Study on the Removal of Humic Acid from Road Tunnel Drainage Systems Based on Electric Field-Enhanced Co(II)-Mediated Peroxymonosulfate System

The issue of clogging in highway tunnel drainage systems primarily stems from the long-term accumulation of floc-like sediments formed by the chelation of natural organic matter with metal ions. This study employed an electric field-enhanced Co(II)-mediated peroxymonosulfate system (E/Co(II)/PMS) for the efficient treatment of humic acid. Compared with the E/Co(II), Co(II)/PMS, or E/PMS systems alone, the E/Co(II)/PMS system exhibited superior humic acid removal performance, with a degradation rate of 92.3% in 30 min, which significantly improved the oxidation efficiency. The study reveals the mechanism of Co(II) activation of PMS to generate sulfate radicals (SO4•–) and hydroxyl radicals (HO•), and maintains the reaction in a sustained and efficient manner by cathode-driven Co(III)/Co(II) cycling. The experimental results showed that pH = 7, 0.2 mM Co(II), and 17 mA/cm2 current density were the optimal parameter combinations, and the degradation was inhibited by the inorganic anion CO32–, PO43–, and Cl–, which increased with its concentration, with the strongest inhibitory effect being observed for Cl–. The present study not only provides an efficient technical solution to address the issue of organic clogging in tunnel drainage systems, but also provides a theoretical and applied basis for the electrochemical oxidative degradation of organic pollutants in complex water quality through the analysis of the mechanism and optimization of the parameters.