| Crop straws are the most abundant and renewable biomass resources for biogas production in China. However, there are still some problems about anaerobic digestion of crop straws, such as inadequate degradation of substrate and low efficiency of biogas production. Successful development of anaerobic digesters involves the startup of new digesters, which requires establishment of suitable environment and microbial populations needed to achieve the desired performance. However, the enrichment process of microbs can take considerable time as the methanogenic populations and activities are low, also the costs for storing and transporting of the sludge are very expensive. Aiming at these problems, the objectives of this study are to develop physical and chemical pretreatment technology of corn stover, such as the combined application of steam explosion and alkaline pretreatment, to determine the methane production rate and yield, to estimate the bioconversion potential of co-digestion from sweet potato vine and dairy manure, and to estimate the methanogenic activity of thermophilic anaerobic sludge during process and storage. The main results were as follows:Steam explosion and further treatment by NaOH or KOH with various alkaline loading were used to pretreat corn stover to enhance the anaerobic digestibility. The results of pretreatment indicated that lignocellulose structure subjected to different degrees of damage. The ligin and hemicellulose of pretreated corn stover were decreased by 18%-73% and 11%-76%, respectively. It was found that, under the same base concentration, NaOH had the higher efficiency over KOH on ligin and hemicellulose removal from alkaline treated corn stover, however, only similar capacity of ligin elimination was observed from steam-exploded and further alkaline treated stover. The maximum methane production rate of corn stover was significant improved by 44%-258% after the separate or combined application of steam explosion and alkaline pretreatment. Also, in contrast with corn stover, the digestion time of T80 from pretreated stover was shortened by 5 to 11 days. The cumulative methane yield of pretreated corn stover was increased by 1.0%-24.6% after stover was treated by 15% and 20% base loading.Compare with dairy manure (DM), sweet potato vine (SPV) had higher methane production rate during the digestion process of biochemical methane potential, and the cumulative methane yields of SPV and DM were 208.5%和 194.5 mL/g VSadded, respectively. To investigate the effect of VS ratio of SPV and DM on the biogas production of co-digestion, mesophilic batch anaerobic digestion was performed at 50 g-VS/L loading. It was fould that co-digestion of SPV and DM showed positive synergistic effect during the first 20 days of batch process, also shorter digestion time of T80 was observed in all the co-digestion reactors. To reveal the relationship between organic loading and the methane productivity, three organic loadings including 25,50 and 100 g-VS/L were investigated under two SPV to DM ratios (5:5,2:8) using batch digestion. Our further result showed that higher volumetric methane productivity was improved in high-loading reactors, while the specific methane yield decreased.Centrifugation and further vaccum rotary evaporation were used to reduce the moisture content from thermophilic anaerobic sludge, which were obtained from municipal wastewater plant (MS) and biogas plant using food waste as substrate (BP). In the batch digestion, the ratio of food waste and sludge (S/I Ratio) was 1:1 based on VS. The results showed that the processed sludge had lower maximun methane production rate than the corresponding original sludge, and all the anaerobic digestions were successful except the one using centrifuged and further evaporated BP sludge as inoculum.Two types of BP condensed anaerobic sludges, which contained 82.0% and 71.5% of moisture content by centrifugation and further vaccum rotary evaporation, were stored for 2 and 4 months under 20±2℃. Both food waste and non-fat dry milk were used as substrate and the S/I Ratio was 1/2. It was found that fresh unprocessed sludge had the highest methane yield and the yields of both unprocessed and processed sludges decreased during storage by 1-34%, however processed sludges seemed to regain some activity after 4 months of storage as compared to samples stored for only 2 months. Maximum methane production rates obtained from modified Gompertz model application also increased between 2-month and 4-month processed samples.The BP centrifuged sludge was stored for 10 months under different temperatures including 7℃, 20 ℃, and 55℃. Glucose, acetic acid and food waste were used as substrates to determine the effect of storage temperature on the methanogenic activity of condensed sludge and to estimate the recover rate of microbial activity in the processed sludge by two batch digestions. It was found that the centrifuged sludge stored at 7℃ reached the highest methanogenic activity and the samples stored at 55℃ obtained the fastest recovery rate of microbial activity. |
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