| The coal gasification industry in China has been rapidly developed and played an important role in new clean and renewable energy market in recent years. However, the arbitrary discharge of coal gasi?cation wastewater(CGW) would cause a serious environmental problem, due to the presence of complicated and considerable amounts of toxic and refractory compounds. Although conventional treatment of CGW quite effective, these processes are still not enough to meet the strict requirements of the National Discharge Standard of China. The biologically pretreated CGW still contains a large number of toxic and refractory compounds as well as their derivatives, with lower biodegradability than the raw wastewater. The wastewater control task has become a bottleneck for the quick development of coal gasi?cation industry in China. Thus, it is very important to find an efficient and cost-effective process for advanced treatment of biologically pretreated CGW, which could enhance biodegradation and remove toxic inhibitory of raw wastewater, further improve effluent quality to meet the requirements of environmental protection and wastewater reuse. In the present work, advanced treatment of CGW was investigated and analyzed employing heterogeneous catalytic ozonation integrated with anoxic moving bed biofilm reactor(ANMBBR) and biological aerated filter(BAF) process and the economical cost and application prospect of the integrated processes were evaluated.Sewage sludge of biological wastewater treatment plant was converted into sewage sludge based activated carbon(SBAC), which supported manganese and ferric oxides as catalysts to improve the performance of ozonation of real biologically pretreated CGW. Results demonstrate that the effects of metal type and roast temperature on catalytic activity were significant. Catalysts exhibit typical mesoporous characteristics with high specific surface area and the high dispersion of transition metal oxides on the SBAC with the multivalence oxidation states increased the number of alkaline group, further increased p Hpzc value of catalysts which was bene?cial to catalytic activity expression. In addition, heavy metals of leaching solution with prepared catalysts were investigated that the main heavy metal concentrations were lower than national requirements. Meanwhile, as compared to that achieved by the fresh catalysts, no remarkable change was observed on the catalytic activity of the prepared catalysts after the tenth successive run, and the COD removal efficiency was only decreased by average 5.4 %, and leaching of Mn and Fe irons were very few, without second pollution for environment.Effects of important operating parameters on the performance of heterogeneous catalytic ozonation of biologically pretreated CGW were investigated. The addition of the prepared catalysts signi?cantly improved the pollutants removal performance of ozonation of raw wastewater without substantial pre-adjustment quality. The treated wastewater were more biodegradable and less toxic than that in ozone alone, and the effluent COD, total phenols(TPh) and TOC concentrations all met class-I criteria of the Integrated Wastewater Discharge Standard(GB18918-2002, China). Meanwhile, the raw and treated wastewaters were analyzed by the GC-MS, the results indicated the catalytic ozonation with the prepared catalysts exhibited higher oxidative activity even completely mineralized toxic and refractory compounds and the residuals were nitrogen heterocyclic compounds(NHCs) and long-chain hydrocarbons compunds. In addition, the removal performance of typical NHCs of raw wastewater was analyzed in catalytic ozonation process. The results showed NHCs were difficult to mineralize by ozone oxidation which caused unsatisfied TN concentration in treated wastewater. Meanwhile, the effects of radical scavengers on TOC removal in ozonation without and with catalysts were performed. The results indicated that the main reaction pathways of catalytic ozonation involved the participation of the highly reactive hydroxyl radicals and the possible catalytic pathway was proposed.A novel system integrating ANMBBR and BAF with short-cut nitrification and denitrification process was investigated for treatment of biologically pretreated CGW. The results shows the system had efficient capacity of degradation of pollutants especially nitrogen compound removal. The best performance was obtained at hydraulic residence times of 12 h and nitrite recycling ratios of 200 %, the effluent COD, NH4+-N, TPh and TN concentrations all met class-I criteria of the Integrated Wastewater Discharge Standard. Meanwhile, compared with traditional A2/O process, the system had higher removal performance of NH4+-N and TN, especially the high toxic loading. Based on activated sludge intolerable limit of toxicity and enhancement of degree of wastewater biodegradability as evaluation criterias, operating parameters of the heterogeneous catalytic ozonation integrated with ANMBBR-BAF process were optimized with maximum biological process. The best performance of the integrated processes were obtained at hydraulic residence times of 6 h, the average removal efficiencies of COD, TOC, NH4+-N, TN and TPh were 73.1, 69.2, 93.3, 76.2 and 98.3 %, the corresponding effluent concentrations were 40.3, 15.4, 2.0, 13.1, 0.5 and 5.0 mg/L(BOD5), respectively, all allowing the discharge top limits to be met. Moreover, the integrated processes showed efficient degradation capacity of toxic and refractory compounds by GC-MS analysis.Pilot-scale study was also carried out to examine the application performance of the integrated processes as advanced treatment of CGW. The results show that the integrated processes had ef?cient and stable capacity of pollutants removal and the effluent quality all met the need of efficient reverse osmosis process which was beneficial to achieving “zero liquid discharge”. Moreover, the cost effect of the integrated processes on the wastewater treatment was evaluated. The new cost with application of catalysts was approximately 0.055 Yuan RMB per ton of wastewater. Compared to single ozone oxidation with the same effluent quality, catalytic ozonation process saved about 0.67 Yuan RMB per ton, while better effluent quality, catalytic ozonation process saved 91.7 % cost. Therefore, the integrated processes with efficient, stable, economical and sustainable advantages were suitable for advanced treatment of real CGW. |
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