Advanced oxidation process with hydrogen peroxide and sulfite for superfast degradation of micro-contaminants in drinking water

Sulfite (S(IV))-based advanced oxidation processes (AOPs) have recently gained attention as viable alternatives to peroxosulfate-based AOPs due to their low toxicity and cost-effectiveness. Hydrogen peroxide (H₂O₂) is widely recognized as an effective and environmentally friendly oxidant in drinking water treatment. This study introduces a novel H₂O₂/S(IV) AOP based on the observation of over-stoichiometric consumption of S(IV) by H₂O₂. This system generates a variety of reactive species (RSs), including sulfate radicals (SO₄^•-), hydroxyl radicals (•OH), superoxide anion radicals (O₂^•–), and singlet oxygen (¹O₂), to achieve rapid degradation of micro-contaminants in drinking water. With dosages of H₂O₂ and S(IV) set at 0.1 mM and 1.0 mM, respectively, the H₂O₂/S(IV) system generated concentrations of SO₄^•-, •OH, O₂^•– and ¹O₂ at approximately 10⁻¹², 10⁻¹², 10⁻¹³, and 10⁻¹³ M. This occurred even in complex water matrices containing bicarbonate (HCO₃^-), chloride (Cl^-), and humic acid (HA) across a pH range of 3.0–11.0. A kinetic model was developed to simulate RS generation and predict the pseudo-first-order degradation rate constants (k) for 15 micro-contaminants in the H₂O₂/S(IV) system. Theoretical calculations indicated that micro-contaminants with high E_HOMO and low ΔE (i.e., E_LUMO - E_HOMO) are more susceptible to degradation. Compared to UV/H₂O₂, UV/S(IV), Fe²⁺/H₂O₂, and Fe³⁺/S(IV) systems, the H₂O₂/S(IV) system demonstrated faster degradation rates, with k values 1–2 orders of magnitude higher, towards micro-contaminants. Additionally, the H₂O₂/S(IV) system was more effective in controlling disinfection by-product formation during subsequent chlorination, highlighting the application potential of the H₂O₂/S(IV) system in drinking water treatment.