Study On Anaerobic Digestion Performance Of Food Waste Enhanced By Iron-biogas Residue Biochar

With the improvement of economy and people’s living standard,the output of food waste in China has increased year by year.The food waste is characterized by high organic matter and water content,which can be converted into stable renewable energy by anaerobic digestion technology.However,the accumulation of volatile fatty acids（VFAs）and poor system stability often occur in the anaerobic digestion system of food waste,especially when the organic load is high.In this paper,biogas residue biochar（BRB）was innovatively prepared by biogas residue after anaerobic fermentation as raw material,and it was combined with zero-valent iron（Fe⁰）and modified with iron solution,respectively,to study the effect of Fe-biochar addition on the anaerobic digestion performance of food waste.The specific research was carried out from the following three aspects:（1）the anaerobic digestion performance of food waste by Fe⁰,BRB and Fe⁰/BRB addition;（2）BRB enhanced anaerobic digestion performance of food waste with different organic loads;（3）Enhanced anaerobic digestion performance of high organic food waste by iron-modified BRB.The main results are as follows:1)The effects of BRB,Fe⁰（nano-zero-valent iron n ZVI,iron powder IP）and Fe⁰/BRB on anaerobic digestion performance of food waste were investigated.The results showed that Fe⁰ supplementation promoted the methane production of anaerobic digestion of food waste,and the methane production reached 448.3±11.3 m L/g-VS when n ZVI was added,compared with the control group（390.5±2.9 m L/g-VS）by14.80%（P<0.05）,and the effect of n ZVI with smaller particle size was more significant than IP.By improving the degradation efficiency of organic matter,Fe⁰/BRB can provide a substrate for the smooth process of methane production,thus increasing the cumulative methane production（6.35～9.60%）and effectively shortening the lag period of methane production.Although BRB did not promote methane production,VFAs were consumed earlier in BRB groups,indicating the potential of accelerating VFAs consumption,which may be related to the timely utilization of VFAs by Methanosarcina,a highly enriched methanotrophic methanogenic bacterium.2)For VFAs accumulation and system acidification during anaerobic digestion of food waste under high organic loading,while BRB has the potential to promote rapid consumption of VFAs.Different organic loading gradients（VS ratio of substrate and inoculants:0.5:1,1:1,2:1,3:1）were set to study the effects of BRB addition.The study showed that the cumulative methane yield was the highest when the inoculation ratio was 1:1（375.5±8.4 m L/g-VS）in all blank groups.When the inoculation ratio was greater than 1:1,the system acidified due to VFAs accumulation,and the methane production process was inhibited.The cumulative methane production decreased with the increase of organic load,and the lag period of methane production was prolonged.BRB did not improve methane production at low organic load（inoculation ratio of 0.5:1）,but with the increase of organic load,the addition of appropriate amount of BRB could promote the increase of cumulative methane production.When the inoculation ratio was 3:1,5 g/L BRB supplementation（318.5±38.2 m L/g-VS）increased methane production by 21.37%compared with blank group（262.3±34.9 m L/g-VS）（P<0.05）.Microbial community analysis showed that the enrichment of functional bacteria such as Clostridium＿sensu＿stricto＿1 and Syntrophomonas may have contributed to the rapid depletion of VFAs,while Methanosarcina and other methanogenic bacteria contributed to the increase in methane production.3)In order to further improve the anaerobic digestion performance of BRB with high organic load,BRB was modified with Fe Cl₃ solution to obtain two modified biochar（1M Fe-BRB and 0.1M Fe-BRB）.The results showed that Fe-BRB addition could accelerate the degradation of organic matter and the consumption of VFAs,so as to alleviate the adverse effects of acid inhibition on methanogenesis,shorten the lag period of methanogenesis,and improve the stability and efficiency of system operation.The cumulative methane production in 0.1M Fe-BRB（434.3±12.7 m L/g-VS）and 1M Fe-BRB（427.8±7.5 m L/g-VS）groups was increased by 21.10%and 19.26%（P<0.05）,compared with the control group（358.7±10.2 m L/g-VS）,respectively.The rapid degradation of VFAs in Fe-BRB group may be related to the significant enrichment of bacteria such as Clostridium,while Syntrophomonas and Methanosarcina may promote the efficient methanogenesis through the direct interspecific electron transfer pathway.Particularly,the cumulative methane production in 0.1M Fe-BRB（434.3±12.7 m L/g-VS）and 1M Fe-BRB（427.8±7.5 m L/g-VS）groups was increased by 21.10%and 19.26%（P<0.05）,compared with the control group（358.7±10.2 m L/g-VS）,respectively.The rapid degradation of VFAs in Fe-BRB group may be associated with functional bacteria such as Clostridium＿sensu＿stricto＿1,while Syntrophomonas and Methanosarcina interact with each other and promote efficient methanogenesis through direct interspecific electron transport.In conclusion,BRB can accelerate the consumption rate of VFAs,and has a significant effect on methane production in high organic load anaerobic system.The effect of Fe⁰/BRB loading material is mainly to shorten the lag period of methane production.Compared with BRB,Fe-BRB can further alleviate the anaerobic acidification system with high organic load and promote the smooth process of methanogenesis.The above research results provide theoretical reference for enhancing the anaerobic digestion performance of food waste,and provide a new idea for resource utilization of biogas residue.