Study On Regeneration Of Powdered Activated Carbon Using Wet Oxidation

Dual-membrane (MF/UF-RO) process is widely used in the reuse of wastewater.While the process produces70percent recycled pure water, it will also produce30percent RO concentrate (ROC) which containing high concentrations of pollutants aswell. If ROC is discharged directly into the environment, it will have a very negativeimpact. Powdered activated carbon (PAC) adsorption is one of the preferred treatmentprocesses for ROC. Countries around the world use a large amount of PAC for waterand wastewater treatment each year, and the usage increases year after year. AfterPAC adsorbs contaminants, itself becomes toxic and hazardous solid waste, ifimproperly disposed it can cause secondary pollution, if disposed as solid waste, thecosts of solid waste disposal will increase. Therefore, regenerating and recyclingwaste PAC has important environmental and economic benefits.In this study, a preliminary study was conducted to regenerate PAC with wetoxidation method. Wet oxidation method can avoid secondary pollution and reduceregeneration losses. It is suitable for the regeneration of PAC which adsorbs refractoryorganics. The main factors affecting wet oxidation regeneration were considered to bethe regeneration temperature, regeneration time and oxygen dosed and so on. Thepressure of oxygen dosed was determined as0.1MPa in the wet oxidation reactor,and the regeneration temperature was set as150℃,200℃and250℃, respectively,and the regeneration time as0.5h and1h.This paper studied six regeneration conditions. The best combination wasregeneration time of1h with a temperature of200℃. Under this condition PACregeneration rates for organic indicators of DOC, COD, UV254were80.54%,83.92%,87.73%, respectively. Under the same regeneration time, the DOC and UV254regeneration rates for PAC were the highest at200℃, because the pore structure wasbest recovered. The ratio of microporous for regenerated carbon was closest to that ofthe new carbon, and the ratio of microporous and mesoporous of regenerated and newcarbon best closes to100%. The COD regeneration rate for PAC was highest at250℃,the oxidative decomposition of pollutants in the pores is more thoroughly, but porestructure was destroyed after regeneration to some extent.When the regeneration time was1h, temperature of200℃could be better torecover the microporous structure for saturated carbon. The microporous structurecould not be recovered at250℃, and size of part pores increased to the mesoporous pore due to the high temperature, which damaged the pore structure of PAC. When theregeneration temperature was200℃, the micropores and pore structure for saturatedcarbon could be well recovered within regeneration time of1h, the recovery wasbetter than the regeneration time of0.5h.The DOC and UV254removal rate for regenerated carbon showed an decreasingtrend overall with cycle number of regeneration increasing. The pore structure of PACwas destroyed worslly when the fourth regeneration, which resulted in thesignificantly lower DOC removal rate. The UV254removal rate performanced betteroverall, which meant the performance of PAC for UV254was less impacted by therecycle number.When the regenerated PAC used for a adsorption of ROC with a dosage of0.9g/L, the regeneration rates characterized by DOC and UV254for recycled PACdecreased with the cycle number of regeneration increasing. The regeneration rate ofDOC was linearly related with the amount of microporous pore volume and surfacearea of the regenerated carbon.