Study On The Adsorption And Regeneration Of Activated Carbon In Advanced Treatment Of Pharmaceutical Wastewater

The pharmaceutical manufacturing industry not only makes important contributions to China’s economic construction and people’s health,but also discharges tens of thousands of tons of pharmaceutical wastewater with high concentration and complex composition.It is difficult to meet increasingly stringent emission requirements only by relying on secondary treatment processes.Activated carbon adsorption technology can be applied to the advanced treatment of pharmaceutical wastewater due to its simple operation and stable treatment effect.With the increasing application of activated carbon,the disposal of saturated carbon should also be paid more attention.The regeneration of saturated activated carbon can not only save the cost of activated carbon,but also avoid secondary pollution that may be caused by improper disposal of waste activated carbon.Based on this background,in this study,the application of activated carbon adsorption in advanced treatment of pharmaceutical wastewater was investigated,and the saturated activated carbon was regenerated by ultrasonic radiation method,ozone oxidation method and high temperature heating method.The main research contents and conclusions are as follows:First,the effect of activated carbon adsorption in the advanced treatment of pharmaceutical wastewater was investigated.The selected coal granular activated carbon with a particle size of 1.0～2.3 mm had the best effect when the dosage was 6.25 g/L and the adsorption was 3.5 h.The removal rates of COD and chroma were 64.5%and 58.9%,respectively.After impregnation with 0.5 mol/L HCl for 12 h,the removal rates of COD and chroma of the modified carbon increased by 6.2%and 8.1%,respectively,compared with those before modification.The surface of modified carbon was smoother,the pore structure was more developed,and the content of acidic oxygen-containing groups on the surface was increased.Both increasing the temperature and decreasing the pH could improve the adsorption effect of the two activated carbons before and after modification.The adsorption behavior of the two active carbons conforms to the quasi-second-order kinetic model.Both Langmuir and Feundlich models could describe the adsorption process of the two actived carbons.Secondly,ultrasonic radiation method,ozone oxidation method and high temperature heating method were used to regenerate the saturated activated carbon,and their conditions were optimized by single factor test.Under the conditions of frequency 20 kHz,power density 2.6 W/mL,saturated actived carbon dosage 45 g/L,0.2 mol/L NaOH+5%ethanol as regeneration solution,ultrasonic irradiation for 30 min,the regeneration rate was 78.6%.The ozone oxidation method had a regeneration rate of 72.7%under the conditions of ozone dosage 63.7 mg O3/g GAC,pH 9.0 and 30℃.The high temperature heating method had a regeneration rate of 97.2%under the condition of heating at 700℃ for 60 min.Finally,three regeneration methods under optimized conditions were compared.After five times of regeneration,the regeneration rate of high temperature heating method was the most stable,the regeneration rate was still 95.5%after five times of regeneration,but the mass loss was high.Followed by the ultrasonic radiation method and ozone oxidation,their quality loss was low and the average mass loss of the 5 times of regeneration was 1.56%and 0.81 respectively.SEM,BET,Boehm titration,pH titration,TG,Sieving method were used to characterize the activated carbon after the three methods were regenerated once.SEM showed that the organic matter covered by the activated carbon surface was removed to varying degrees after regeneration.The physical structure and surface functional group analysis showed that the BET specific surface area,micropore area,micropore volume,basic functional group,carboxyl group,and phenolic hydroxyl group content were strongly related to the adsorption performance.TG analysis confirmed that the adsorption process was mainly chemical adsorption.The particle size distribution test showed that the proportion of small particle size particles increased after regeneration by ultrasonic radiation method and high temperature heating method,and the smaller the particle,the better the adsorption performance and regeneration effect.In the regeneration process of activated carbon,the ultrasonic radiation method was achieved by the combined actions of cavitation effect,mechanical effect and thermal effect.The hydroxyl radicals played an important role in the ozone oxidation method.The desorption and decomposition simultaneously existed in the regeneration process of the high temperature heating method.