Study On Advanced Treatment Of Coal Chemical Wastewater By Pilot-scale Microbubble Ozonation Combined With Biological Treatment Process

In this study,a pilot-scale microbubble ozonation combined with biological treatment process was used for the advanced treatment of coal chemical wastewater.The operating performance of the pilot-scale process was evaluated,and the influences of operating parameters on its performance were investigated.The difference in performance bwtween the pilot-scale process and the full-scale plant was compared.In addition,a two-stage treatment of the pilot-scale process was carried out and the performance was evaluated to meet the more stringent discharge standard.Furthermore,a reaction rate model was constructed based on simulation ozonation experiments and a neural network prediction model was constructed based on the operating data of pilot-scale process to predict the oxidation capacity of microbubble ozonation.The results achieved in this study were shown as follows.1)The average COD removal efficiency was 34.5%and the average UV₂₅₄ removal efficiency was 52.5%in microbubble ozonation of the pilot-scale process,and the BOD/COD increased from 0.13 to 0.25,indicating the significant biodegradability improvement.The ratio of ozone dosage/influent COD amount was a key operating parameter for microbubble ozonation treatment,and there was a significant positive correlation between the ratio of ozone dosage/influent COD amount and COD removal efficiency.The optimal ratio of ozone dosage/influent COD amount was determined as0.4～0.5.The BOD concentration increased in microbubble ozonation,and there was a significant positive correlation between the increased BOD amount and removed COD amount.In biological treatment,the average COD removal efficiency was 11.0%and the average BOD removal efficiency was 47.1%.The contribution of BOD removal to COD removal was over 80%.2)The optimal operating conditions for the two-stage treatment of the pilot-scale process was raw water flow rate of 5 m³·d^-1 and recirculation flow rate of 5 m³·d^-1.Under this condition,the average COD removal efficiency of the first-stage treatment was 53.2%,and the average COD removal efficiency of the second-stage treatment was 21.2%,and as a result,the overall average COD removal efficiency of the two-stage treatment was74.1%.Compared with the one-stage treatment,the COD removal efficiency increased20%,while the operating cost increased 30%approximately.The COD concentration of the effluent after two-stage treatment could be lower than 50 mg·L^-1 to meet the enterprise discharge standard requirements,when the COD concentration of the influent was controlled below 150 mg·L^-1 and the COD removal efficiency was higher than 65%.The correlation analysis showed that increase in COD removal in microbubble ozonation could increase COD removal in biological treatment.Therefore,it is feasible to improve the total COD removal efficiency in two-stage treatment,in order to improve the effluent quality and meet the more stringent standard.3)The kinetic model of microbubble ozonation reaction was established by synthetic wastewater experiments with specific organics,and COD concentration decreasing trend and removal efficiency with time could be predicted in microbubble ozonation.It was found that the reaction rate constant of COD removal in microbubble ozonation was related to the molecular structure of the organics.The ozonation reaction rate constant of organics containing polyphenylene rings and branched chains was slower than that of straight-chain organics.A neural network（BPNN）prediction model of the COD removal performance using the ratio of ozone dosage/influent COD amount as input parameter was developed based on the pilot plant operation data.The prediction model showed good robustness and adaptability,and could predict the treatment capacity of microbubble ozonation accurately.