Enhancement Of Granular Activated Carbon On Methanogenic Degradation Of Propionate

The degradation of volatile fatty acids（VFAs）such as propionate and butyrate generated by the fermentation bacteria in anaerobic digestion process should be convert to acetate and H₂/CO₂ first.Finally,acetate and H₂/CO₂ convert to CH₄ by methanogens.It has the obvious characteristic of syntrophic degradation from VFAs to CH₄.In addition,propionate is deemed to an important factor of the effect and operation stability because of its easy-generation and hard-degradaton in anaerobic digestion system.Based on the understanding that granular activated carbon（GAC）can promote the interspecies direct electron transfer（DIET）process of syntrophic VFAs methanogenesis,this study based on the start-up operation of anaerobic sequence batch reactor（AnSBR）,the enhancement efficiency of GAC on the process of propionate degradation and methane production was studied.The regulation effect of GAC on the process of propionate degradation and methane production under the stress of key factors such as hydrogen pressure,p H and propionate concentration were discussed.The regulation and enhancement of GAC were analyzed from the perspective of microbial community structure.The results showed that in AnSBR reactor with propionate as the only carbon source,20 g/L GAC was conducive to increase the biomass which supported the rapid start-up time and higher methane production.During long term operation,the prompting effect of GAC became weakly and the methane production of the two AnSBRs tended to be the same,indicated that the enhancement of GAC was a short-term effect.Microbial community structure analysis and SEM results revealed that the microbes on GAC surface showed higher community richness and diver sity.had been enriched to 3.2%～10.4%on GAC surface,which allowed propionate could be degraded by disproportionation pathway.The mathanogens such as Methanothrix and Methanosarcina were attached to bacteria Smithella on the surface of GAC,indicated that DIET pathway was likely to be established on the surface of GAC.The effect of GAC on the methane-producing process of propionate degradation under stress condition was investigated.The results showed that in high hydrogen pressure condition（15 k Pa）,the system with the GAC addition could degraded propionate without inhibition and the system without GAC was significantly inhibited at the beginning in contrast.In addition,it was found that the disproportionation metabolism pathway to degrade propionate was promoted.Adding GAC could alleviate the inhibition under weak acid p H stress（6.0～6.5）,but still been inhibited at low p H condition（≤5.5）.Under the stress of propionate concentration（≥2500 mg/L）,the degradation rate of propionate with GAC was greatly improved.