Anaerobic Treatment Of Coal Gasification Wastewater And Strengthens By Hydrogen Enrichment

Coal gasification wastewater?CGW?generally contains high-concentration of toxic and refractory compounds,including phenols and nitrogen heterocyclic compounds.Due to the high toxicity of phenolic and nitrogen heterocyclic compounds,and great hazard to humans and environment,it is imperative to find an economical and efficient bioprocess.In this paper,the anaerobic treatment of CGW was studied.The effect of high concentration of quinoline and ammonia on the degradation of phenol was discussed.The feasibility of hydrogen enrichment to enhance the anaerobic degradation of phenol and quinoline was investigated,and the related mechanism was revealed.The UASB reactor operated steadily when the influent concentration of phenols was1000 mg L^-1 and the concentration of quinoline was between 100 to 600 mg L^-1.However,the specific methanogenic activity of the sludge was decreased gradually,while the substrate utilization rate of the sludge to phenol and quinoline was enhanced.It was found through the BMP tests that quinoline could be converted to methane while the conversion rate was less than 10%.The phenols and acetate co-metabolism hypothesis for quinoline degradation was discarded in our experiment,and the enrichment of quinoline-degrading bacteria was the prerequisites of the methane conversion of quinoline.Under methanogenic conditions,the degradation of quinoline was mainly via 3,4-dihydro-2?1H?-quinolinone and 8-hydroxycoumarin pathway,and the degradation of phenol was primarily via benzoate and cyclohexanone pathway.The genus Methanothrix substituting for Methanofollis became the dominant populations along the increasing concentrations of quinoline,and the relative abundance of genus Ornatilinea and Syntrophorhabdus were increased progressively at the expense of Syntrophus.When the concentration of quinoline was increased from 600 to 1200 mg L^-1 in the influent,the phenol utilization rate of the sludge was decreased by 60.5%.However,the degradation of phenol in the reactor was not affected.The increase of COD in the effluent mainly came from the accumulation of intermediate metabolites of quinoline.When the concentration of total ammonia nitrogen was 2 g L^-1,the degradation of phenol was not affected.But the degradation of phenol was severely inhibited as the total ammonia nitrogen concentration was over 4 g L^-1?the phenol removal rate was less than 8.4%?.Through the microbial analysis,high concentration of quinoline had the little effect on the archaeal community structure,but had a great modification on the bacterial community structure.Moreover,the inhibition on the degradation of phenol by ammonia nitrogen mainly came from the free ammonia nitrogen.Phenol produced stronger cumulative effects of toxicity on the microorganisms under high-concentration ammonia nitrogen,which further deteriorated the anaerobic degradation of phenol.Under the anaerobic condition,hydrogen enrichment had no promotion effect on the degradation of quinoline,but it could promote the degradation of phenol.Hydrogenotrophic methanogens had the strong tolerance ability of phenol than acetotrophic methanogens was found in our experiment.Hydrogen enrichment could alleviate the ammonia inhibition on the phenol degraders,and the alleviation effect was more obvious with the increase of hydrogen partial pressure.After the addition of hydrogen,phenol was rapidly converted to benzoic acid by the genus Syntrophorhabdus,and the relative abundance of Methanobacterium was also increased.Benzoic acid was further decomposed by Syntrophus and Syntrophorhabdus into hydrogen and acetate,which utilized by Methanothrix into methane finally.