Reducing agent-enhanced printed circuit board sludge-based Fenton process for the efficient treatment of coking wastewater: Performance, optimization and mechanism.

Coking wastewater (CWW), characterized by complex composition, high toxicity from phenolic compounds (PCs), and recalcitrant chemical oxygen demand (COD), poses significant treatment challenges. This study innovatively repurposes printed circuit board sludge (PCBS) as a low-cost heterogeneous catalyst in a Fenton-like advanced oxidation process activated by sodium thiosulfate (STS) for simultaneous removal of PCs and COD. Key parameters (acid-leaching (H2SO4): 1.14 mol/L; PCBS dosage: 1.34 g/L; STS: 0.03 mmol/L; H2O2: 79.88 mmol/L) were optimized via Box-Behnken Design response surface methodology. The PCBS/H2O2/STS system exhibited excellent performance in removing PCs and COD from CWW, achieving the model predicts removal efficiencies of 95.51 % and 56.32 %, respectively, under optimized conditions. Through experimental verification, the experimental removal efficiency of PCs and COD are 95.66 % and 57.74 %, respectively, with a difference of only 1.42 % and 0.15 % from the estimated values of the model. The degradation proceeds through a dual-phase mechanism: (1) heterogeneous catalysis on PCBS surfaces, where Fe/Cu species activate H2O2 to generate HO•, and (2) homogeneous reactions driven by leached Fe3+/Cu2+ ions, which are reduced by STS to Fe2+/Cu+, further reacting with H2O2. Notably, hydroquinone and benzoquinone intermediates act as electron mediators, establishing a self-sustained redox loop that minimizes STS consumption. This 'waste-to-resource' strategy repurposes PCBS as both a catalyst and metal source, while the reduction effect of STS overcomes the limitations of traditional Fenton processes. Overall, the PCBS/H2O2/STS system provides an efficient, sustainable solution for CWW treatment and pollutant degradation.