A Study On The Imbalanced Microecological Response Of Food Waste Anaerobic Digestion System

Food waste has a large output and complex composition,which poses a great threatto public health and environmental safety due to its rich organic matter content and perishability.At the same time,it is also a resource with huge biomass potential.Anaerobic digestion can not only eliminate its pollution characteristics,but also produce biomass gas,which has become one of the most competitive resource treatment methods of food waste.The existing research and practical engineering operation cases show that the stability of the anaerobic digestion system of food waste is poor,and the microorganisms in the system are easily affected by the disturbance of environment,load and oil,resulting in imbalance.In order to explore the microecological response mechanism of food waste anaerobic digestion system imbalance and seek the characteristic microbial early warning information indicating the stability of the system,response surface methodology and metagenomics technology were used to study the microecological response mechanism of food waste anaerobic digestion system imbalance,such as microbial community succession and metabolic pathway changes,and the indicator system was found The main conclusions are as follows:(1)The key factors of the stability of the anaerobic digestion system of food waste were determined by response surface analysis:temperature>Load>oil content;At the same time,the quadratic polynomial mathematical model of methane production rate of anaerobic digestion of food waste was established,and the ideal reaction conditions of methane production from anaerobic digestion of food waste were obtained as follows:medium temperature(40?),organic loading(3.0kg VS/(m³·d)),oil content(2%);In order to simulate the unbalance experiment of the system,the critical condition under the condition of this study is found out.(2)The results showed that the hydrolytic acidification bacteria changed from Pseudomonas,acidovora,parabacterioides,Thauera to aminobacterium and Clostridium before and after the imbalance;In this experiment,methanogenesis of acetic acid and ethanol was the main methanogenic pathway in the stable period of anaerobic digestion system,and methanothrix was the dominant methanogenic bacteria with high methanogenic efficiency;After system imbalance,the abundance of methanothrix decreased,then the abundance of genes related to CO₂ metabolismpathway in methane metabolism decreased significantly,and the abundance of methanoculleus increased relatively.Finally,an unbalanced microbial community structure system with high proportion of bacteria and few Archaea was formed in anaerobic digestion system.(3)According to RDA analysis,the process from stabilization to imbalance of the system can be divided into three stages:(1)the increase of organic matter content in anaerobic digestion system promoted the abundance of acid producing bacteria(mainly Pseudomonas,acidovora and parabacteroides),increased the content of volatile fatty acids(VFAs),decreased the total alkalinity(TA)and fluctuated the p H value slightly;(2)When TA decreased to a certain extent,p H decreased,VFAs accumulated slightly,and the abundance of acidogenic bacteria(mainly aminobacterium and Clostridium)increased,which further aggravated the acidification phenomenon;(3)The p H value decreased significantly due to the lack of TA,which led to the decrease of abundance of acidogenic bacteria suitable for alkaline hydrolysis,VFA degrading bacteria and main methanogens in anaerobic digestion affected by environmental acidification,resulting in the imbalance of microbial community structure system and system in anaerobic digestion system.In conclusion,the detection of abundance changes of"acidogenic bacteria suitable for acid hydrolysis"and"acidogenic bacteria suitable for alkaline hydrolysis"has a good early warning significance for the stable operation of anaerobic digestion system.(4)It was found that the metabolic pathways of acetic acid,propionic acid and butyric acid all responded to the acidification imbalance in the anaerobic digestion system of food waste;In acetic acid metabolism,the abundance of ACDA,a gene related to acetate Co A ligase(ADP forming)subunit alpha in pathway 4,and ALDH,a gene related to aldehyde dehydrogenase(NAD+)in pathway 6,changed significantly;In propionic acid metabolism,the genes ACDA,ACSS and the abundance of ACS of the major pathway related enzymes acetate---Co A ligase(ADP forming)subunit alpha and acetyl Co A synthetase changed greatly;The buk gene abundance of butyrate related enzymes,such as phosphate butyry and ltransferase butyrate kinase EPTB,showed an upward trend.At the same time,the synthesis of methane furan for CO₂ utilization in methanogenic metabolism is blocked,the energy metabolism pathway of methanogens is blocked,the abundance of key methanogens in stable period is decreased,the methanogenic pathway is blocked in the initial stage,and the system is unbalanced.