Study On The Treatment Of Caprolactam Wastewater By Sulfite Oxidation Combined With Biological Process

The wastewater from caprolactam production contains macromolecules such as benzene ring and long alkane which are difficult to degrade.Advanced oxidation method has better treatment effect on refractory organic matter,among which the advanced oxidation technology based on sulfate radical(SO₄^·-)has the characteristics of high oxidation capacity and strong mineralization capacity compared with other oxidation technologies.However,it has some problems such as high toxicity,high cost and easy to cause secondary pollution.Therefore,it is necessary to find an efficient oxidizer that can replace persulfate,which has emerged in recent years due to its advantages of low toxicity and cost.Biochar-based catalysts can increase the activity of biochar-based catalysts while reducing metal ion leaching.In this paper,biochar supported transition metal cobalt catalysts were prepared and used to catalyze sulfites to generate oxidizing free radicals(SO₄^·-,SO₅^·-,SO₃^·-and ¹O₂)for the degradation of macromolecular organic compounds in caprolactam wastewater.The removal effects of different reaction systems and different influencing factors on caprolactam wastewater were systematically investigated.The reaction mechanism was explored,and the wastewater after oxidation treatment was treated by biological treatment.The optimal conditions of caprolactam wastewater treated by sulfite oxidation combined with biological treatment were investigated,which provided reference for the treatment of practical industrial wastewater.The specific research contents and main conclusions are as follows:（1）Biochar was prepared from peanut shells under oxygen restriction condition.After acid modification,transition metal cobalt was supported by impregnation method.Biochar based catalyst（CoBC）supported cobalt metal was prepared under300℃oxygen restriction condition.CoBC was characterized by scanning electron microscopy（SEM）,X-ray energy spectroscopy（EDS）,X-ray diffraction（XRD）,X-ray photoelectron spectroscopy（XPS）and Fourier Transform infrared spectroscopy（FTIR）.The results showed that CoBC was a kind of biochar based catalyst with large specific surface area,active free radicals,uniform distribution of Co on the material,and many functional groups.（2）The catalytic activity of CoBC was further discussed,the influencing factors of activated sulfite by CoBC were optimized by response surface methodology,and the stability and reusability of the material were explored.CoBC has strong catalytic activity.When the dosage of CoBC is 2.5 g/L,the dosage of sodium sulfite is 4 g/L,the initial p H is 8,and the dissolved oxygen is 9.1 mg/L,the removal effect of caprolactam wastewater is the best.The results of continuous repeated experiments and FTIR analysis showed that CoBC had good stability and reusability.（3）The possible reaction mechanism was explored by the characterization of the catalyst and the analysis of water samples after the reaction.The CoBC catalyst before and after the reaction was characterized by SEM,EDS,XRD,XPS and FTIR.The changes of free radicals and water quality were analyzed by GC-MS and EPR analysis,and the activation effect of CoBC on the oxidation reaction was confirmed.The main active substances in the reaction process are ¹O₂,SO₄^·-and·OH,and most of the organic matter is degraded after the reaction.（4）In order to treat industrial wastewater thoroughly,caprolactam wastewater treated by oxidation process was further treated by SBBR process,and the process parameters of SBBR were optimized,and the removal effect was the best when the hydraulic retention time was 4 h,the aerobic anoxic time ratio was 1.5 h:2.5 h,and the effluent water quality was stable after a long time of operation.It shows that the wastewater treated by oxidation has better biodegradability.