| Phenol is frequently present in various ammonia-containing wastewaters.Therefore,it is essential to simultaneously remove ammonia and phenol from wastewater.The inhibition of phenol on microorganisms,especially nitrifying bacteria,however,which make it difficult for the traditional biological treatment process to achieve high-efficient ammonia and phenol removal.Consequently,it is of great significance to develop a new process which could simultaneously remove ammonia and phenol from wastewater.A novel step-feed A/O-BAF process was proposed for the treatment of ammonia-containing phenol wastewater in this study.The process utilizes the aerobic and anoxic zones in the filter to realize nitrification and denitrification due to its ability to take advantages of both a step-feed A/O process and the biological aerated filter.At the same time,a major fraction of phenol as carbon source was initially degraded by denitrifying bacteria in the anoxic zone.Subsequently,the residual phenol was biodegraded in the aerobic zone,thus realizing the simultaneous removal of ammonia and phenol from the wastewater.In this study,a system with glucose as single carbon source was used to start up to realize simultaneous ammonia and phenol removal by gradually increasing phenol concentration.Furthermore,the key parameters such as influent flow distribution ratio were optimized under long-term operation conditions.Additionally,the optimal operation parameters of the process were determined through investigating the removal efficiency at different influent ammonia and phenol concentrations and analyzing the variation of effluent quality among each stage with different influent flow ratio and phenol concentration.UV-Visible Spectra(UV-Vis),Fourier Transform Infrared Spectroscopy(FT-IR)and Three-Dimensional Excitation Emission Matrix Fluorescence Spectroscopy(3D-EEM)were used to analyze the components of effluent.Moreover,EPS component analysis and high throughput sequencing were applied to further reveal the characteristics of the biofilm and the molecular biological mechanism of ammonia and phenol removal with the aim to provide theoretical support for the design and operation of the process in the future.The main conclusions of this study are as follows :(1)A step-feed multi-stage A/O-BAF system was established through gradually adding phenol instead of glucose to become single carbon source.Long-term operation results show that the influent flow ratio significantly affects the ammonia removal performance,but has no significant effect on the removal of COD and phenol.The optimal ammonia and phenol removal efficiency of the three-stage BAF were obtained at the influent flow ratio of 4:3.5:2.5.The TN,ammonia,phenol and COD removal rates reach 80.3%,99.5%,99.9% and 99.5%,respectively.The influent phenol concentration has a significant effect on the ammonia removal performance.The effluent TN concentration can be controlled below 15 mg/L when the influent phenol concentration increaseed from 126 mg/L to 420 mg/L.However,the nitrification will be inhibited when influent phenol concentration above 420 mg/L.The denitrification will be inhibited due to insufficient carbon source when the influent phenol concentration is below 120mg/L.Moreover,a large amount of phenol can be detected in the effluent when the influent phenol concentration reaches 756mg/L.The optimal ammonia and phenol removal performance of the system were obtained at the influent phenol and COD concentrations of 336 mg/L and 800 mg/L,while the TN removal rate reach around 84.1%.The system is not ideal for the treatment of high ammonia wastewater,mainly due to the low carbon to nitrogen ratio in the influent.As the phenol concentration increased from 168 mg/L to 756 mg/L,the total biomass of the reactor increased,but the secretion of protein and polysaccharide in EPS was severely inhibited.Furthermore,the EPS component in the aerobic zone was higher than the anoxic zone and the protein content was significantly higher than polysaccharides.The polysaccharides are mainly distributed in TB-EPS,and the proteins are more evenly distributed in the three-layer EPS.(2)The effluent at different influent phenol concentration was analyzed by Fourier Transform Infrared Spectroscopy and UV-Visible Spectroscopy.It was found that phenol cannot be detected in the effluent of each stage when the influent phenol concentration was 168 mg/L.However,when the concentration increased to 504 mg/L,there was no phenol in all aerobic zones,while a large amount of phenol was detected in the effluent of the anoxic zone.This was indicated that the system has strong resistance of phenol-loading.The results of Three-Dimensional Fluorescence Spectroscopy showed that a considerable amount of phenol and aromatic proteins were detected in the aerobic and anoxic zones when the influent phenol concentration was higher 756 mg/L.(3)High-Throughput Sequencing carrying OTU at low influent phenol concentration(168mg/L)and high influent phenol concentration(756mg/L)showed that the species abundance and diversity index increased with the phenol concentration rising.The species abundance and diversity index of anoxic area were higher than aerobic area.The higher abundance of phylum among all stage were Proteobacteria,Bacteroidetes and Firmicutes.The microbial community structure was significantly affected by phenol concentration.Gammaproteobacteria,Flavobacteriia,Clostridia,Betaproteobacteria and Bacilli account for high proportion in each zone when the influent phenol concentration was 168mg/L.While,Betaproteobacteria,Gammaproteobacteria,Deltaproteobacteria,Clostridia,Bacteroidia,Epsilonproteobacteria,Alphaproteobacteria and Anaerolineae had a high proportion in each zone when the concentration of phenol in the influent was 756mg/L.The dominant genera among each zone were Acinetobacter,Pseudomonas,Chrysolobacterium and Paenisporosarcina when the influent phenol concentration of the reactor was 168mg/L.Moreover,Clostridium sensu stricto,Chlorobium,Longilinea and Alkaliphilus were the dominant genera in each anoxic area,while Alishewanella and Pseudoxanthomonas were the dominant genera in each aerobic zone.The dominant genera among each section of the system were Thiothrix,Hydrogenophaga and Arcobacter,while Methanothrix,Syntrophorhabdus and Pelotomaculum were the dominant genera only in each anoxic zone when the concentration of phenol in the influent was 756mg/L.With nitrifying bacteria greatly reducing under the condition of high influent phenol concentration,some anoxic microorganisms were found in the aerobic zone and a wide variety of phenol degrading bacteria appeared.These molecular biological results are closely related to the performance of ammonia and phenol removal. |
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