Study On The Mechanism Of CaO Based Simultaneously Coupled Catalytic Ozonation And Biodegradation For Coking Tail Water Treatment

As a great coal-using country,China produces up to 300 million tons of coking wastewater from coking chemicals every year.Meanwhile,the coking tailwater produced by partial biological treatment with characterization of refractory organic substances remaining and poor biodegradability was required for further treatment by advanced oxidation processes（AOPs）.The catalytic ozonation process is an excellent AOP with inexpensive and widely applicable features,and usually meets better effects coupled with biodegradation.However,the role and mechanism of simultaneously coupled catalytic ozonation and biodegradation（SCCOB）for coking tailwater treatment needs to be investigated.Therefore,in this work,catalyst with high efficiency was screened to catalyze ozonation and SCCOB system was constructed to improve the effect of coking tailwater treatment.Firstly,characteristics of coking tailwater quality was analyzed,with chemical oxygen demand（COD）of 370～420 mg/L,B/C of 0.013 and the presence of refractory pollutants such as metal ions and phenols.Afterwards,among several common and easily available metal oxide catalysts such as CaO and Mg O,the most suitable catalyst CaO was screened and its optimal dose was determined to be in the range of 0.6～1.0 g/L based on two factors:degradation efficiency and p H.There were two mechanisms of CaO based catalytic ozonation mainly included:oxidation and coagulation.The main mechanism of oxidation was the degradation of organic matters by·O₂^-,while the coagulation played an important role in the removal of metal ions.Finally,about 20%of the organic substances,73%of the total phenols and 90%of the metal ions were slashed,and the B/C was boosted to 0.15.But there was an insufficient mineralization,so the coupling of biodegradation for deeper treatment of the catalytic ozonation effluent was necessary.Secondly,a CaO based SCCOB system was constructed to investigate its effect on coking tailwater treatment.After selection,quartz balls with stable structure,good fluidization and high loading efficiency were used as carriers,and the loading of CaO was completed by adhesive bonding method and the loading method was optimized by response surface model（RSM）.The coupled reactor based on quartz ball carriers was operated continuously for 68cycles,and the effluent COD consistently met the indirect discharge standard for coking tailwater.The coupled reactor had significant advantages against to catalytic ozonation:the removal rates of COD,UV254 and total phenols were increased by 20%,37%and 14%,respectively.The effluent color was further reduced to 2 times,and the sprouting rate of green beans soaked in effluent was increased to 63%.In summary,this study successfully constructed a CaO based SCCOB system to achieve effective treatment of coking tailwater.The addition of the biodegradation part increased the treatment capacity and made the effluent meet the indirect discharge standard,with several indicators showing better results than catalytic ozonation treatment.These results can provide theoretical reference and technical guidance for industrial wastewater treatment.