Effect Of Nano Ferroferric Oxide On Anaerobic Digestion Of Sludge

Anaerobic digestion of sludge is a reliable technology used worldwide tostabilize organic matter,reduce solids,destroy pathogens,and produce biogas as an energy source.As a complex biological process,anaerobic digestion converts the residual sludge by hydrolysis and digestion.Due to the advantages of anaerobic digestion,many studies have begun to find ways to optimize the anaerobic digestion of sludge,such as co-digestion and adding chemicals,etc.Large studies have shown that nanoparticles play an important role in anaerobic digestion.In this study,the effect of Fe₃O₄ NPs on anaerobic digestion was studied,different concentrations of Fe₃O₄ NPs on the changes of the organic matter such as protein,polysaccharide,VFAs and degradation products,gas production and gas components,enzymes and microorganisms in anaerobic digestion were investigated.The kinetic model of the anaerobic digestion process was studied,and try to use a method of electrochemical to explore the process of anaerobic digestion,so as to provide a theoretical basis for improving the anaerobic gas production process.Research indicates:?1?Different concentrations of Fe₃O₄ NPs had different effects on anaerobic digestion gas production of residual sludge.The results showed that the group of200mg/L Fe₃O₄ NPs had the highest cumulative gas production,reaching 809 N mL g^-1 VS.With the increase of Fe₃O₄ NPs concentration,when the concentration reached600mg/L,it inhibited the gas production.Further analysis of the gas composition revealed that the 200mg/L Fe₃O₄ NPs experimental group had the highest methane content,which was above 90%,while the 600mg/L Fe₃O₄ NPs experimental group had the lowest methane content only about 20%,which inhibited the generation of CH₄.?2?The Logistic model,the modified Gompertz model and the BPK model were used to fit the anaerobic digestion gas production.The results showed that the BPK model cannot fit the regular of the anaerobic digestion biogas change,for the Logistic model and the modified Gompertz model,the effect of Fe₃O₄ NPs on the anaerobic digestion gas production changes in line with the rule.The modified Gompertz model had the best fit,with a maximum R² of 0.99.?3?Different concentrations of Fe₃O₄ NPs had different effects on the changes of organic matter in anaerobic digestion.The results showed that the experimental group of 200mg/L Fe₃O₄ NPs had the highest degradation rates of proteins and polysaccharides,and the highest TCOD degradation rate was 94.9%,which was beneficial to the degradation of organic matter.With the increase of Fe₃O₄ NPs concentration,the degradation rate of organic matter was inhibited,and the degradation rate of TCOD decreased to 90.9%.The VFAs reached the highest in the 200mg/L Fe₃O₄NPs experimental group,in which the acetic acid concentration was as high as 693mg/L.When the concentration of Fe₃O₄ NPs reached 600mg/L,the formation of acetic acid was inhibited and was 14.1%lower than that in the blank group,which destroyed the acid-base balance in the system,caused the ammonia nitrogen concentration up to779mL,and the pH was 8.1,inhibited methanogen activity and CH₄ production.?4?Different concentrations of Fe₃O₄ NPs had different effects on enzymes and microorganisms in the anaerobic digestion.The addition of Fe₃O₄ NPs was conducive to improving the activity of proteases,in 200mg/L Fe₃O₄ NPs experimental group was the highest,which was 3.8 times of the blank group.For dehydrogenases and acetate kinase,the activity of dehydrogenases and acetate kinase in the 200mg/L Fe₃O₄ NPs experimental group reached the maximum.With the increase of Fe₃O₄ NPs concentration,the activity of enzyme decreased.On the contrary,because iron ions participate the production of coenzyme f₄₂₀,the coenzyme f₄₂₀ could reach a maximum of 1.8Umol/g VSS when the Fe₃O₄ NPs concentration was 600mg/L.The changes of bacteria and archaea were also different.According to the high-throughput sequencing,the Longilinea and Ornatilinea in the experimental group of 200mg/L Fe₃O₄ NPs were relatively high,accounted for 8.8%and 4.1%,and facilitates the production of Methanothrix,which made Methanothrix up to 69%,while the 600mg/L Fe₃O₄ NPs experimental group had the lowest abundance of Methanothrix,inhibiting the growth and reproduction of methanogens.?5?This study attempts to explore the anaerobic digestion process by electrochemical method.The results showed that compared with graphite electrodes,the modified Fe₃O₄ NPs electrode had a higher current signal,up to 0.022mC.The addition of Fe₃O₄ NPs was beneficial to improve the electrochemical activity of the electrode.Enzyme and microbial electrode results showed that under the protein and acetic acid electrolytes,the 200mg/L Fe₃O₄ NPs experimental group enzyme electrode produced the highest electricity,0.004mC and 0.007mC,respectively.As the concentration of Fe₃O₄ NPs increased,the electricity gradually decreased.For the microbial electrode,the electricity produced by the 200mg/L Fe₃O₄ NPs experimental group was the highest,while the electricity of the blank group started to increase in the later stage,and was higher than the 600mg/L Fe₃O₄ NPs experimental group.In summary,the electrochemical method could react the changes of enzymes and microorganisms more quickly.