Degradation of p-nitrophenol in aqueous solution by microwave assisted oxidation process through a granular activated carbon fixed bed

A microwave (MW) assisted oxidation process was investigated for degradation of p-nitrophenol (PNP) from aqueous solution. The process consisted of a granular activated carbon (GAC) fixed bed reactor, a MW source, solution and air supply system, and a heat exchanger. The process was operated in continuous flow mode. Air was applied for oxygen supply. GAC acted as a MW energy absorption material as well as the catalyst for PNP degradation. MW power, air flow, GAC dose, and influent flow proved to be major factors which influenced PNP degradation. The results showed that PNP was degraded effectively by this new process. Under a given condition (PNP concentration 1330 mg/L, MW power 500 W, influent flow 6.4 mL/min, air flow 100 mL/min), PNP removed 90%, corresponding to 80% of TOC removal. The pathway of PNP degradation was deduced based on GC–MS identification of course products. PNP experienced sequential oxidation steps and mineralized ultimately. Nitro-group of PNP converted to nitrite and nitrate. Biodegradability of the solution was improved apparently after treatment by MW assisted oxidation process, which benefit to further treatment of the solution using biochemical method.