Complete degradation of Orange G by electrolysis in sub-critical water

Abstract

Complete degradation of azo dye Orange G was studied using a 500 mL continuous flow reactor made of SUS 316 stainless steel. In this system, a titanium reactor wall acted as a cathode and a titanium plate-type electrode was used as an anode in a subcritical reaction medium. This hydrothermal electrolysis process provides an environmentally friendly route that does not use any organic solvents or catalysts to remove organic pollutants from wastewater. Reactions were carried out from 30 to 90 min residence times at a pressure of 7 MPa, and at different temperatures of 180–250 °C by applying various direct currents ranging from 0.5 to 1 A. Removal of dye from the product solution and conversion of TOC increased with increasing current value. Moreover, the effect of salt addition on degradation of Orange G and TOC conversion was investigated, because in real textile wastewater, many salts are also included together with dye. Addition of Na 2CO 3 resulted in a massive degradation of the dye itself and complete mineralization of TOC, while NaCl and Na 2SO 4 obstructed the removal of Orange G. Greater than 99% of Orange G was successfully removed from the product solution with a 98% TOC conversion.