Fenton’s Oxidation of Herbicides in Water

Abstract

The present study attempts the conventional Fenton’s process (CFP) and advance Fenton’s process (AFP) for the oxidation of herbicides (2,4-D, dicamba and ametryn) in actual agriculture runoff water and in aqueous medium. The degradation experiments were initiated with CFPs (FeSO4.7H2O as a precursor) and later the AFP (FeNPs synthesized from laterite and sustainable plant extract) was performed. Both RSM (response surface methodology) and Taguchi methods were applied for the design of experiments. The influence of H2O2/COD, H2O2/Fe 2+ pH and reaction time were studied on four responses (ametryn, 2,4-D, dicamba and COD removal efficiency). Agriculture runoff water and aqueous solution were successfully treated by CFPs with the removal efficiencies of 71-100% and 84.01-100% respectively. The whole oxidation process was monitored by LC/MS and COD. It was found that compounds were mineralized to oxalic acid, thiocynate ion and maleic acid for dicamba, ametryn and 2,4-D respectively with the release of chloride ion. The regression analysis was performed, in which coefficient of variation (<8), and adequate precision (>12) were in good agreement with model values. Finally, the treatment process was validated by performing the additional experiments. In AFPs the Fe nanoparticles were synthesized using Eucalyptus Globulus (EG)(Nilgiri) and Tactona Grandis (TG)(Teak) extracts. The low cost and locally available laterite was used as a source of iron rather than using iron salts. The raw laterite particles (RLPs) and synthesized green iron nanoparticles (GLFeNPs) were characterized using FESEM-EDX, XRD, FTIR, and BET techniques. The obtained results confirmed that 20-70 nm (EG) and 50-100nm (TG) of spherical FeNPs were formed (surface area of 31- 36.62 m2/g and pore volume of 0.038- 0.0394cm3/g) for TG and EG respectively. The XRD analysis shows that GLFeNPs consists of mainly Fe0, Fe2O3, Fe3O4 and polyphenols. Later, the GLFeNPs were applied as a Fenton-like catalyst and 100% removal of all herbicides was observed. The EG extract is showing higher polyphenols and antioxidant power than TG extract and the 1st order kinetic model was best fitted to the experimental data than the 2nd order (R2 >0.85). The AFP is working near to the neutral pH than CFP and more degradation efficiency was observed in AFP. Finally, the cost analysis for the synthesis of FeNPs was performed, which is less than the commercial grades and hence it can be recommended for the alternative novel catalyst for the oxidation studies.