Three-dimensional electro-Fenton system with iron-carbon packing as a particle electrode for nitrobenzene wastewater treatment

Traditional Fenton oxidation is an effective method for reducing pollutants that are difficult to degrade. Owing to the large amounts of Fe(II), acids, and alkalis added in the reaction, large amounts of Fenton sludge are produced, increasing treatment costs and restricting the method’s application. In this study, we developed a three-dimensional electro-Fenton system by adding iron-carbon filler and investigated the effects of different electrolytic cell structure arrangements, particle electrode dosages, sponge iron (SI) to granular activated carbon (GAC) dosage ratios, current densities, H₂O₂ dosages, and cathodic aeration on nitrobenzene (NB) wastewater treatment. The optimal system conditions were a particle electrode dosage of 100 g/L, SI:GAC mass ratio of 3:1, current density of 30 mA/cm², H₂O₂ dosage of 50 mmol/L, cathodic aeration of 0.8 L/min, and hydraulic retention time of 120 min. The average NB removal rate and chemical oxygen demand reached 67.38%±1.05% and 70.60%±1.15%, respectively, for which the increase in Fenton sludge was 891.8 mg/L. Different from the traditional Fenton process, additional Fe(II) was not required in the process used herein, reducing iron sludge accumulation and lowering the operating costs of using Fenton sludge as a hazardous waste treatment. In addition, the process applied in this study was able to reduce the chemical amounts used and increase the treatment efficiency. The reductions in sludge treatment costs and secondary pollutants make the proposed process an efficient and sustainable alternative for treating NB wastewater.