Commercial herbicide degradation by solar corrosion Fenton processes of iron filaments in a continuous flow reactor and its computational fluid dynamics (CFD) simulation

Commercial solutions of paraquat (PQ) herbicide were treated by solar corrosion Fenton processes (SCF). A borosilicate reactor was packed with a coiled filament of annealed iron wire to different reactor volume/filament surface area ratios (V_t/A_f). A cylindrical parabolic concentrator was designed to concentrate UV light. The response surface methodology was used to determine the optimal process conditions using a Box-Behnken design in the removal of PQ, COD, and TOC. The independent variables used in this study were: H₂O₂ concentration (500, 1500, and 2500 mg L⁻¹), hydraulic retention time (HRT) (20, 30, and 40 min), and V_t/A_f (3:1, 6:1 and 9:1 cm³: cm²). Solution pH was adjusted to 2.8. The optimal conditions for the removal of PQ were: 2248.7 mg L⁻¹ of H₂O₂, an HTR of 28 min, and V_t/A_f of 3.4:1. These yielded a 99.9 % removal of PQ, 100 % removal of COD, and 96.7 % of TOC. Toxicity was 100 % removed with 700 mg L⁻¹ of H₂O₂. CFD indicated operating fluid velocity and turbulence contributed to maintaining an adequate Fe^{2 +}.