Activated petroleum waste sludge biochar for efficient catalytic ozonation of refinery wastewater.

Large quantities of hazardous activated petroleum waste sludge and wastewaters are generated from petroleum refining. The present disposal of the sludge via incineration or landfill may cause secondary pollution as well as additional costs. Treatment of petroleum refinery wastewater (PRW) by catalytic ozonation process (COP) remains a great challenge of developing low-cost and high-efficiency catalysts. Use of waste sludge derived biochar as catalysts in COP of PRW not only solves the solid wastes and wastewaters problems but also improves profitability. The elements of carbon (C), silicon (Si) and metals originally found in activated petroleum waste sludge contribute to the formation of active sites during pyrolysis. The biochar contains functional C groups, SiO structures, and metallic oxides that promote oxidation through the formation of hydroxyl radicals (OHs) mineralizing petroleum contaminants. Catalytic ozonation of PRW using this sludge biochar (SBC) doubles the total organic carbon removal (53.5%) relative to single ozonation (26.9%). Oxygen (Ox)-, nitrogen (NOx)- and sulfur (OxS)-containing contaminants were decreased by 33.4% (989 vs 659), 58.2% (912 vs 384) and 12.5% (384 vs 336). The present study shows the potential of a "wastes-treat-wastes" process for wastewater treatment.