Degradation of 3-nitrobenzenesulfonic acid and regeneration of activated carbon under coupled irradiation of microwave and ultraviolet

To solve the problems of high cost and hazardous waste disposal when activated carbon (AC) was used in waste water treatment, the application of coupled irradiation system of microwave (MW) and ultraviolet (UV) for regenerating waste AC and degrading the organic pollutants adsorbed on it were studied. As a typical case, the AC with adsorbed 3-nitrobenzenesulfonic acid (3-NBSA) from electroplating wastewater was treated in the system. In this study, the effect of pH on adsorption efficiency, the adsorption kinetics and adsorption isotherms of 3-NBSA on activated carbon were evaluated. Furthermore, the impact factors of activated carbon regeneration rate and regeneration loss rate were discussed by changing MW power, MW irradiation time, airflow rate, and regeneration times. The results indicated that pH had no obvious influence on the adsorption ability when it ranged from 2 to 8. In addition, the adsorption kinetics was consistent with the pseudo second-order dynamic model and the adsorption isotherms could be described by Freundlich equation. The optimal conditions for the regeneration of activated carbon were MW power of 500 W, MW irradiation time of 10 min and airflow rate of 0.024 m³/h. Under these conditions, the regeneration rate achieved 99.62% and regeneration rate could still reach 90.02% after five full cycles. Activated carbon regeneration rate and the effect of 3-NBSA degradation under the coupled irradiation of MW and UV were better than those under MW irradiation only.