Removal of high concentration p-nitrophenol in aqueous solution by zero valent iron with ultrasonic irradiation (US-ZVI)

► High concentration PNP can be reduced into the nontoxic p-aminophenol by US-ZVI. ► High removal efficiency of PNP is resulted from the synergistic reaction of ZVI and US. ► The reaction pathway of PNP in the US-ZVI system is proposed. ► Processing parameters of the US-ZVI system were optimized seriously.