Solid-state Anaerobic Digestion Characteristic Of Corn Stover And Metabolic Analysis

In order to improve the environment and make use of the wastes,taking the large amount of waste straw produced by our country every year to anaerobic digestion is of vital importance.Due to the variability and heterogeneity of the fermentation system,the regional difference of the substrates,mass transfer between solid and liquid phase,and the selection of fermentation process and conditions,additional with the lack of knowledge of solid state anaerobic digestion degradation mechanism and microbial metabolic process,the technology is practically limited.This paper aimed to do some explore with the substrate pretreatment and several suitable operational conditions.Through the analysis of some kinetic parameters and the changes of microbial community,the optimum technological conditions and the theoretical explanations were obtained.First of all,in the study of pretreatment of corn stover,the methods of milling(particle size of 2-3 mm),ensiling,KOH singly treating and combination were used,together with the device of Bioprocess and the condition of 20% TS(Total Solid).These experiments were conducted at 37?.Corn stover(CS)without any pretreatment had a low methane production,only 97.4 ± 10.4 mL/g VS,After ensiling or milling,the final methane yield increased to 111.1±4.8 mL/g VS and 105.1 ± 1.4 mL/g VS,while the cumulative methane yield of ensiling + milling reached 120.2 ± 3.3 mL/g VS.Thus it can be seen that pretreatment could not only improve the methane production,but also improve the stability of the system.The results of KOH treatment group showed the methane production of only 85.7 ± 2.3 mL/g VS.The VFA content in this group was about 4500 mg/L,much higher than other groups of 1000-2000 mg/L,inferring that there was a certain degree of acid inhibition.Secondly,based on the results of pretreatment,three batches experiments of SS-AD were executed each for 28 days,using ensiling corn stover as substrate and garage type reactor.Appropriately increasing solid content of substrate,reducing the spraying time and increasing spraying interval,not only could keep high methane production,but also could reduce water and energy consumption.In addition,make it much easier to deal with the residue in the subsequent processing.When the TS was 30%,the capacity of producing methane is better than 15% and 20%,the total methane production were 193.6 mL/g VS,148.9 mL/g VS and 133.2 mL/g VS,respectively.The spraying way of 6 min each time during the first two week,3 min each time during the third week and no spaying during fourth week,(6,3,0)for short,showed better methane production performance than(4,2,0)and(2,1,0),and the total methane production were 196.5 mL/g VS,186.5 mL/g VS and 128.9 mL/g VS,respectively.Similarly,when the spraying interval was 3 h,6 h and 8 h,the total methane production were 190.1 mL/g VS,188.2 mL/g VS and 130.1 mL/g VS,respectively.Therefore,considering the operational conditions and energy consumption as a whole,the optimal digestion conditions with the ensiling corn stover were total solid content rate of 30%,spraying way of(4,2,0),and spraying interval of 6 h.Finally,dynamic parameter analysis and microbial community structure of the above three batches experiments were carried out.Kinetic parameter analyzing results indicated that the eventually methane production was positive correction with the hydrolysis rate and acetic acid conversion coefficient,until the acid inhibition appeared.The maximum utilization of acetic acid and the microbial cell decay coefficient were also key parameters to control the internal reaction.Microbial structure analyzing results showed that the methanobacterium and methanosarcina had the highest abundance and strongest metabolism.During the process,the two microbial community showed the tendency of increase rapidly first and later became stable.Because of there was less spraying or no spraying in the last two weeks,many bacteria species multiplied.Although the proportion was not big,the effects could be not ignored.Along with the digestion,microbial community abundance and diversity were gradually increased,while uniformity was decreased.Besides,VFA and pH were important environmental factors that affected the strain content.After three successive experiments,the variation of each index was smaller and smaller,so did the influencing factors.Therefore,the ultimate leachate had the characteristic of small kinetic parameter fluctuation change,stable quality and better fermentation performance.