Study On Promoting Effect And Mechanism Of Divalent Iron Cobalt Nickel Chloride On Fermentation Of Cassava

The cassava vinasse wastewater has a high-concentration COD and heavy metals so that inefficient treatments will cause serious pollution to the environment.Therefore,an efficient and cost-friendly treatment method was urgently needed.In this paper,the anaerobic fermentation of cassava vinasse grains was studied and it could not only reduce the pollution degree of wastewater to the environment,but also produce clean energy—biogas.The process of anaerobic fermentation of cassava vinasses to produce biogas is affected by factors such as temperatures,pH,hydraulic retention time,and different concentrations and spiciations of trace metal elements.Trace metal elements are essential for the activity of some methanogenic enzymes and suitable trace metal concentrations can effectively promote biogas production.In this paper,the effects of temperatures of cassava vinasse’s waste fermentation,single addition of trace metal elements（iron,cobalt,and nickel）,and optimum mixture ratio on biogas production were studied.Besides,the relevant conclusions have been applied to industrial pilots.The main research contents and results are summarized as follows:1)By setting two variables of thernophilic（55°C）and mesophilic（35°C）,it is found that thernophilic conditions have stronger degradation ability to volatile fatty acids produced during fermentation,and it is more conducive to stable the operations of biogas production.Under thernophilic conditions,the dehydrogenase activity is stronger and the COD removal is also increased by 20%.Also,the total biogas production in the fermenter is almost three times of the biogass production under mesophilic condition,reaching 23.33 L.2)By studying the effects of single iron,cobalt,and nickel on biogas production,COD removal rates,VS removal rates,and dehydrogenase activity.It is found that iron,cobalt and nickel can promote enzymes’activitiy and lead to the improvements of biogas production at50 mg·L^-1,1 mg·L^-1 and 5 mg·L^-1,respectively;and the maximum COD removal at 100mg·L^-1,1 mg·L^-1,and 5 mg·L^-1·,respectively.When exploring the synergistic effect of mixed salt in the same reactor,five groups of different mixing ratio groups of iron,cobalt,and nickel were designed and studied.Compared with the control group,when Fe²⁺:Co²⁺:Ni²⁺=100mg·L^-1:1 mg·L^-1:5 mg·L^-1,biogas production was increased 53.71%.At the same time,COD removal,VS removal,and dehydrogenase activity were also obviously enhanced.3)High-throughput sequencing revealed the mechanism of mixed salt on biogas production:through Alpha diversity and Beta diversity analysis,it was proved that mixed salts can enhance the species diversity of anaerobic microbial communities.The Simpson index for measuring microbial diversity is positively correlated with the gas production in the reaction tank.Moreover,by analyzing the abundance of the species of the bacterial community and the abundance of the species,Firmicutes is the dominant species in each fermenter,Defluviitaleaceae,and Hydrogenophilaceae.The decrease in the number of other species and the increase in the species of Porphyromonadaceae and Petrotogaceae indicate that the metabolic type of the microbial community changed from methanogenesis to acid production at the end of the reaction.4)Based on the results obtained from laboratory research,an industrial pilot test was conducted in the vinasse’s wastewater treatment section of a chemical plant in Lianyungang,and the IBioBooster（IBB）system was used to ferment methane in bio-enhanced IC tanks.The results of the pilot test showed that the IBB system could effectively increase the microbial concentration and the activity of anaerobic microorganisms;the two 1 m³ IBB systems successfully increased the biogas production and methane concentration of the 5000m³ IC tank.Through economic and technical accounting,IBB biofortification can create an economic value of 1200 to 1600 RMB/day by increasing methane production.