Photodegradation of petrol station wastewater after coagulation/flocculation with tannin-based coagulant

This work investigates the combined treatment of petrol station wastewater by coupling coagulation/flocculation and heterogeneous photocatalysis processes. Coagulation/flocculation was performed using a tannin-based coagulant, Tanfloc. Commercial TiO2, ZnO and Nb2O5 were applied as photocatalysts, after calcination at 500 °C/5 h. In order to evaluate synergic effects, the semiconductor oxides were mixed (50 wt%) and their activities were investigated under UV and VIS radiations. High reductions of absorbance, chemical oxygen demand and elimination of toxicity to Artemia salina was achieved with TiO2–ZnO under UV radiation. Chemical oxygen demand was reduced from 1363 mg L−1 (untreated) to 362 mg L−1 after coagulation/flocculation and finally to 104 mg L−1 after photocatalytic treatment.