Degradation of highly chlorinated pesticide, lindane, in water using UV/persulfate: kinetics and mechanism, toxicity evaluation, and synergism by H2O2

Highlights: • Degradation of lindane by UV/persulfate based AOPs was investigated. • Mechanism involved H-abstraction by SO₄^{• −} accompanied by C-Cl bond cleavage via UV-C. • Both less and more toxic by-products than lindane were produced, but vanished at high UV dose. • Natural organic matter and inorganic ions considerably affect degradation efficiency. • H₂O₂ had significant synergistic effects on UV/persulfate process. Sulfate radical-advanced oxidation processes (SR-AOPs) are emerging technologies for decomposing organic pollutants in water. This study investigated the efficiency of UV/persulfate (UV/S₂O₈²⁻) process to degrade lindane in water, showing 93.2% lindane removal ([lindane]₀ = 3.43 μM, [S₂O₈²⁻]₀ = 100 μM) at a UV fluence of 720 mJ/cm². The lindane degradation followed first order kinetics and mechanistic studies suggested H-abstraction by SO₄^{• −} and Cl removal via C-Cl bond cleavage by UV-C light. Toxicity assessment using ECOSAR program showed toxicity gradually decreased and eventually no significant toxicity remained when all by-products vanished at high UV dose. Removal efficiency of lindane decreased from 93.2% to 38.4, 45.5, 56.0, 84.3 and 88.6%, by adding 1.0 mg/L humic acid or 1.0 mM CO₃²⁻, HCO₃⁻, Cl⁻ or SO₄²⁻, respectively. Coupling of H₂O₂ with UV/S₂O₈²⁻ showed a significant synergistic effect with 99.0% lindane removal at a UV fluence of 600 mJ/cm², using [S₂O₈²⁻]₀ = [H₂O₂]₀ = 50 μM while UV/H₂O₂ resulted in only 36.6% lindane removal ([lindane]₀ = 3.43 μM, [H₂O₂]₀ = 100 μM) at a UV fluence of 720 mJ/cm². The results indicate that SR-AOP has potential for consideration as a remedial technology to treat persistent chlorinated pesticides such as lindane in contaminated water.