Synergistic degradation of acid blue 113 dye in a thermally activated persulfate (TAP)/ZnO-GAC oxidation system: Degradation pathway and application for real textile wastewater

The performance of a binary persulfate activation system based on the simultaneous use of heat (TAP) and ZnO coated granular activated carbon (ZnO-GAC) catalyst was investigated for the degradation of Acid Blue 113 (AB113) azo dye and the treatment of textile industry wastewater. FESEM, XRD, FTIR, EDX-mapping and BET analyses confirmed the successful loading of ZnO nanoparticles onto the GAC substrate. The effect of five independent variables on AB113 removal in the TAP/ZnO-GAC oxidation system was optimized by a 5-level full central composite design (CCD). All experiments were performed in a 6250 mL volume reactor. Adequacy and validity of the proposed model were confirmed with p-value < 0.0001 and R-2 = 0.9994. The optimum values for solution pH, reaction time, persulfate (PS) concentration, ZnO-GAC dosage, and solution temperature were obtained to be 4.7, 50 min, 4.2 mM, 2.5 g/L, and 70 degrees C, respectively. Under these conditions, the maximum removal efficiency of AB113 in PS/ZnO-GAC, TAP, and TAP/ZnO-GAC oxidation systems was 26, 83 and 94.2%, respectively. The synergistic effect of ZnO-GAC on TAP oxidation system reduced the apparent activation energy by approximately 83%. The naphthalen-1-ol, phthalic acid, malonic acid, ethane-1,2-diol, and oxalic acid were the most abundant intermediates produced during AB113 degradation. Radical scavenging experiments showed that SOZ was the predominant radical species in the TAP/ZnO-GAC system. The optimized TAP/ZnO-GAC process effectively improved the biodegradability of real textile wastewater samples (BOD/COD > 0.4).