Enhancement Of Dry Straw Fermentation By Enriched Propionate Methanogenesis

The annual production of straw in the northeast of China is huge,and there are unfriendly treatment methods such as burning of straw-like biomas.Anaerobic fermentation of straw to produce biogas is one of the main ways of resource treatment currently.At present,the domestic fermentation method is mainly wet anaerobic,making the unit volume of the digester processing straw capacity is limited.Dry anaerobic fermentation has the characteristics of high concentration,large pool capacity gas production rate and low amount of fermentation liquid produced,which is more suitable for areas with abundant straw production.However,during the operation of dry anaerobic fermentation,the start-up period is long and the fermentation system is prone to volatile acid accumulation,leading to acid inhibition and eventually system destabilisation and even fermentation failure,which severely limits the promotion and application of anaerobic dry fermentation in the field of integrated straw treatment.In order to solve the above problems,this study used straw as the main raw material and used the propionate degradation methanogenic obtained by our group in the early stage of domestication as bioaugmentation agents to investigate the effect of bioaugmentation agents on the gas production performance of sequential batch anaerobic dry fermentation and semi-continuous anaerobic fermentation of straw.The optimal amount of bioaugmentation addition was determined through sequential anaerobic fermentation experiments,and the promotion effects of the propionate degradation methanogenic,straw fermentation liquid,nano-zero-valent and biochar additives were compared and analysed using semi-continuous anaerobic fermentation experiments.The main results of the study are shown below.（1）In the sequential batch anaerobic fermentation experiments with straw,the effects of different propionate degradation methanogenic additions on the methanogenic potential were compared,and the results showed that the higher the addition of the bacterial flora,the higher the cumulative methane production rate.The maximum bioaugmented methanogenic yield was achieved at 199.77 mL g^-1VS when the bacterial broth addition was 7.5%（VS broth/VS straw）.increasing the batch concentration to TS=20%continued to increase the methanogenic efficiency.The addition of propionate degradation methanogenic bacteria accelerated the start of anaerobic dry fermentation compared to the blank control.The modified Gompertz equation indicated that the addition of different doses of propionate degradation methanogenic bacterial lines could effectively shorten the start-up delay period and effectively increase the methane production rate.（2）Sequential batch experiments were conducted with two batches at TS=15%and TS=20%respectively.The group with bioaugmentation was able to start successfully regardless of the concentration range.The blank group failed to start in the TS=20%batch.The pH of the bioaugmented group fluctuated between 6.41 and 8.06 and ammonia nitrogen（TAN）was stable up to 1300 mg L^-1.The group with 7.5%bacterial solution addition（VS bacterial solution/VS straw）achieved 50.14%chemical oxygen demand（COD）degradation.The blank control group had a pH of 4.97,where significant acid inhibition occurred and there was little change in COD.（3）A comparative analysis of continuous anaerobic fermentation experiments was conducted to determine the effect of adding four types of propionate degradation methanogenic,straw fermentation broth,nano-zero-valent iron and biochar on promoting continuous anaerobic dry fermentation.The results showed that the bioaugmented system with the addition of propionic acid methanogenic bacterial line had the best gas production,and when the feed concentration TS was20%,the reaction system maintained stable operation for at least 3 HRT with an average daily methane production rate of 167.98 mL g^-1VS,which was 2 times and 2.75 times higher than that of the enhanced group with straw fermentation broth and the blank control group（non-bioaugmented group）,respectively.（4）In successive experiments where TS was raised from 10%to 20%,the bioaugmented treatment group showed stable chemical indicators,including lower volatile fatty acid concentrations（VFAs）,with VFAs concentrations consistently less than 1500 mg L^-1throughout the reaction cycle.the blank control group experienced severe acid accumulation at dry fermentation feed concentrations,including an average acetic acid concentration of 1441 mg L^-1at the last HRT It is evident that the addition of propionate degradation methanogenic can effectively degrade VFAs,especially acetic acetate and propionate,and lift the acid inhibition phenomenon.