Anaerobic Digestion Of Co-fermentation Of Food Waste And Dewatered Sludge By Tar For Methanogenesis Inhibition And VFAs Production

Methanogen bacteria activities must be inhibited in this process for considerable VFAs productions during anaerobic digestion?AD?of biomass.Acidification,basification,aeration,heat-shock pretreatment,and a combination of that two or three were applied a few in parent inoculum of AD for methanogenesis inhibition.But the higher pH value and aeration will inhibit both methanogen microorganisms and other microorganisms;heat-shock pretreatment needs extra energy input.Besides,the most widely available method of methanogenesis inhibition was chemical inhibitor,involving adding 2-bromoethane sulphonic acid sodium salt?BES?in parent inoculum,showed stable performance in suppressing methanogens activities for the generation of VFAs and hydrogen.But the price of BES is expensive,resulting in extra cost in waste management making it not to be the best choice for methanogenesis inhibition and making it just be applied in lab-scale researches.Therefore,cheaper and more stable methods for methanogenesis inhibition are needed to be explored.Biomass tar as the undesirable by-product producing in biomass pyrolysis/gasification process,was used as the methanogenesis inhibitor in this study.The aim of this study was to exam the effect of tar addition in anaerobic digestion for methanogenesis inhibition.To obtain the VFAs production accumulation and distribution.Besides,the impact on co-generation of biohydrogen in this study was also presented.Accordingly,this work was also conducted to discuss the microbial community and diversities in different methanogenesis inhibition conditions.Three gradient tar concentrations were added in reactors,7.0 g/L?T7?,15 g/L?T15?and 30 g/L?T30?,respectively,as compared with BES(R_BES),a chemical inhibitor.And Rco was set as the control without any methanogenesis inhibition measures.?1?The effect of tar on CH₄ production was examined.The two higher tar concentrations completely inhibited methanogenesis,while 570.59 mL/g VS CH₄ was produced in control and a small amount of CH₄?19.56 mL/g VS?was produced in R_BES in the latter period.?2?In order to explore the H₂ production under different methanogenesis inhibition measures,variations and accumulation of H₂ yields were analyzed.The yield of H₂ increased by adding tar in anaerobic fermentation.The highest H₂ yield was observed in T30,which was enhanced by 8.94-folds compared with that in Rco and 9.30-folds compared with that in R_BES.The increasing time of H₂ yields was postponed and prolonged with the addition of tar.?3?To gain the changes in fatty acids production after adding tar in AD,the composition of VFAs were analyzed.The tVFAs concentrations in T7,T15 and T30 were 44.3%,68.1%and62.4%in control?Rco?.The highest tVFAs concentration under all conditions was in T15,reached 5279.3 mg/L.VFAs productions were shifted towards more reactive and more valuable products by adding tar.The dominant VFAs were acetate and propionate in R_BES and Rco,acetate and n-butyrate in T7,and acetate,n-butyrate and caproate in T15 and T30.The highest n-butyrate concentration reached 2381.9 mL/L in T30,which was enhanced by 6.7-folds compared with that in Rco.And caproate presented in T30?1302.1 mL/L?and T15?1093.6mL/L?without extra electron donors.?4?To understand the influence of tar addition on AD,high-throughput gene sequencing of bacterial community and archaeal community were analyzed.The phylum Chloroflexi was involved in utilizing H₂ and producing propionate,the relative abundance of which increased from 8.31%of inoculum?Rin?to 17.01%in Rco.The hydrolysis and acidification bacteria,Firmicute were enriched in R_BES,T7,T15 and T30,the relative abundances of which enhanced by 17.46%,12.50%,26.16%and 12.91%compared with that in Rin.Likewise,the class Clostridia was responsible for the improvement of VFAs production,the relative abundances of which enhanced by 16.44%,5.41%,16.68%and 14.05%compared with that in Rin.The relative abundances of Actinobacteria in R_BES?3.52%?,T7?4.43%?,T15?2.17%?and T30?2.05%?were higher than in Rco?1.01%?.For different methanogenesis inhibition measures,metabolic types of methanogenesis were different.The acetoclastic and hydrogenotrophic methanogen Methanosarcina was inhibited in tar-adding conditions,resulting in the absence and decrease of CH₄.The relative abundance of in T7,T15 and T30 were 0.91%,0.06%and0.09%,but 14.50%in Rco.By adding chemical inhibitor BES,the abundance of acetoclastic methanogen decreased from 56.50%of Rco to 33.53%.