Removal of p-toluenesulfonic acid from wastewater using a filtration-enhanced electro-Fenton reactor

Abstract

Rapid global industrialization accompanies the discharge of industrial wastewater. p-Toluenesulfonic acid (PTSA), a kind of aromatic sulfonate that belongs to the refractory organic pollutant, is one of the most widely used chemicals in pharmaceutical, dye, petrochemical and plastic industries. In this study, we developed a filtration-enhanced electro-Fenton (FEEF) reactor to remove PTSA from synthetic wastewater. A filtration-enhanced stainless-steel mesh (FESSM) was used as the cathode. Under the optimal operating conditions of applied voltage 2.5 V, pH = 3.0, addition of 0.2 mM Fe²⁺ and 1.0 mM H₂O₂ for 120 min, the removal efficiency of PTSA (initial concentration of 100 mg L⁻¹) could reach 92.6%. Compared with the control anodic oxidation and conventional Fenton system, the FEEF system showed higher ˙OH yield and PTSA removal efficiency, with a lower effluent biological toxicity and operating cost. The enhanced mass transfer rate by the filtration in the FEEF system accelerated the regeneration of catalyst Fe²⁺ and further promoted the heterogeneous reactions. The Fe species on the surface of FESSM cathode possessed a gradient distribution, the inner layer was dominated by Fe and the outer layer was Fe³⁺. The degradation pathways of PTSA were proposed, including methyl hydroxylation, sulfonyl hydroxylation, β-hydrogen hydroxylation, and ring-opening reaction. These results demonstrate that the novel FEEF system is a promising technology for the removal of refractory organic pollutants from industrial wastewater.