The Combination Of Potassium Ferrate Treatment And Microbial Electrolytic Cell Enhance The Degradation Of Human Feces

There are many problems in rural toilets in China,such as poor sanitary conditions,biodegradation of excreta and low utilization of resources.Therefore,the safe and harmless disposal of human excreta has become an urgent problem to be solved in rural toilets.Microbial electrolytic cell(MEC)has a higher biodegradation rate and energy recovery rate than conventional anaerobic digestion(AD).In this study,potassium ferrate was used for pretreatment of feces.Through the influence of different concentrations of potassium ferrate on substrates,the group with the best treatment effect was selected as the substrate of the subsequent potassium ferrate conditions in the experimental group.Through the analysis of the orthogonal combination with different voltage condition,waste treatment effect under different conditions,the feasibility of its application in waste treatment,advantages and actual operational provide certain data support,offer some help for broadening the waste treatment technology,to look forward to the follow-up to the waste reduction and recycling to provide guidance and reference significance.Human feces were taken as the research object in this paper.First,feces were pretreated with potassium ferrate at concentrations of 0.3,0.6,0.9 and 1.2 g/g feces VS to study the effects of different concentrations of potassium ferrate on substrate release.It was found that potassium ferrate was an effective treatment agent for fecal pretreatment.The concentration of potassium ferrate was below 1.2 g/g VS,showing a positive correlation to the efficacy of fecal pretreatment.After 2 h treatment,the concentrations of total carbon,total nitrogen,polysaccharide and protein in the liquid phase were greatly increased.Compared with the control group,the indicators of 1.2g/g VS group with the best performance increased by 73.67%,66.57%,34.7% and149%.The pretreatment and different voltages(0 V,0.8 V and 1.2 V)were used as the control conditions to strengthen the anaerobic digestion system(MEC-AD)in microbial electrolytic cell after the concentration of pretreatment agents was selected to optimize the process parameters.We found that the peak methane-producing efficiency of each unpretreated group was 0.111 m L/(m L·d),0.092 m L/(m L·d)and0.132 m L/(m L·d).Methane production in the unpretreated groups was 184.45 m L,242.28 m L and 206.82 m L,which were increased by 31.35% and 12.13% in 0.8V and1.2V groups,respectively.At this time,we found that although the 1.2V treatment group had a higher degradation efficiency,its methane production rate was not as good as that of the 0.8V treatment group.In addition,potassium ferrate has a significant effect on the biodegradation and reduction of feces,and it has a strong degradation effect on macromolecular organic matter,which is conducive to the dissolution of organic matter and the reduction of ORP in the system.Compared with the control group,the methane production was also significantly increased.The methane production rates of the pretreatment groups were 0.101 m L/(m L·d),0.161 m L/(m L·d)and 0.134 m L/(m L·d),and the methane production was 223.12 m L,325.13 m L and 276.82 m L,respectively.It increased by 20.97%,34.20% and 33.85%compared with the control group.Bacteroidetes,Firmicutes and Proteobacteria were the dominant bacteria in each sample,occupying more than 94.8% of each treatment group.Among them,Bacteroidetes and Proteobacteria in different voltages have the abundance of 0.8V >1.2V >0 V.This indicates that the applied voltage group has a better degradation rate and electrochemical activity,which makes it have a better gas production efficiency.In addition,in terms of microbial community structure,potassium ferrate group showed differences in microbial community.Potassium ferrate group could reduce Bacteroidetes in the community,and 0 V,0.8 V and 1.2 V groups decreased by 14.5%,32.9% and 33.6%,respectively.However,the relative abundance of Proteobacteria electricity-producing bacteria increased.Each group increased by 85.2%,150.2%,and88.6%,respectively.This makes the microorganism have higher electrochemical activity under the condition that the number of degrading bacteria is roughly unchanged,which makes it have better degradation rate and gas production efficiency.