Reusing the generated sludge as Fe source in Fenton process for treating crepe rubber wastewater

Sludge recycling in Fenton oxidation was performed following the simplest procedure for studying the reaction phenomena and the role of Fe using methanol as the model compound and crepe rubber wastewater (CRWW) as the industrial application. CRWW is odorous and high in organics, nitrogen and phosphorus. Despite the capability of degrading hardly decomposable substances, large Fe³⁺ sludge production confines the useful application of Fenton oxidation. This sludge is hazardous due to residual organics adsorption from treated wastewater. Batch-mode experiments were performed at 25 °C and pH 2–3 for 24 h. After neutralization (adjusting pH > 9) and centrifugation, concentrated sludge was applied in the subsequent Fenton run as the Fe source. TOC reductions of 100% and 97% in conventional Fenton and 100% and 77% in sludge reuse systems were achieved for methanol and CRWW solutions, respectively, for initial COD:H₂O₂:Fe²⁺ mass ratio of 1:8:2 with effective reuse cycles. Fe in the sludge system behaved primarily as a heterogeneous catalyst, while dissolved Fe contributed to homogeneous catalytic reactions. Dissolved Fe²⁺ and total Fe were accumulated in sludge runs for enhancing the homogeneous process. Outcomes indicate that the simplest sludge reuse method experimented in this work can be effectively applied as an environmentally and economically promising method.