Malodorous Gases Production From Food Wastes Decomposition By Indigenous Microorganisms

China's rapid economic development has accelerated the process of urbanization and improved people's living standards.The rapid development of the size,quantity and population of cities leads to economic prosperity.Nevertheless,at the same time,the acceleration of urbanization directly leads to a large increase in the total amount of municipal household waste,especially in large and medium-sized cities.Volatile organic compounds?VOCs?produced during the degradation of food wastes may harm to the health of people and create annoyance in adjacent communities.In this thesis,therefore,we selected typical non-recyclable and biodegradable food wastes carry out the research during the food waste decomposition process in the lab by investigating the components and variation of malodorous gases produced during the decomposition of these different food wastes;studing the evolution of bacterial community structure at the same time;and interpreting the relationship between the malodorous gas emission and bacterial community in the fermentation of food wastes.The main contents are as follows:?1?Firstly,we comparatively investigated the malodorous gases production from the decomposition of six groups of food wastes and each group consist of single food waste.That is,three kinds of vegetables?onion,watercress and pepper?and three kinds of meats?fish,chicken and pork?were selected in parallel in a self-made reactor to carry out the fermentation experiments.The characteristics of released VOCs during fermentation were monitored.The study found that throughout the onion fermentation process?90 days?,the main released VOCs were oxygenated VOCs?OVOCs?,accounting for 59.4%of all released VOCs,followed by sulfur-containing VOCs?VOSCs?,accounting for all 26.6%of the VOCs released and ethyl acetate accounted for 62.9%of all OVOCs.Comparatively,the watercress mainly releases VOSCs during the fermentation,accounting for 86.4%of VOCs released,and trimethyl trisulfide accounts for 43.5%of VOSCs.During the whole period of fermentation of pepper,the most detected VOCs were OVOCs,accounting for 51.5%of all released VOCs,followed by VOSCs accounting for 41.8%of all released VOCs,and ethyl acetate accounting for 34.7%of the released OVOCs.The three kinds of vegetables all released the highest VOCs emission flux on the 10th day of decay fermentation,which were 133.8,508.2 and 136.4?g·kg^-1·h^-1.During the entire cycle of meat fermentation?90 days?,the mainly released VOCs were VOSCs for all three kinds of meats,accounting for 67.4%,72.8%,and 76.2%of chicken,pork,and fish,respectively.Trimethyl trisulfide is the main VOSCs,accounting for 67.2%,78.3%and 80.1%of the VOSCs released by chicken,pork and fish,respectively.On the fourth day,fish had the largest emission flux of VOCs,reaching 4289.2?g·kg^-1·h^-1,chicken and pork had the largest emission flux of VOCs on the 10th day,which were 2648.2 and 2054.9?g·kg^-1·h^-1 respectively.?2?Further,we comparatively investigated the malodorous gases production from the decomposition of three group of the mixed food wastes and each group consist of mixed food wastes including mixed fruits,mixed vegetables,and mixed meats.The VOCs emitted from these decomposition food wastes and their microbial communities were measured in three individual 57-L reactors for 61 days.Total of 232.8,373.5,and 191.1?g·kg^-1·h^-1 VOCs with OVOCs?57.6%?,VOSCs?58.6%?and VOSCs?54.9%?as the main group were detected during fruit,meat and vegetable fermentation,respectively.2-Butanone?55.1%?and ethyl acetate?13.8%?were the two most abundant VOCs from fruit wastes,while dimethyl sulfide?68.0%and 26.6%?and dimethyl disulfide?89.2%and 10.1%?were in vegetable and meat wastes.The predominant Firmicutes represented 93.0%–99.9%of the bacterial communities of meat decomposition,while Firmicutes and Proteobacteria were the dominant phyla throughout the fruit digestion process.Proteobacteria?16.9%-83.6%?was the dominant phylum in vegetable wastes,followed by Bacteroidetes,Firmicutes,and Actinobacteria.Malodorous VOCs emissions were highly affected by microbial activity,the abundant Weissella,Leuconostoc and Enterobacteriaceae in vegetable wastes showed correlation with carbon disulfide and dimethyl sulfide,while dominant Peptococcus,Bacteroides,Lactobacillales and Peptoniphilus in meat wastes was related to dimethyl disulfide.Overall,significant differences and correlation between VOCs emission profiles and bacterial communities among different food wastes decomposition were observed.Overall,these results contribute to a more comprehensive understanding the relationship between microbial community dynamics and malodorous VOCs emission,which will definitely provide useful information for waste management and malodorous gas control.