Study On Anaerobic Co-digestion Of Waste Activated Sludge And Kitchen Waste Based On Magnetite

Waste activated sludge(WAS)in municipal sewage treatment plant and kitchen waste(KW)are important components of municipal solid waste.At present,the treatment of municipal solid waste mainly includes landfill,incineration,composting and anaerobic digestion(AD).Among them,AD is recognized as one of the best treatment techniques to reduce,harmless and resource-free solid organic waste,and has been widely used.However,due to the low C/N ratio of WAS,AD efficiency and methane production are always low,and the process is also unstable et.KW is mainly based on carbohydrates,the system is easy to be acidified in the case of AD alone,and the methane production process is unstable and so on.With the deepening of the research on AD,many researchers have pointed out that anaerobic co-digestion technology can make up for the shortcomings of single substrate digestion process,such as unbalanced nutrition(especially C/N),system acidification and so on,ensuring that the digestion process is stable and efficient.Considering that WAS and KW are relatively complex organic substances and the efficiency of hydrolytic acidification is low,it is necessary to pretreat them.However,the complicated pretreatment process often makes the treatment cost too high,which limits its engineering application.It is reported that magnetite can effectively enrich fe(III)reducing bacteria and mediate the direct interspecies electron transfer(DIET)between microorganisms,thus promoting the degradation of complex organic compounds.In this study,the mixed anaerobic co-digestion of WAS and KW was carried out,and the effects of different mixing ratios of WAS and KW on anaerobic digestion and methane production were investigated,to determine the optimal mixed feed ratio.On this basis,the effect of magnetite on AD and methane production was studied by adding magnetite to the co-digestion system,and exploring its promoting mechanism.The main findings are as follows:(1)The results of the anaerobic co-digestion of WAS and KW showed that the AD of KW alone could lead to the failure of the digestion process,and the AD of WAS only produced less gas and methane.When the anaerobic co-digestion of WAS and KW,the system was stable,and the production of biogas and methane was increased.According to the Gompertz equation,the mixed volatile solid(VS)ratio 4:12,2:14 and 1:15 of WAS and FW maximum methane production was 752 mL,699mL and 564 mL,which was 51.6%,63.1% and 22.3% higher than that of anaerobic digestion alone;the removal rate of VS was 39.4%,34.2% and 31.0% respectively,which was 39.7%,21.3% and 9.9% higher than that of anaerobic digestion alone.(2)The results of adding magnetite to the co-digestion system of WAS and KW showed that the addition of powder magnetite could promote the hydrolysis of complex organic substances such as protein and polysaccharide and increase the production of biogas and methane.In the 1:7 experiment group,the maximum methane production of 20 mesh,320 mesh and nano magnetite group was 784 mL,863mL and 924 mL,respectively,which was 7.2%,17.9% and 26.4% higher than that of no magnetite group.The results of microbiological analysis showed that,Clostridia and Methanothrix are enriched in the experimental group with magnetite addition.The abundance of Clostridia in the nomagnetite group,20-mesh,320 mesh and nano magnetite group was 10.5%,12.4%,24.2% and 26.5%,respectively;and the abundance of Methanothrix was 27.07%,32.19%,46.2% and 50.76%,respectively.It was speculated that magnetite mediates the DIET process between Clostridia and Methanothrix.