Study On Process Characteristics Of Treating Simulated Coking Wastewater Using A Step-feed Multiple Hybrid A/O Biological Aerated Biofilter

Coking wastewater is a typical industrial wastewater with the characteristic of high COD,high ammonia nitrogen and non-biodegradation.It mainly contains high concentration phenol and a large number of nitrogen-containing heterocyclic organic compounds such as pyridine,quinoline and indole.It is the difficulty and key to achieve high efficiency removal of refractory organics and nitrogen that meet the standard of biochemical effluent.However,it is extremely difficult for traditional single point influent and one-stage anoxic/aerobic(A/O)activated sludge process to achieve the goal of the removal of refractory organic matter and nitrogen.Therefore,a new technology of Step-feed Multiple Hybrid Anoxic/Oxic Biological Aerated Filter(SMHA/OBAF)is proposed in this study.The step-feed can ensure the reasonable distribution of organic matter load and the balanced utilization of carbon source in different stages.The multi-stage A/O and biological aerated filter are combined organically by utilizing the formed anoxic and aerobic areas due to the natural separation of BAF intermediate aeration,which can provide carbon source for denitrifying bacteria in the anoxic area,and the remaining organics are further removed in the aerobic area.The multi-stage A/O can forcefully ensure the high efficiency of nitrification and denitrification,so as to realize the simultaneous removal of refractory organics and nitrogen in coking wastewater.The small scale SMHA/OBAF system with three-stage A/O is adopted to treat simulated coking wastewater in this study,in which phenol was used as the main substrate and pyridine,quinoline and indole with different concentrations and proportions were added to reflect the water quality characteristics of the actual coking wastewater,In the long-term operation and different influent conditions,the emphasis was to investigate the removal characteristics of COD,phenol,pyridine,quinoline,indole and TN,and studied the spectroscopic characteristics of each section of effluent.The organic components of influent and effluent were identified and analyzed.The microbial community diversity and community structure composition of each section in the process were analyzed,with the focus on the functional characteristics of key bacteria groups to determine the contribution of COD and TN in each section.Finally,the removal kinetics of COD and TN in the system was analyzed.The research results will provide the theoretical basis and technical parameters for the effective treatment of refractory organic pollutants and nitrogen in the actual coking wastewater by the SMHA/OBAF process.The main conclusions of this study are as follows:(1)The removal performance of COD,phenol,pyridine,quinoline and indole under different operating conditions was investigated.The results showed that when HRT was extended to 48h appropriately with the influent COD loads of 1.993 kg/m^3.d(4100 mg/L)and ammonia loads of 0.072 kg/m³d(150 mg/L),the removal rates of COD,phenol,pyridine,quinoline and indole are all as high as 99.9%with the optimal removal effect.Simultaneously,it was found that most of phenol and indole were degraded and utilized in the anoxic zone,while the removal contribution rates of pyridine and quinoline were(21.66%,32.58%)and(22.79%,25.89%)in the A2 and A3 zone,which was higher than that in the corresponding aerobic zone.EPS analysis of biofilm suggested that the polysaccharide content in anoxic areas was significantly higher than that in aerobic area,while the protein content was significantly lower than that in aerobic area.These findings were closely related to the treatment efficiency of the system.(2)The spectral analysis of effluent in each section was carried out.The UV-vis spectrum showed that the aromaticity,molecular weight and polymerization degree of the wastewater decreased obviously after the treatment in the anoxic and aerobic areas.FTIR spectrum indicated that a large number of amide organic compounds with C=C and C=O double bonds,a small amount of polysaccharides and alcohols with C-O,and the intermediate products of phenol were produced after the treatment of A1 zone.From the anoxic area to the aerobic area,the intensity and quantity of absorption peak decreased evidently.3D-EEM spectrum manifested that there were a lot of aromatic protein organics,soluble microbial byproducts and marine humic acids in the anoxic area affected by the raw water.After aerobic treatment,only a small amount of aromatic protein organics remained with decendent fluorescence intensity.The results of GC-MS analysis demonstrated that after the SMHA/OBAF treatment of phenol,pyridine,quinoline and indole in the raw water,only a small amount of phenol and some small alcohols,alkane alkenes,benzene series,ketones,esters and other organic compounds were found in the effluent.(3)The influence of different factors on the denitrification performance of the system was discussed.The TN removal capacity was improved by adjusting the water quality parameters and operation parameters.The results showed that the TN removal rate will increase slightly with the increase of COD and ammonia nitrogen load,while the decrease of COD load and the increase of p H value will obviously increase TN removal performance from 69.3%to 98%.The analysis of the three nitrogen concentration along the way suggested that there existed simultaneous nitrification and denitrification(SND)effect in O2 and O3area.The removal contribution rate of TN in A3 area was the highest(25.9%),followed by O2(24.4%)and O3(19.2%).(4)High throughput sequencing found that the influent COD load and organic composition were the main factors affecting the microbial community richness and diversity.At genus level,the dominant bacteria of A1 and A2 was methanthrix,while the dominant bacteria of A3 was gemmobacter.There were a lot of phenol degrading bacteria,heterocyclic degrading bacteria,methanogenic bacteria,acidogenic bacteria and denitrifying bacteria in the system.The dominant bacteria of O1,O2 and O3 were ferruginibacter(2.78%),dokdonella(8.39%)and Bacillus(20.18%).Nitrosomonas is the main AOB,accounting for0.39%,0.32%and 0.05%of the AOB.However,NOB was not detected,which indicated that short cut nitrification takes place in the system.A large number of heterotrophic nitrifying-aerobic denitrifying bacteria,such as bacillus,rhizoctonia,pseudomonas and nitrogen fixing bacteria,were found,accounting for 4.53%,3.59%and 2.99%of each section,respectively.In addition,the anammox bacterium Candidatus kuenenia was also detected in three aerobic areas.The above functional microorganism discovery showed that the A1 area was dominated by organic matter acidification and methane production.A2 area was mainly methane producing,with denitrification and organic matter degradation.Denitrification was the main processes in A3 area.In O1 and O2zones,heterotrophic nitrification aerobic denitrification and shortcut nitrification anaerobic ammonia oxidation are the main processes,while in O3 zone,heterotrophic nitrification aerobic denitrification was the main processes.(5)Biochemical kinetics study shows that the first-order matrix removal model and the mono contact oxidation model are not suitable for the removal of COD and TN in the system,while the improved stover kincannon model can nicely describe the removal of COD(R²=0.9997)and TN(R²=0.9935)in the system,which can be used as the biochemical kinetic description of the SMHA/OBAF process.