Improvement of spent activated carbon regeneration by wet oxidation processes

Abstract Activated carbons saturated with p -nitrophenol were regenerated under subcritical conditions by means of wet oxidation, analyzing the effect of temperature (160–200 °C) and oxygen partial pressure (3–12 bar). The research intended to achieve two main objectives: (a) to restore the carbons adsorption performance and (b) to get insight about the p -nitrophenol oxidation process and how it can be influenced by the presence of the adsorbent. Based on the contaminant oxidation mechanisms, which was defined as a series of radical processes, a kinetic model was developed. The model was created by COMSOL MULTIPHYSICS software, and allowed obtaining characteristical parameters. Further comparison between theoretical and experimental results showed the suitability of the model in the whole range of experimental domain. Subsequent application of this model to regeneration experiments confirmed the need of developing a new model in the latter case, since the presence of carbon involved a significant modification of kinetic parameters, which was related to the catalyzing action of the adsorbent. It was also found that both temperature and pressure affect the p -nitrophenol degradation process as well as porosity regain of the carbons. Values of p -nitrophenol regeneration efficiency up to 87% for the highest values of temperature and oxygen partial pressure.