Effect Of Anaerobic Co-digestion Of Food Waste And Landfill Leachate On Process Stability And Biogas Residue Performance

Anaerobic digestion（AD）is a major technology for food waste（FW）treatment in China.However,the mono-digestion of FW has some bottlenecks,such as lack of trace elements,ammonia inhibition and poor process stability.At the same time,there are a large number of domestic waste entering the landfill site in China.The leachate generated by landfill has high concentration of pollutants and the treatment is difficult,but it is rich in trace elements,humus and other substances required by FWAD system to resist ammonia stress.At present,the rise of solid waste venous industrial park provides convenience for the co-digestion of two types of waste.In order to clarify the effect of FW and leachate co-digestion on the performance of anaerobic digestion system,the characteristics of biogas residue and its utilization,this study first explored the effect of co-digestion on AD performance through batch experiments,and determined the appropriate co-digestion strategy.Subsequently,the physical and chemical properties,process stability and the influence on the properties of biogas residue of the co-digestion system under long-term operation were tested in the semi-continuous experiment.Finally,combined with the analysis of microbial community,the causes of performance differences between mono-digest and co-digest systems were explored.The main conclusions of this study are as follows:（1）The batch experiments showed that the gas production kinetics and gas production increased when FW was co-digested with leachate at an appropriate proportion,and the comprehensive performance was the best when the addition of leachate was 40%.At this time,the methane yield of the system reached 365.31 m L/g VS,which was significantly higher than that of the mono-digest group（p<0.05）.The effective digestion time was shortened to 8.07d.In addition,there was no significant difference in dehydration performance and plant toxicity between biogas residue in two different systems.E₄/E₆ increased from 4.35 to 4.50,indicating that the degree of humification of biogas residue was improved in co-digest group.（2）Long-term experiments were carried out in semi-continuous systems,and it was found that the stability of the co-digest system of FW and leachate was better than that in the mono-digest system.When the ammonia nitrogen concentration in the mono-digest system reached 2046.17 mg/L,TVFA gradually accumulated,and the gas production performance continued to decline,and eventually cause complete instability.In contrast,the ammonia nitrogen concentration of the co-digest system was higher than that of the mono-digest system.When the ammonia nitrogen was accumulated to 2093.07 mg/L,the methane yield decreased slightly from 0.46 LCH₄·g VS^-1 to 0.35 LCH₄·g VS^-1,and the TVFA was slightly accumulated to 3736.53 mg/L,but the performance of the system recovered after a short period of adaptation,indicating that the co-digestion of FW and leachate can improve the tolerance to ammonia nitrogen,and has stronger stability in the long-term operation.（3）When studying the effect of co-digestion on the performance of biogas residue in semi-continuous system,it was found that there was no significant difference in dehydration performance and plant toxicity between co-digest system and mono-digest system（p>0.05）.The highest contents of arsenic,mercury,lead,chromium and cadmium in biogas residue were 2.67±0.02,0.17±0.01,19.71±0.01,7.34±0.19 and 1.56±0.011 mg/kg,respectively,which were much lower than the limits in the relevant standard,and there was no continuous accumulation during the long-term operation.In addition,the degree of humification of co-digest system biogas residue is significantly improved,which has positive significance for its utilization.（4）Propionic acid degrading bacteria Pelotomaculum,butyrate and other long-chain fatty acid degrading bacteria Syntrophomonas were significantly enriched in the co-digest system under ammonia stress,while the abundance of Pelotomaculum decreased and Syntrophomonas fail to proliferate in the mono-digest system.The strengthen of hydrogenesis and acetogenesis stage in anaerobic digestion,avoiding the accumulation of long chain VFAs such as propionic acid may be the key to relieve ammonia inhibition and enhance system stability.