Potential Of Petrochemical Sludge-derived Biochar Assisted Ozonation Treatment Of Recalcitrant Wastewater

Waste disposals and wastewater discharges are hindering sustainable development of petrochemical industries.In the present study,the excess activated sludge(EAS)of petrochemical industries was prepared to the sludge-derived biochar(SBC)by pyrolysis.The SBC was used as a catalyst for catalytic ozonation process(COP)of simulated petrochemical wastewater.Structures and properties of SBC catalysts were characterized.Mineralization efficiencies and oxidation mechanisms of refractory organic chemicals(ROCs)in SBC aided COP(SBC-COP)were investigated.SBC catalysts showed well-developed mesoporous structures,however,owned markedly low total surface areas(?143m~2/g)and total pore volumes(?0.2cm~3/g).Inorganic impurities originally in EAS were deposited into SBC and caused blockages of pores during pyrolysis.However,it contributed the rich surface functional groups and chemical bonds of SBC catalysts.Water in EAS acted as the activator of SBC preparation by pyrolysis.SBC catalysts showed very low adsorption towards ROCs in wastewater but significantly high catalytic activity in COP.The total organic carbon(TOC)removals(72%and 86%)of nitrobenzene and benzoic acid solutions doubled in SBC-COP relative to single ozonation(34%and 49%).The ozonation catalysis was via free radical mediation oxidation.Surface function groups of carbon such as O-H,aromatic C=C or C=O,and asymmetric Si-O-C as well as inorganic components including Si,Al,Zn,Mg and Fe oxides constitute active sites of SBC catalysts.The composite active sites accelerated ozone decomposition to free radicals in SBC-COP and then promoted mineralization of ROCs.The present study showed the potential of SBC catalysts for efficient COP treatment of recalcitrant wastewater with an advantage of the cost effectiveness through “wastes-treat-wastes”.