Study On Biodegradation Of Refractory Organic Compounds In Coking Wastewater By Redox

The coking industry is a pillar industry and a heavy polluting industry in Shanxi Province.Coking wastewater is industrial wastewater which contain polycyclic aromatic hydrocarbons(PAHs).PAHs are typical persistent organic pollutants.The nature of persistent,highly toxic and rich makes them become one of organic materials which most difficult to degrade in coking wastewater.It also becomes a major component of the toxic residue of the effluent.Redox mediators(ROMs)can accelerate the transfer of electrons between electron donors and electron acceptors through the cyclic conversion of their own oxidation state and reduction state,which can increase the biological redox reactions rate of one to several orders of magnitude.So it can promote anaerobic bioconversion of refractory organic pollutants.In this study,the electron transfer function and biocatalysis function of ROMs are used to accelerate the transfer of electrons from PAHs to ROMs,resulting in promoting anaerobic biodegradation of PAHs and enhancing the advanced treatment of coking wastewater.In this study,high-throughput sequencing technology was first used to analyze the composition of activated sludge in anaerobic,anoxic and aerobic tanks of coking wastewater treatment plants.The results showed that Halostagnicola and Natronorubrum are the dominant bacteria in anaerobic tanks.Methanosaeta,Thermogymnomonas,Methanosphaerula,and Methanosarcina are dominant methanogenic archaea.The functional bacteria in the anoxic tank are Thiobacillus and Thauera.There are also functional bacteria such as Sphingomonas,Novosphingobium and Georgfuchsia,which can degrade polycyclic aromatic hydrocarbons(PAHs)in the anoxic tank.The functional microorganisms in the aerobic tank are Rhodocyclaceae,Phycisphaera and Nitrospira.Then activated sludge in anoxic tank was acclimated and enriched with PAHs as the only carbon source.Then,the ecological succession of PAHs-enriched cultures was analysed during the enrichment process.There was a significant succession of the microbial composition before and after enrichment.After the fifth generation of enrichment,the dominant functional microorganism was Thauera,and the functional diversity of degrading PAHs increased significantly after the tenth generation.There are Sphingomonas,Novosphingobium,and Georgfuchsia except Thauera.On this basis,the effectiveness of anaerobic biodegradation and its influencing factors of ROMS-enhanced PAHs were studied using enriched cultures as seed sludge.The results showed that AQDS,AQS,and humic acid have a certain role in promoting the degradation of PAHs.Among them,AQDS has the most significant enhancement effect,while humic acid is the weakest,and when the concentration of AQDS is 0.5 mmol/L,strengthening effect is the best.Nitrate promotes anaerobic biodegradation of PAHs by mediators,and also promotes denitrification of anaerobic biodegradation system.Finally,two strains of PAHs degrading bacteria SXU-1 and SXU-2 were isolated from the enriched cultures,which were 99% and 99% similar to Georgfuchsia and Sphingomonas respectively.Both Georgfuchsia and Sphingomonas have the ability to anaerobicly degrade PAHs.Through study on glutathione S-transferase activity of SXU-2 strains by mediator-mediated,it was found that mediator-mediated anaerobic biodegradation of PAHs can enhance the expression of GST,thereby increasing the tolerance to toxicity and electron transfer effectiveness of microorganisms.