Effect Of Complex Effect Of Microplastics And Fat,Oil And Grease (FOG) In Anaerobic Co-digestion Of Sludge And FOG

Anaerobic co-digestion of sludge and FOG solved the problem of low C/N of sludge as a single substrate,greatly improves the degradation efficiency of sludge and methane production,and is a more efficient treatment method of sludge.In recent years,it has been found that microplastics(MPs)exist in large quantities in sludge and affect the anaerobic digestion of sludge.However,the effects of MPs on anaerobic co-digesting of sludge and FOG are rarely reported.In contrast to anaerobic digestion of sludge,the combined effect of FOG and MPs is likely to change the effect of MPs on anaerobic digestion system.Therefore,this study takes polyethylene(PE)and polyvinyl chloride(PVC)with high content in sludge as the representatives of MPs.By comparing the difference of the effects of MPs on anaerobic digestion of sludge and anaerobic co-digestion of sludge and FOG,the change of the effect of MPs on anaerobic system and its influence mechanism are explored when the combined effect of FOG and MPs exists.The effect of PE MPs with particle size of 300μm on methane production of anaerobic co-digestion of sludge and FOG was investigated.The results showed that when sludge was used as a single substrate,the methane production of S-50(50 particles /g TS)and S-200(200particles /g TS)was enhanced 37.9% and 16.4%,respectively,compared with S-control.When sludge and FOG were used as co-substrate,the methane lifting rate of C-50 and C-200 compared with C-control was lower than that of S-50 and S-200 compared with S-control,indicating that the presence of FOG would weaken the promoting effect of PE on methane generation.The main reason is that there is a compound effect between FOG and MPs,which weakens the function of MPs as biological carriers and thus weakens the catalytic effect of PE on methanogenesis.The abundance of JGI-0000079-D21 bacteria in the anaerobic digestion of sludge group was higher than that in the anaerobic co-digestion group containing the same amount of PE,which may lead to the reduction of methanogenesis effect in the anaerobic co-digestion group.With PVC as the representative MPs,R50-50(50μm,50 particles /g TS)PVC with the highest methane yield and R300-200(300μm,200 particles /g TS)PVC with the lowest methane yield in sludge anaerobic digestion experimental group were selected to explore their effects on the methane production of the anaerobic co-digestion of sludge and FOG.The results showed that the presence of FOG in anaerobic co-digestion reduced the positive effect of PVC with a concentration of 200 particles /g TS and a particle size of 300μm on methane production,and also reduced the inhibitory effect of PVC with a concentration of 50 particles/g TS and a particle size of 50μm on methane production.The main reason may be that the combined effects of EPS component content,the carrier effect and toxicity affect of PVC effected the methane production of each group.The distribution of archaea community in the anaerobic digestion sludge group was more dispersed than that in the anaerobic co-digestion group,indicating that the addition of PVC had greater effect on the methane production of the anaerobic digestion of sludge than that of the anaerobic co-digestion of sludge and FOG.In this study,the effects of PE and PVC on methane production by the anaerobic digestion of sludge and anaerobic co-digestion of sludge and FOG were investigated,which provided a preliminary understanding of the changes in the effects of MPs on anaerobic system in the presence of FOG and the mechanism of action.