Pathway And Kinetic Process Of Methanogenic From The Sludge Of Reclaimed Aquaculture Pools In The Subtropical Estuaries

The reclaimed aquaculture pools play an important role in offsetting carbonaceous greenhouse gas emissions in coastal areas.However,the mechanism of methane production of these aquaculture pools has not been clarified yet.Here,the anaerobic incubation experiments were carried out in the shrimp aquaculture(Penaeus vannamei)pools in the estuaries of main rivers in Fujian Province.On the one hand,CH₃F,isotope,and microbiological technologies were used to analyze the methane production pathway in aquaculture pools during the aquaculture and non-aquaculture periods in the estuary of Min river.On the other hand,models were used to observe kinetic process of methane prodcution in the sludge of three estuaries(Min river,Mulan river and Jiulong river)at the end of aquaculture period.Our results showed that:(i)In the research of CH₄production pathway,the potential methane production ranged between 3.40?13.76?g·g^–1,and the maximum methane production rates ranged between674 ng·g^–1·d^–1 and 84 ng·g^–1·d^–1.Among aceticlastic pathway were the dominant methanogenesis pathway during the breeding period in the Min river estuary.During the non-breeding period,the aceticlastic methanogenesis were only dominated in the aquaculture pools of Binfuzhou.Salinity and organic matter contents both can affect the methanogenesis pathway of the slurries in the aquaculture pools.The low-salinity aquaculture pools had a higher content of DOC and activities of BG and CBH,which could provide more substrates for aceticlastic methanogenesis.Nutrients also could affect methanogenesis pathway and improve the relative abundance of Methanomassiliicoccaceae and Methanofastidiosaceae.Methanosarcinaeae enriched in the nutrient-poor aquaculture pools.(ii)In the kinetic research of CH₄production,the methanogenesis process of the aquaculture pool'sludge can be divided into three stages:lag phase,production phase and stability phase.The lag phase occurred in the first 1?4 days,and the production period was mainly concentrated in 4?25 days.After 25 days,the methane accumulation curves in the aquaculture pools'sludge tended to be stable.Salinity and DOC,both can affect the kinetic fitting parameters of methanogenesis.With an increase in salinity,the potential methane production decreased from 5961 ng·g^–1 to 559 ng·g^–1,and the maximum methane production rates decreased from 674 ng·g^–1·d^–1 to 84 ng·g^–1·d^–1.Our results suggested that the first-order kinetic model and the modified Gompertz model are best fitted to the methane production process in low-and high-salt aquaculture pools,Combined,our results showed that salinity,organic matter and nutrient are important factors affecting the pathway of methanogenesis process.Offshore aquaculture aquaculture and the disposal of pool bottom sludge may greatly reduce greenhouse gas emissions.