| Agricultural waste is originated from extensive sources,and it is an important feedstock for biogas production.This study was evolved around the subject of enhancement of efficiency of production of methane through anaerobic digestion of mixture of crop straw and livestock manure,based on the traditional technique of two-stage anaerobic digestion,the characteristics and principle of microaerobic hydrolysis and acidification had been studied and optimized under different control conditions,and a new mode suitable for the methane production by anaerobic digestion of agricultural waste with a high solid content was explored.Firstly,the effect of different solid content and oxygenic states on the substrate digestion and organic acid production was studied,and its mechanism of hydrolysis and acidification was also studied.Acidogenic phase aeration can significantly elevate the efficiency of lignocellulosic substrate(P<0.05),but with the elevation of solid content,the difference between VS removal rates disappeared when the solid content was high due to the effect of feedback inhibition by hydrolysate.On day 2 after acidification,the production rate of organic acid on a microaerobic condition reached up to 3684 mg/(L d).The result of rate of biogas production was optimized based on response surface,a maximum rate of biogas production can be achieved on the condition of high solid content(TS = 15%TS),Microaerobic(DO = 0.2-1 mg/L),and 48 h of hydrolysis and acidification,the non-airtight microaerobic hydrolytic acidified reactor was suitable for the methane production of agricultural waste;The study on effect of solid content,temperature and mixing mode with the microaerobic hydrolytic acidification has proved the crucial role the high solid content played in promoting the production of organic acid,the temperature and mixing mode played a significant role in the production of organic acid during the middle and late stage of acidification(P<0.05),the efficiency(k)can be increased by 217.9%and 290.5%by the degradation of cellulose and hemicellulose during the initial stage of hydrolysis and acidification;To further improve the efficiency of hydrolysis of substrate,the effect of straw particle size and pH control of hydrolytic acidification had been studied and optimized.It was revealed by the result of statistical analysis that,the straw particle size was significantly positively correlated with the VS reduction rate in the process of hydrolytic acidification(P<0.01),the effect of pH control on substrate degradation was insignificant,while pH was significantly positively correlated with the production of organic acid(P<0.01),the straw particle size was not the main factor responsible for the organic acid production.The efficiency of hemicellulose degradation will be facilitated when pH = 8,where the maximal efficiency of organic acid production was 2.3 g/(L d).Moreover,the yield of organic acid reached the maximum,9.5g/L on day 9 after acidification when pH equaled to 11.In a comprehensive consideration of efficiency of hydrolytic acidification and processing cost,the subject can be used for methane production when it is processed for 2 days on a condition that the medium grain size is used and pH = 8 during the acidogenic phase;In this study,the thermophilic microbial consortia MC1 was inoculated into a complex open environment(unsterilized and sterilized systems)to evaluate the feasibility of bioaugmentation to improve acidification efficiency.The results indicated that the hemicellulose degradation rate and organic acid concentrations increased significantly by two-fold and 20.1%(P<0.05)on day 3,respectively,and clearly reduced the loss of product.Finally,the acidogenic fluid improved methane yield significantly(P<0.05)via bioaugmentation.However,the bioaugmentation is disappeared gradually after day 5;The characteristics of microbes affected by different factors under microaerobic hydrolysis and acidification was revealed by a method of Miseq,and it was discovered that,the microbes was closely related to the change in temperature and pH in the different operating system,when the acidification occurs in a condition where the temperature is high and pH is low,Closridium is the predominant bacteria,while Prevotella is the predominant one when the temperature is medium.The abundance of Bacteroides quickly raises when the system pH tends to be neutral,the increase or decrease in pH will reduce the diversity and quantity of microbes,while in the process of Bioaugmentation in a complex environment,Microbial consortia MC1 was detectable in the early stage of acidification,5 days later,the cow dung microbes regained its predominance,the disappearance of MC1 had significantly reduced the efficiency of lignocellulose degradation;High solid content can significantly improve the yield of organic acid,a semi-continuous high-solid content two-phase anaerobic digestion technology had been established,Acidogenic phase was designed in a non-airtight manner and operated on a microaerobic condition,the acidified liquid after solid-liquid separation was used for production of biogas,the acidified residue was recycled for rice seedling substrate,and this two-phase anaerobic fermentation on a condition of different temperatures and total slurry circulation was studied.The result showed that,the effect of temperature and slurry circulation on the VS reduction was insignificant under a high solid content(P>0.05),the production of organic acid was stabilized after 10 days of operation,the use ratio of organic acid during a slurry circulation process was 60-90%,mesophilic temperature of slurry circulation was conducive to the maintenance of a high capacity biogas production rate,which was 1162.2 mL/L reactor/d,and the stability was improved.The culture of seedling with acidified digestate was markedly superior to the feedstock,digestate(cow dung)and soil,having a promising application prospect.A new mode of methane production with agricultural waste based on total slurry circulation with biogas production,and seedling substrate of acidified digestate was established. |
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