The role of added oxidising agents in assisting the photocatalytic treatment of olive mill wastewater using a metal-free g-C3N4 optical semiconductor

Abstract

Olive mill wastewaters (OMW) consist of high organic contents and are harmful to aquatic and terrestrial biota. Heterogeneous photocatalysis is a technology that can be operated under mild conditions to remove pollutants in the liquid phase. In the present work, graphitic carbon nitride (g-C3N4, hereafter referred to as GCN) is studied for the first time as a metal-free photocatalyst for OMW treatment. The integration with peroxidation (H2O2), Fenton (Fe2+/H2O2 at both acidic and natural pH), chlorination (HOCl/ClO- ) or persulfate (PS) activation is also investigated. This catalyst potentiated the activation of these oxidants, and H2O2 was identified as the best option to achieve high removals of total phenolic content - TPh (87.5 +/- 0.3 %), dissolved organic carbon - DOC (63.8 +/- 0.4 %) and chemical oxygen demand - COD (87.7 +/- 0.6 %), without need to add iron or adjust the pH. The stability and reusability of the GCN material in the H2O2-assisted photocatalytic treatment of OMW give rise to new possibilities for treating these waste waters.