| After the traditional physical-chemical pretreatment and biological treatment the effluent of coal chemical wastewater is difficult to meet the corresponding wastewater discharge standards,and still belong to typical toxic and refractory industrial wastewater.Therefore,the advanced treatment of bio-treated coal chemical wastewater is necessary for further removal of refractory and toxic pollutants.A novel combination of microbubble catalytic ozonation and biological treatment process was used in this study to treat a real bio-treated coal chemical wastewater.The performances of microbubble catalytic ozonation,biological treatment and total system were evaluated.The performance of this combination system was optimized.The main refractory organic pollutants in wastewater and their removal mechanism were analyzed.The results showed that when ozone dose was 0.34 kg·d-1 in microbubble catalytic ozonation,the average COD removal efficiency was 26.35%,the average COD loading rate removed was 1.27 kg·(m3·d)-1,the ratio of ozone amount consumed to COD amount removed was 2.72 mg·mg-1 and the average UV254 removal efficiency was 53.72%.Moreover,the BOD5/COD value increased from initial 0.038 to 0.30,indicating the significant improvement of biodegradability.The average COD loading rate removed was0.26 kg·(m3·d)-1 and the average ammonia nitrogen removal efficiency was 52.9%in the following biological treatment.The optimal operation results of this combination system showed that the better performance of the combination system could be achieved when the system effluent reflux ratio was 30%and the ratio of ozone dosage to influent COD was0.44 mg·mg-1.In this case,for microbubble catalytic ozonation,the COD removal efficiency was 42.5%,the ratio of ozone consumed to COD removed was 1.38 mg·mg-1and the ozone utilization efficiency was 98.0%.For biological treatment,the COD removal efficiency was 42.3%.For the combination system,the total COD removal efficiency was 66.7%,the average final effluent COD concentration was 91.5 mg·L-1 and the estimated total ratio of ozone consumed to COD removed was 0.68 mg·mg-1.In addition,activated carbon,cinder and ferric oxide could be used as suitable ozone catalyst and honeycomb ceramic carrier could be used as suitable biofilm carrier,considering their performance and cost.The GC-MS,UV-Vis spectra and fluorescence excitation–emission matrix(EEM)spectra of bio-treated coal chemical wastewater were analyzed during combination treatment.The nitrogen-containing heterocyclic aromatics were identified to be the main refractory contaminants in bio-treated coal chemical wastewater,and microbubble catalytic ozonation was effective for degradation of nitrogen-containing heterocyclic aromatics,to generate low-molecular-weight organics and improve wastwater biodegradability.Moreover,the efficient degradation of nitrogen-containing heterocyclic aromatics by microbubble catalytic ozonation treatment resulted in ammonia nitrogen release which could be removed in the following biological treatment. |
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