Effect Of Sulfidated Zero Valent Iron On The Biogas Production And Microbial Community During The Anaerobic Co-digestion Of Waste Activated Sludge And Food Waste

Anaerobic digestion（AD）technology can simultaneously realize the reduction,resource utilization and harmlessness of organic solid waste so it is an ideal method to treat organic solid waste such as food waste（FW）and waste activated sludge（WAS）.However,in practical,the treatment efficiency and energy yield of AD often fail to reach the theoretical value.As a result,many strategies such as pretreatment,anaerobic co-digestion（Aco D）of different substrates,and introduction of exogenous additives have been used to improve the effect of AD.In this study,sulfidated zero valent iron（SZVI）was obtained by sulfidation of zero valent iron（ZVI）,which was used as an exogenous additive to enhance the Aco D of FW and WAS.The effects of different doses of SZVI on the different stages of Aco D were explored.And the changes of microbial community structure and composition during Aco D were analyzed by 16S r RNA high-throughput sequencing technology.The main conclusions are as follows:（1）The specific surface area analysis and X-ray photoelectron spectroscopy characterization of SZVI proved that S was successfully loaded on the surface of ZVI,and its specific surface area,pore volume and pore diameter were larger than that of ordinary ZVI,and its properties were superior.Sequential batch experiments show that the change of Fe/S molar ratio affected the promotion of SZVI on the methane production of Aco D.When the Fe/S molar ratio was in the range of 20 to 50,the promotion effect of SZVI on Aco D increased as the degree of sulfidation increased.But when the degree of sulfidation further increased and the Fe/S molar ratio reached10,the promotion effect of SZVI on Aco D became weaker.The reason may be that higher S content causes the formation of a thicker Fe S_x layer on the surface of ZVI,which prevents the internal Fe⁰ from contacting the outside,inhibits the corrosion and hydrogen production reaction of SZVI,and thus reduces its promoting effect on AD.（2）The influence of SZVI on the different stages of Aco D showed that the addition of SZVI had no obvious effect on the solution,hydrolysis and acidification stages of Aco D.A rapid increase in the concentration of soluble proteins,carbohydrates or volatile fatty acids（VFAs）was not observed,by contraries the consumption rate of VFAs increased.Meanwhile the addition of SZVI had a significant effect on the methanogenic stage of Aco D and drastically improved the production of methane and the utilization of substrates.When the dosage of SZVI was10 g/L,the accumulative methane production was 264.78 m LCH4/g-VS,which was33.18%higher than of the Blank group（198.81 m LCH₄/g-VS）.In addition,the accumulative methane production at ZVI dosage 10 g/L was 238.68 m LCH₄/g-VS,which was not only lower than that of group at same SZVI dose,but also slightly lower than that of group at SZVI dosage 6 g/L（242.88 m LCH₄/g-VS）.Obviously,the promotion effect of SZVI on methane production in Aco D of FW and WAS was better than that of ordinary ZVI.（3）Microbial analysis showed that the addition of SZVI had a significant influence on the microbial community,which reduced the microbial diversity and promoted the growth and reproduction of some microorganisms.Among them,the microbial community structure and composition in the group added with 10g/L SZVI exhibited the biggest difference compared with the Inoculum and Blank group.Further analysis showed that the addition of SZVI significantly increased the abundance of multifunctional methanogens and hydrogenotrophic methanogens,but had no significant effect on acetoclastic methanogens.Moreover,at the same dosage,the effect of SZVI on the microbial community was more obvious than that of ordinary ZVI.（4）The analysis of direct interspecies electron transfer（DIET）and electron transport system（ETS）activity showed that the addition of SZVI promoted the growth and reproduction of microorganisms that could participate in DIET such as Methanobacterium,Methanosarcina and Syntrophomonas.Their relative abundance in the group added with 10 g/L SZVI were 7.22%,14.57%,and 6.80%,respectively,which were much higher than the 3.33%,12.25%and 4.19%in Blank group.The ETS activity of the system also showed a similar trend.After the Aco D,the ETS activity was as high as 24.26 INTF/（g-TS·h）,which was 1.83 times higher than that of the Blank group.