Feasibility of UVA photocatalytic post-treatment of molasses wastewater: Effects on melanoidins removal, mineralization and oxidation of ammoniacal-nitrogen

Abstract

The brown color of molasses wastewater is due to the presence of melanoidins which are toxic to human health and environment. In this study, combination of coagulation-flocculation process with UVA-photocatalytic degradation of raw and diluted molasses wastewater in the presence of zinc oxide (ZnO) and titanium dioxide (TiO2) as photocatalyst was investigated. The effect of various operating parameters, such as light irradiation, aeration, catalyst dosage and pH of molasses wastewater on the photocatalytic degradation process was examined. The pre-treated diluted molasses wastewater (2 DF) showed greater performance compared to pre-treated raw for both photocatalysts due to high penetration of light into the wastewater. The formation of •OH enhanced color intensity reduction rate of pre-treated raw and 2 DF molasses wastewater in the presence of light irradiation and aeration. The color removal efficiency of pre-treated raw and 2 DF molasses wastewater was better in alkaline medium (pH 10) when ZnO used as photocatalyst, meanwhile it achieved higher removal efficiency in acidic medium (pH 4) when TiO2 was used as photocatalyst. The mineralization and oxidation of ammoniacal-nitrogen of molasses wastewater showed enhanced performance in photocatalytic treatment.