Study On Organic Components Transformation And Microbial Community Structure Of Coking Wastewater Treatment Processes

Coking wastewater is a typical refractory organic wastewater,whose treatments include pretreatment,biological treatment and advanced treatment.Biological treatment can degrade most of organic matters in coking wastewater,which is the core unit of the whole process.According to previous studies at home and abroad,the common biological technologies are A²/O and A²/O² processes.At present,the research on A²/O and A²/O²processes mainly focuses on COD,ammonia nitrogen,phenol,a single organic substance,or is limited to research in the laboratory.Few studies have delved into the migration and transformation of organic matters in various biological units,microbial community structure,and the relationship between the degradation of organic matter and the microbial community structure in coking wastewater.The refractory organics are the main cause of high COD in coking wastewater.The degradation of organics mainly depends on the microbial community structure in the wastewater,which affects the reaction mechanism and process optimization of the biological treatment process.Therefore,it is necessary to study the influence of A²/O and A²/O² processes in the degradation of organic matter in coking wastewater,the change of microbial community structure,and the relationship between them.In this study,the A²/O and A²/O² processes in the actual coking plant were chosen as the main technology.The effluent quality of the two processes was compared.The degradation of organics in two processes was also examined.The diversity of microbial community structure using high-through put sequencingwas analyzed,and the relationship between refractory organics and microbial community structure was explored.The results above provide theoretical basis for the stable operation of the biological treatment technology of coking wastewater.The main conclusions of this study are as follows:1)The removal rate of A²/O² process to chromaticity,COD,UV₂₅₄54 and NH₄⁺-N were23.1%,96.6%,95.1%and 99.1%,respectively.It was higher than the removal efficiency of A²/O process.It showed that the removal efficiency of A²/O² for coking wastewater was better.The removal of organics by A²/O process was mainly concentrated in the aerobic plant unit,while A²/O² process was in anoxic unit.The aerobic unit has a significant removal effect on organics,due to the hydraulic retention time（HRT）of anoxic tank in A²/O² process is 1.4 times that of A²/O process.The water quality of the A²/O² process is better than that of the A²/O process.In the anoxic unit,the removal rate of TN in A²/O and A²/O² process is 30.2%and 87.4%,respectively,and the decrease rate of NH₄⁺-N is 30.3%and 77%respectively.After A²/O and A²/O² process,NH₄⁺-N removal of 48.82mg/L and34.70 mg/L,NO₂-N concentration increased by 0.10 mg/L and 0.04 mg/L respectively,indicating the simultaneous nitrification and denitrification reaction in oxygen and aerobic units.The A²/O process aeration tank in the coking plant has good sedimentation performance and high concentration.The A²/O² process MLVSS/MLSS is larger,and the indirect reaction sludge activity is higher.2)Coking wastewater mainly contains phenolic compounds,PAH,and heterocyclic compounds containing N,O,and S,which are the main causes of high COD in coking wastewater.After the biodegraded by A²/O and A²/O² processes,the effluent mainly contained refractory organics including N,O,S heterocyclic compounds,PAHs,alcohol compounds,and carboxylic acid compounds,.The degradation of organics by the A²/O process is mainly in the aerobic biological treatment unit,and the degradation of phenolic by A²/O² process begins to significant in the anaerobic unit.3D-EEM and GC/MS were used to analyze the organic matter in coking waste water.The method of GC/MS has the merit of visual analyzing a certain substance.However,the operation steps are complex and the cost is expensive.By contrast,the method of 3D-EEM can not visually observe a certain organism,but it can be refined to a small class or even to a certain substance by the FRI（fluorescence regional integration）method,and it has the advantages of simplicity,rapidity accuracy and cheapness.Therefore,3D-EEM can be used as a common and rapid measurement method for the analysis of organic matter in water bodies.3)Firmicutes were the most abundant in anaerobic sludge or the A²/O and A²/O² processes,and the dominant culture for anoxic sludge,aerobic sludge,and contact oxidation sludge were Proteobacteria.In A²/O and A²/O² processes,Clostridia dominated in anaerobic sludge,Betaproteobacteria dominated in anoxic sludge and aerobic sludge,and Alphaproteobacteria dominated in contact oxidation sludge.A²/O and A²/O² processes were anaerobic sludge and anoxic contamination.The dominant bacteria of anaerobic,anoxic and aerobic sludge were Thermoanaerobacter,Woodsholea,Thiobacillus,respectively.The dominant genus of A²/O² contact oxidation sludge was Halomonas.Therefore,the effects of environmental conditions（temperature,dissolved oxygen,etc.）on community structure are greater than the process factor.The degradation of refractory organics in water mainly depends on the combination of dominant microorganisms and diverse microorganisms.The core species for degradation of organic matter such as phenol,quinoline,and quinone may be Thermoanaerobacter,Woodsholea,Thiobacillus,Halomonas,Pseudomonas,Thauera,and Thauera.