Degradation of commercial paraquat in a solar-Fenton pilot lagoon using iron oxalate as a chelating agent: Hydro-thermal analysis with CFD

The performance of a solar Fenton in commercial paraquat (Gramoxone) was analyzed at natural pH with paraquat (PQ) concentrations of 0.9, 0.7 and 0.1 mM. This photochemical treatment was mediated by different concentrations of ferrioxalate and hydrogen peroxide in a solar pilot lagoon which was analyzed with CFD to verify its hydrodynamic and temperature performance. PQ degradation efficiencies of 51.93%, 91.55%, and 96.54% for PQ concentrations of 0.9, 0.7, and 0.1 mM, respectively, were achieved. COD reduction percentages of 61.23%, 82%, and 92% were observed after 8 h of hydraulic retention time. The maximum mineralization was 85.90%, 80.67%, and 94%, respectively. The following ratios were tested for 0.9, 0.7, and 0.1 mM PQ: oxalate/PQ = 2.5, 3.29 and 23; H₂O₂/PQ = 2.14, 2.74 and 19.18. The ratios of oxalate/Fe³⁺ = 20 and H₂O₂/Fe³⁺ = 16 were the best for the treatment of the three PQ concentrations. These conditions were highly effective for the treatment of this herbicide. To improve the reaction rate, it is necessary to increase the accumulative energy, which would reduce the treatment time.