Study On Performance And Microbial Communities Between Dry And Wet Anaerobic Fermentation By Kitchen Waste

Kitchen waste contains large amount of organic matters like lipid and protein,which will cause a threat to the environment and human health inevitably.Anaerobic fermentation is the main research direction of kitchen waste recycling among many treatments of kitchen waste.Wet anaerobic fermentation consumes a lot of energy,and large amounts of effluent can cause secondary pollution.Compared with wet anaerobic fermentation,dry anaerobic fermentation has the advantages of low operating cost,no effluent,and its residue can be composted.However,the efficiency of mass and heat transfer in dry anaerobic fermentation system is low because of no flowing water,which is likely to cause obstacles of growth and metabolism of microorganisms.Stirring,to some extent,can solve these problems,but external force will destroy microbial flora.Rolling is used instead of stirring to make the substrate freely mixed in this study,which is believed to overcome these problems in dry anaerobic fermentation system.The performance of the reactor was verified by mesophilic temperature batch anaerobic fermentation and compared with stirred reactor and wet anaerobic fermentation.1.New design of anaerobic fermentation reactors.The whole equipment consists of fermenter and pre-fermenter.The effective volume of pre-fermenter and fermenter are 10 L.Substrate is added to the pre-fermenter first and air is exhausted by nitrogen.Then discharging substrate into fermenter.The effect of pre-fermenter is avoiding too much oxygen is brought into the fermenter.2.Batches dry anaerobic fermentation of kitchen waste at mesophilic temperature were operated by the new designed equipment(Reactor A)and a stirred fermentation tank(Reactor B).Results showed that methane content in the self-designed reactor was up to 74%.The main accumulated volatile fatty acids in the system were acetate and propionic acid.VS removal rate was up to 68.74%.Firmicutes was the absolute dominant bacteria in the fermentation system.The most important archaea was the Euryarchaeota.Methanosarcina which can utilize all three known pathways for methane production grows into an absolute dominant methanogen,followed Methanoculleus and Methanobacterium.3.Similar to dry anaerobic fermentation,biogas production of wet anaerobic fermentation(Reactor C)increased rapidly first and then decline.The peak value of methane content was up to 76%.The p H value decreased first and then increased.The accumulated volatile fatty acids in the system were mainly acetate and butyrate.VS removal rate was 53.11%.Firmicutes was the absolute dominant bacteria in the system.The most important archaea was Euryarchaeota.Methanosarcina was dominant methanogen genus,followed Methanoculleus,Methanobacterium and Methanocorpusculum.4.The results showed that a similar trend of two biogas production peaks in dry and wet anaerobic fermentation systems.Cumulative biogas production of dry system is relatively high,but retention time is much longer.Methane content fluctuates seriously in dry system.Variation trend of p H is similar in two systems.Accumulated volatile fatty acids in wet system are mainly acetate and butyrate,propionic acid and acetate in the dry system.VS removal rate in both systems are well.At phylum level,relative abundance of Actinobacteria,Proteobacteria and Spirochaetae are significantly higher in dry system.Methanosarcina is dominant methanogen in both anaerobic fermentation systems,followed Methanoculleus and Methanobacterium.Methanocorpusculum and Methanospirillum are only found in wet anaerobic fermentation systems,and Methanobrevibacter only exists in dry anaerobic fermentation systems.5.It was successfully verified that the type of rolling reactor which is new designed can solve kitchen waste efficiently by dry anaerobic fermentation,and it was better than stirred dry anaerobic fermentation system and wet anaerobic fermentation system.Large-scale verification can be tested and then promote use in the future.