Study On The Degradation Characteristics And Mechanism Of Propionic Acid In The Enhanced Anaerobic Digestion System Of Redox Mediators

Propionate is very easily produced,but it is difficult to eliminate them during the anaerobic fermentation process of organic matter.Therefore,propionate is usually accumulated in an anaerobic digestion system,causing the pH decrease.It leads to the "acidification" of the system and the failure of the anaerobic biological treatment process.Redox mediators can use their electron transfer function to improved anaerobic degradation of organic pollutants.Therefore,this study investigated that the effect of redox mediators on the anaerobic degradation of propionate,by using propionate as the sole carbon source and the granular sludge in the upflow sludge bed anaerobic reactor(USAB)of the paper mill as the inoculation sludge.In addition,the succession characteristics of microbial communities was analyzed by high-throughput sequencing.In this study,anthraquinone-2,6-disulfonic acid(AQDS),graphene oxide(GO)and humic acid are selected as redox mediators to enhance the anaerobic degradation of propionate.The results showed that AQDS inhibited propionate degradation,while graphene oxide and humic acid can promote the propionate degradation.Under the condition of a humic acid concentration of 50 mg/L,both the propionate removal and the cumulative methane production reached the maximum.They were 98% and 97.2 m L,respectively.Microbial community structure analysis showed that 50 mg/L humic acid made the dominant comunity in the anaerobic sludge from Longilinea,Acinetobacter,Pelolinea,and Petrimonas in control to Longilinea and Petrimonas.The effects of different pH on the humic acid-mediated anaerobic degradation of propionate showed that the propionate removal and the cumulative methane production were the highest at pH 7.0,which were97.7% and 117.8 m L,respectively.Microbial community structure revealed that,Petrimonas was the dominant genus in the original sludge.Under the pH was 5.0 and 6.0 conditons,Petrimonas,Longilinea and Subdivision3＿genera＿incertae＿sedis became the dominant genus.In addition,when the pH was 7.0 and 8.0,Longilinea became the dominant genus.Propionate degradation was significantly inhibited at pH 4.0-4.5.The effect of reduced iron powder on humic acid-mediated propionate showed that propionate removal and the cumulative methane production showed a trend of first increasing and then decreasing at reduced iron powder concentration of 0-15 g/L.When the reduced iron powder was 4 g/L,propionate removal and the cumulative methane production reached the maximum,which were 97.7% and 100 mL,respectively.Microbial community structure revealed that Petrimonas was the first dominant genus in the original sludge.The dominant genus succeeded as Longilinea when propionate was used as sole carbon source.When the reduced iron powder concentration was 2 g/L,4 g/L,6 g/L,and 15 g/L,the dominant genus were Acinetobacter,Romboutsia,Longilinea and Longilinea,respectively.The relative abundance of Romboutsia in 4 g/L reduced iron system was 9.4%.