine the proportion of added substrates,and kinetic models were used to analyze the change of methane and main components in the substrate.Finally,the change of main components in substrates along with the methane production was analyzed.The main contents and conclusions are as follows:?1?The characteristics of co-digestion of swine manure and corn stalks with biochar added.In this chapter,swine manure and corn straw were selected as substrates,and experiments were carried out based on the principle of single variable.The effects of TS of mixed raw materials,carbon nitrogen?C/N?ratio and biochar addition on co-digestion were explored respectively.Besides,the daily methane production,the methane content,the cumulative methane production and the solvable chemical oxygen demand?s COD?of digestate were analyzed.The results showed that:with the increase of TS in substrates,the cumulative methane production first increased and then decreased.High TS leads to the increase of s COD in the middle and later stages.The first peak of daily methane production will increase and its arriving time will be advanced if TS in substrates is suitable.The increase of C/N ratio of feedstock results in the decrease of the first peak value and the increase of the second peak value,but the rising C/N has no significant effect on the methane content.Therefore,high TS and low C/N ratio will reduce the methane production efficiency and greatly improve the s COD of digestate,while adding biochar can effectively improve the initial methane content.?2?The parameter optimization of co-digestion of swine manure and corn stalks with biochar added.This chapter uses the method of Central Composition Design?CCD?,taking the TS?x₁?,the amount of pyrolytic carbon added?x₂?and the C/N ratio?x₃?as independent variables,the regression model of methane yield?y?at the confidence level?=0.1 is y=267.22+10.08x₁+10.37x₂+7.96x₃-42.90x₁²-14.09x₂²-16.03x₃².The results show that the fitting effect of the model is good through the goodness of fit analysis,residual analysis,disturbance analysis and other statistical evaluation.Additionally,the order of importance of three factors was TS>C/N>biochar addition.The optimal TS,biochar addition and C/N were 6.18%,8.73%and 21.69,respectively,and the methane production rate was 269ml/g VS.The relative error of the data obtained from the validation test accounts for 0.6%of the test value,and the deviation between the test value and the predicted value of the model is less than 5%.Therefore,the model obtained in this chapter is reliable and can be used to describe the variation of methane yield with the total solid content,the amount of biochar added and the ratio of carbon to nitrogen.?3?The kinetic analysis of co-digestion of swine manure and corn stalks with biochar added.In this chapter,under the condition of TS of 6.18%and C/N ratio of 21.69,several samples of biogas and digestate were selected in both of the experimental group?with 8.73%biochar?and the control group?without biochar?.In addition,the degradation sequences and trend analysis of methane and four main components are carried out.The results showed that:at the confidence level of?=0.1,the cumulative methane production and starch degradation rate of the experimental group with biochar were significantly higher than those of the control group without biochar.The main degradation of the experimental group showed that the sequence of degradation was hemicellulose and starch degradation firstly,crude protein degradation later.The modified Gompertz equation can fit the cumulative methane production better in both the experimental group and the control group;the modified Gompertz equation and Logistics equation can fit the main degradation components better in both the experimental group and the control group.Therefore,by analyzing the parameters of the kinetic equation,it is clear that adding biochar can shorten the lag time and improve the efficiency of AD,furthermore,biochar also can promote the degradation rate of starch components largely in substrate.