Enhanced degradation of lindane in water by sulfite-assisted ultrasonic (SF/US) process: The critical role of generated aqueous electrons.

Persistent pesticides pose significant environmental and health risks due to their strong resistance to conventional degradation methods. This study investigates the degradation of lindane (LND), a perchlorinated pesticide, using a sulfite-assisted ultrasonic (SF/US) process, focusing on the critical role of aqueous electrons (e) in reductive dechlorination. Aqueous electrons were indirectly identified as the primary reactive species in the SF/US system for pollutant degradation, providing insights into US-induced reduction mechanisms. The SF/US system significantly enhanced LND removal, achieving 99.4 % ± 1.0 % degradation within 100 min, compared to 88.9 % ± 1.5 % under ultrasound alone. Kinetic analysis showed that sulfite addition nearly doubled the reaction rate constant (from 0.022 to 0.041 min), confirming that e drive LND degradation more efficiently than hydroxyl radicals (HO). Scavenging experiments further demonstrated that nitrate strongly inhibited degradation, while tert-butanol (TBA) had minimal effect, verifying that e, rather than HO, dominate the process. The efficiency of SF/US was influenced by various factors, with optimal removal achieved at 200 kHz, oxygen-depleted conditions, and pH 10. The degradation pathway primarily involved sequential reductive dechlorination of LND, progressing through pentachlorocyclohexene, tetrachlorocyclohexadiene, and trichlorobenzene intermediates before ultimately forming non-toxic aromatic derivatives such as hydroquinone and phenol. These findings highlight SF/US as a novel and highly efficient strategy for the remediation of chlorinated pesticides in water treatment.