Control of chironomid larvae growth and inactivation mechanisms by UV/ClO2: efficacy and pathways

Abstract

Chironomid larvae, as typical freshwater benthic organisms, have become significant biological pollutants in the front-end of drinking water systems in water-scarce regions due to their strong environmental adaptability. This study investigates risk control strategies for chironomid larvae proliferation in drinking water systems using two approaches: water quality parameter regulation and efficient inactivation technology. Single-factor and orthogonal experiments revealed that the optimal growth conditions for chironomid larvae are 20 °C, pH = 6, and COD_Mn = 2 mg L⁻¹. Within a turbidity range of 10–20 NTU, both survival and pupation rates were relatively high, whereas excessive turbidity (60 NTU) significantly reduced these rates. Consequently, a proliferation early-warning mechanism was proposed, using turbidity as the core indicator combined with water temperature and COD_Mn monitoring. The efficacy of UV, ClO₂, and UV/ClO₂ combined systems for chironomid larvae inactivation was systematically compared. The results demonstrated that the UV/ClO₂ combined treatment exhibited a distinctive three-phase inactivation pattern (lag–rapid–tail), showing significantly superior performance compared to individual treatments. Notably, pretreatment with 2 hour UV irradiation followed by 7.0 mg L⁻¹ ClO₂ achieved 100% inactivation within 7 hours (total UV radiation dose: 1.934 J cm⁻²), significantly improving inactivation efficiency. This study pioneers the application of a combined ultraviolet/chlorine dioxide disinfection system, achieving highly efficient inactivation of chironomid larvae. From a technical perspective, the optimization of process parameters and the introduction of pretreatment strategies have significantly improved treatment efficiency, while providing experimental evidence and methodological support for subsequent system monitoring and control. From a mechanistic perspective, the innovative integration of biological transmission electron microscopy with antioxidant enzyme system analysis has elucidated the operational principle of induced oxidative stress leading to organismal damage. The research revealed two key pathways for UV/ClO₂ synergistic inactivation: (1) contact-killing effect: ClO₂ penetrates the larval cuticle to directly damage cellular organelles and nuclei, while UV co-treatment exacerbates cuticle damage and enhances ClO₂ penetration, accelerating cellular structure disintegration. (2) Oxidative stress enhancement: UV irradiation amplifies ClO₂-induced oxidative stress, generating reactive species that disrupt metabolic functions and overwhelm the antioxidant system, ultimately impairing the larvae's normal physiological functions. This study provides a novel and efficient strategy for the prevention and control of chironomid larvae in drinking water systems.