Removal of 2,4-Dichlorophenoxyacetic acid from water and organic by-product minimization by catalytic ozonation

Abstract

Background: 2,4-dichlorophenoxyacetic acid (2,4-DCPA acid) is a toxic herbicide. Earlier studies to remove 2,4-DCPA acid from water used expensive and/or toxic reagents, resulting in the formation of toxic organic by-products (Org-BPs). This study evaluates the removal of 2,4-DCPA acid from aqueous media using uncatalysed and catalytic ozonation with Fe doped with Ni and Co respectively. Methods: Mixed metal oxides of Ni and Co loaded on Fe respectively, prepared by co-precipitation and physical mixing were used as catalyst for ozone facilitated oxidation degradation of 2,4-DCPA acid. Their surface properties were determined by employing SEM, BET and NH3-TPD. HPLC, IC and TOC data were used for quantifying substrate and oxidation products. Results: Conversion of 2,4-DCPA acid increased from 38% in acidic water to 73% in basic water, however, only 26% of the total carbon was removed and 9.5% in the form of Org-BPs. With 7:3 Fe:Ni (Co-ppt) catalyst (surface area 253 m2 g-1; particle size 236 nm), 97% of pollutant was converted. Most importantly, 92% of carbon was removed and Org-BP formation was minimized to 1.5%. With 7:3 Fe:Ni (Mixed) catalyst (surface area 12 m2 g-1; particle size 1274 nm), 68% of 2,4-DCPA acid was converted, while 23% of TOC was removed, however, 66% of Org-BP's still remained. Conclusion: In uncatalysed ozonation degradation of 2,4-DCPA acid improved with the increase in hydroxide ion concentration. Ozonation in presence of 7:3 Fe:Ni (Co-ppt) catalyst resulted in highest activity for dechlorination, TOC removal and Org-BP minimization, thus improving the quality of contaminated water.