Study On Performance And Mechanism Of Exogenous Substances To Alleviate High Anaerobic Load Acidification Of Food Waste

Anaerobic digestion is currently the most promising means of resource utilization,for the promotion of urbanization,food waste production has increased year after year,and the treatment efficiency needs to be improved.The goals of anaerobic digestion are twofold,to increase the decomposition rate and to recover as much energy as possible.However,the imbalance between acidifying bacteria and methanogenic bacteria for different substrate metabolism rates at high organic loads leads to serious acidification problems.In this paper,biochar,zero-valent iron and sponge iron were used as adjuvant substances and granular sludge was used as inoculated sludge,mixed and injected into high load（30 g/L volatile solids）kitchen waste to enhance the treatment efficiency by mitigating acidification;the effects of different adjuvant substances on maintaining the stability of anaerobic system were investigated at the optimal addition level,and their promotion was analyzed by changes in volatile fatty acids and microbial community structure.The mechanism was also analyzed by changes in volatile fatty acids and microbial community structure.The results showed that all three admixtures were effective in avoiding the accumulation of volatile fatty acids,with biochar being the most effective in reducing volatile fatty acids at the beginning of the reaction and zero-valent iron being more effective in reducing volatile fatty acids later in the reaction.It also enhances the cumulative methane production.The cumulative methane production of biochar,zero-valent iron and sponge iron were 312.40,268.56 and 255.60 mL CH₄/g VS,respectively,at the optimal additions,which improved 101.7%,77.8%and 69.2%,respectively,compared with the control group;the methanogenic stagnation periods of the three groups were shortened by 2.61,1.29 and 1.25 d.The objectives of anaerobic digestion were two,to increase the decomposition rate and to recover as much energy as possible.However,the imbalance between acidifying bacteria and methanogenic bacteria for different substrate metabolism rates at high organic loads leads to serious acidification problems.In this paper,biochar,zero-valent iron and sponge iron were used as adjuvant substances and granular sludge was used as inoculated sludge,mixed and injected into high load（30 g/L volatile solids）kitchen waste to enhance the treatment efficiency by mitigating acidification;the effects of different adjuvant substances on maintaining the stability of anaerobic system were investigated at the optimal addition level,and their promotion was analyzed by changes in volatile fatty acids and microbial community structure.The mechanism was also analyzed by changes in volatile fatty acids and microbial community structure.The addition of adjuvants affected the abundance of microorganisms in the anaerobic system.The main archaeal community in the blank group was the hydrogen-nutrient-dominated Methanobacterium with a relative abundance of 44.15%,which was reduced to 26.17%by the addition of biochar;19.42%by the addition of zero-valent iron;and 20.98%by the addition of sponge iron.The methanotrophic bacteria Methanothrix,which was associated with direct interspecies electron transfer,increased from 26.12%to 46.05%,42.49%and 38.5%,respectively.Moreover,biochar enhanced the abundance of Bacillus and Clostridium,and iron zerovalent and iron sponge enhanced the abundance of Lactobacillus.The diversity and homogeneity of the anaerobic system decreased in the presence of the three types of admixtures compared with the blank group,which proved that the admixtures could reduce the competitive effect of other microorganisms on organic matter.The variation pattern of pH and redox potential showed that zero-valent iron added to the anaerobic system preferentially provided electrons to methanogenic rather than H⁺,and the presence of methanococcus Methanosphaera could directly use zero-valent iron as an electron donor to receive electrons for direct reduction of CO₂or HCO₃^-by biosequencing.Sponge iron and zero-valent iron enhanced the relative abundance of Methanosphaera by 14.70%and 21.04%,respectively,but biochar did not contribute to Methanosphaera.