Effects of Microwave Irradiation on the Color and Turbidity of Wastewater from Paper Recycling

This study aims to determine the general optical properties of wastewater generated during the paper recycling process and to investigate the effects of microwave (MW) irradiation on color properties and turbidity removal. The lowest turbidity values were achieved at the highest MW power (360 W) and the longest irradiation time (60 seconds), that more effective results observed when combined with high-speed centrifugation (4000 rpm). The highest turbidity removal efficiency was achieved in sample YD6, with a reduction of 20.3 NTU, confirming that MW irradiation enhanced the separation of suspended solids when used in conjunction with centrifugation. It was revealed that increasing the centrifugation speed enhanced the turbidity removal efficiency. However, color analysis clearly demonstrated that MW irradiation altered brightness (L*), redness-greenness (a*), and yellowness-blueness (b*) color coordinates to a certain extent. The highest total color difference values were recorded in samples XD1 (∆E: 4.60) and YC2 (∆E: 5.02), indicating that MW treatment induced significant changes in the color composition of wastewater. Moreover, Hue angle (h0) analysis further demonstrated the shift in color composition after MW irradiation and centrifugation, reinforcing the potential of this approach for improving wastewater optical quality. It is notable that when the MW power increases, some optical variations occur in color properties of wastewater samples. The findings of this study may suggest that MW irradiation has potential impact, as a pre-treatment method for wastewater treatment in industrial processes such as paper recycling.