Microbial Response Of Anaerobic Digestion System Of Food Waste Under Ammonia Nitrogen Stress

The protein content in the kitchen waste is high,so its anaerobic digestion is easily affected by excessive ammonia nitrogen released by protein hydrolysis,which leads to a decrease in gas production performance,accumulation of intermediate products,and even complete instability.A comprehensive analysis of the mechanism of instability caused by ammonia inhibition in the anaerobic digestion system of kitchen waste is necessary to strengthen the anaerobic digestion process and ensure efficient and stable operation of the system.In view of this,this study set up two batch experiments.In this way,we can analyze the performance characteristics of the reactor and the microbial community succession process under different ammonia nitrogen concentrations,in order to reveal the key links of instability,find key microbial factors and ammonia-tolerant microorganisms,and judge whether the microbial communities can self-accidentally adapt to high ammonia nitrogen conditions.The main conclusions of this study are as follows:(1)In the first batch of experiments,the accumulated methane yield of the anaerobic digestion reactor decreased with increasing ammonia nitrogen concentration,the gas production rate decreased,and the methane acclimatization phase was prolonged.The methane recovery rates of ammonia nitrogen concentration reached 6000 and 7500 mg/L were 85.70% and 67.39%,respectively.The acid accumulation of propionate was observed in the two reactors.The concentration of propionate was still as high as 258.27,686.15mg/L at the end of the reaction.(2)In the second batch of experiments,whether the original ammonia nitrogen concentration was maintained or increased to a higher ammonia nitrogen concentration,the average methane yield in the reactor increased significantly and significant improvement in dynamics(acclimatization phase and gas production time)with the same ammonia nitrogen concentration.However,the acid accumulation phenomenon was not improved under high ammonia nitrogen(>6000mg/L).The concentration of propionate was 293.33-982.96mg/L at the end of the reaction.(3)Ammonia nitrogen stress has a great impact on microbial diversity.In terms of ? diversity,with the increase of ammonia nitrogen concentration,the Ace,Chao and Shannon indices of the community decreased significantly,and the Simpson index increased significantly,indicating that the richness and diversity of the community were reduced.In terms of ? diversity,clustering of each sample by PCA found that the higher the ammonia nitrogen concentration,the farther the microbial sample points were from the control group,indicating that different degrees of ammonia-nitrogen stress caused different succession of the community,and the height was high.The succession of microbial communities under ammonia-nitrogen stress was the same.(4)During anaerobic digestion,the abundance of hydrolysis fermentation bacteria increases with the increase of ammonia nitrogen concentration,and it is converted to microorganisms with strong hydrogen production ability,indicating that higher concentrations of volatile fatty acids and hydrogen are produced in the system.The acedogenic hydrogenogens Syntrophomonas and Pelotomaculum were inhibited at an ammonia nitrogen concentration of 6000 mg/L,and no alternative microorganisms with equivalent functions appeared,indicating the irreversibility of inhibition at this stage.At this time,the degradation ability of the system VFAs was affected.Methanogens are most strongly inhibited by ammonia nitrogen,and the overall trend is to decrease with increasing ammonia nitrogen concentration.Among them,methanogens were first inhibited by ammonia.At 3000 mg/L,acetic acid was observed to accumulate in the early stage of digestion.However,as the reaction time prolonged,the Methanosaeta were gradually replaced by Methanosarcina,and acetic acid was eventually consumed.Most of the microorganisms that can consume hydrogen are attributed to methanogenic archaea,and the relative abundance of the entire archaeal community and the increase of hydrogen production lead to an increase in the hydrogen partial pressure in the system.The contradiction between the increase in the abundance of acid-producing bacteria and the decrease in the abundance of acid-consuming bacteria,and the higher hydrogen partial pressure in the system that hinders the mutual degradation process of long-chain VFAs such as propionate.Together,them lead to acid accumulation in the anaerobic digestion process,which may be the key to process instability.(5)The key link of process instability under high ammonia nitrogen is the degradation of long-chain VFAs represented by propionate.The related mutual degradation complex is the key microbial factor found in this study.More attention is paid to the microbial flora that is mutually degraded by propionic acid/butyric acid,which can provide a new direction for process strengthening..