| Electroplating wastewater not only contains large amounts of heavy metals andcyanide, but also includes a high concentration of sodium3-nitrobenzenesulfonate (3-NBSA)and other organic matters. Because of their stable structure and toxicity, these organicmatters are hazardous to the soil and the growth of plants and animals, so the treatmentof3-NBSA from electroplating wastewater is very necessary, adsorption is one of themost rapid, energy-saving and efficient way to remove contaminants from theenvironment. This paper studies the adsorption effect of3-NBSA on activatedcarbon(AC), and to solve the problems of high cost and hazardous waste disposal whenAC was used in wastewater treatment, the coupled irradiation system of microwave(MW) and ultraviolet (UV) was applied to degrade the3-NBSA adsorbed on AC andregenerate the waste AC harmlessly.This paper examined the influence of AC kind, pretreatment method and pH onadsorption efficiency of3-NBSA, and the adsorption kinetics and adsorptionthermodynamics were also studied. The results showed that the adsorption capacity ofcoconut shell activated carbon (14mesh to18mesh) which was pretreated by5%dilutehydrochloric acid was the maximum, and pH had no obvious influence on theadsorption ability when it ranged from2to8. In addition, the adsorption kinetics wasconsistent with the pseudo second-order dynamic model and the adsorption isothermscould be described by Freundlich equation.The adsorption type was physical adsorption.The impact factors of activated carbon regeneration rate and regeneration loss ratewere discussed by changing MW power, MW irradiation time, airflow rate, andregeneration times. The results indicated that optimal conditions for the regeneration ofactivated carbon were MW power of500W, MW irradiation time of10min and airflowrate of0.024m3/h. Under these conditions, the regeneration rate achieved99.62%andregeneration rate could still reach90.02%after five full cycles. Original activatedcarbon and activated carbon after regeneration were characterized by the method ofBoehm titration and BET techniques, and it was found that with increase of theregeneration times, the amount of surface acidic groups reduced and basic groupsincreased. The specific surface area of activated carbon after regeneration was889.742m2/g, total pore volume was0.4482cm3/g, and saturated adsorption amount ofN2was300.95cm3/g, which were92%,88.23%and91.64%of the original activatedcarbon, respectively. After regeneration, adsorption isotherms of activated carbon alsocould be described by Freundlich isotherm, and its adsorption capacity returned to95.89%of original activated carbon.By comparison microwave-ultraviolet coupled system with microwave system, it proved that under the microwave-ultraviolet coupled irradiation, activated carbonregeneration effect was99.62%and3-NBSA salinity was31.61%, while they were only86.51%and3.68%under the microwave irradiation.Study on degradation mechanism of3-NBSA suggested that almost all of thesulfonic acid groups were mineralized to SO2, partial of nitro groups were degraded toNOxand NH3. In the reaction system, O2and H2O generated·OH, O3and other oxidantsunder UV irradiation. These oxidants further reacted with benzene ring to generatebenzoquinones which were extremely unstable and easy to generate aldehydes, ketones,organic acids and other intermediates. If sufficient oxidants were adequate, theintermediates would be oxidized to CO2, H2O and so on. |
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