| Solid-state anaerobic digestion(SS-AD)is an effective way to recover renewable clean energy from solid organic waste such as straw,animal manure,and kitchen waste,etc.,at the solid content of 20%-40%.However,due to the high solid content and high organic loading rate,mass transfer in the digestion material is difficult,which can easily lead to local acid accumulation.Excessive acid accumulation will inhibit the growth and metabolic activity of methanogens,and then aggravates the accumulation of the intermediate acid.In view of the above problems,the abundance of acid-resistant methanogens in the inoculum was enriched gradually by acetic acid acclimation and the effects of initial microbial community structure on the evolution of microorganism population and SS-AD performance were studied.The main research content and conclusions are as follows:1.Effect of acetic acid acclimation on the microbial community structure in inoculum.Effluent collected from a liquid anaerobic digestion was acclimated by adding acetic acid and decreasing p H gradually until it can produce methane quickly and stably at p H 6.0.Archaea and bacteria community structures in the original sludge and acid-resistant sludge were analyzed by metagenomic sequencing method.The results showed that the diversity of methanogenic archaea community was reduced and the community structure changed significantly during acclimation.Methanosarcina,one of the acetotrophic methanogens,was significantly enriched and its relative abundance was increased from 4.2% to 58.1%,becoming the dominant archaea in acid-resistant sludge.However,the abundance of hydrogenotrophic methanogens decrease to varying degrees,and the dominant methanogenic flora in the sludge transformed from hydrogenotrophic methanogens to acetotrophic methanogens.The predominant bacteria in the sludge before and after acclimation were both Firmicutes and Bacteroidetes,the former is mainly degraded cellulose and hemicellulose,and the latter is mainly degraded protein.The abundance of Firmicutes increased from 48.8% to 61.7%,while the abundance of Bacteroidetes decreased from 30.1% to 16.9%.2.Effect of initial microbial community structure on the performance of SS-AD process.The original sludge and the acclimated acid-resistant sludge were mixed at the ratio of 1:0,3:1,1:1,1:3,and 0:1.And then five inocula with different microbial structure were obtained.SS-AD process were conducted using dry corn straw as feedstock at 37℃.The results showed that the reactors innoculated with acid-resistant sludge started up quickly,and the methane content and daily biogas yield reached to relatively high levels in the early stage of digestion.3.Effects of initial microbial community structure on the evolution of microbial communities during SS-AD.The results of metagenomic sequencing showed that the abundance of Methanosarcina,an acetotrophic methanogens,was maintained at a relatively high level in the reactors of fully acid-resistant sludge,and improved the start-up rate and relieved the acid-accumulation in dry anaerobic digestion process.Methanosarcina in the reactor of the completely original sludge showed an upward trend,and the relative abundance reached 71.63% on the 21 st day,indicating that the fermentation process is also a domestication process,and its community composition was similar to that obtained through acclimatization of acetic acid.This showed that the acclimatized inoculum is suitable for solid-state anaerobic digestion of dry straw.4.Effect of acetic acid acclimation of inoculum on SS-AD characteristics of different substrates.Dry corn straw and acidic silage straws were selected as substrates for SS-AD experiments.Inoculum amounts were selected from four levels of 10%,15%,20%,and25%.The results show that for corn stover,when the acid-resistant sludge is used as an inoculum,it can start normally under low inoculation(10%),and the gas production performance is good.The methane production of accumulated sludge can reach 82.68 L/kg VS·d compared with the original sludge treatment group under the same inoculation volume,the start-up time was 13 days earlier and the gas production was about 60% higher.This shows that the acid-resistant sludge has strong adaptability to dry stalks and can improve the problem of high inoculation amount in SS-AD;for silage straw,25%inoculum size is a critical value,below 25%,acid-resistant sludge and raw sludge treatment will inhibit the production of gas due to acidification;at 25%,methane production of acid-resistant sludge was significantly higher than the original sludge. |
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