Effective degradation of carbofuran and organophosphate pesticides via a continuous-flow, visible-light-activated periodate oxidation system using floatable, sodium alginate/water lettuce-derived biochar/hollow glass microspheres

Abstract

This study presents the synthesis of floatable sodium alginate/water lettuce-derived biochar/hollow glass microsphere (SA/WLBC/HGM) beads and their application as activators of periodate (PI) for the degradation of carbofuran (CBF) in a continuous-flow packed-bed photoreactor. The degradation mechanisms and the optimization of continuous-flow photoreactor systems remain insufficiently explored in the existing literature. Under the optimized conditions (catalyst dosage of 4 g, PI concentration of 0.8 g L⁻¹, flow rate of 2 mL min⁻¹, reaction time of 200 min, neutral pH, and ambient temperature), the SA/WLBC/HGMs–PI/light system achieved a CBF degradation efficiency of 94.11%. Under the same conditions, degradation efficiencies of 89.77, 84.50, and 78.12% were obtained for diazinon, malathion, and chlorpyrifos, respectively. Singlet oxygen species were the main contributors to the degradation process, and the degradation mechanism was explored. Toxic iodinated byproducts were not detected in the SA/WLBC/HGMs–PI/light degradation system, and most of the generated intermediates were less toxic compared to CBF. The SA/WLBC/HGMs beads demonstrated high stability under five successive cycles with a total loss of 1.86% in degradation efficiency. The degradation performance was evaluated in the presence of inorganic ions, natural organic matter, and different water matrices. Techno-economic analysis demonstrated the economic feasibility of the treatment system for mixed-pesticide wastewater, as evidenced by a relatively short payback period of 5.5 years, a positive net present value, and a profitability index exceeding unity. This study presents a stable, efficient, and inexpensive continuous-flow packed-bed photoreactor that can be employed for the remediation of real-world industrial effluents.