Effectiveness of a simple biomixture for the adsorption and elimination of 2,4-dichlorophenoxyacetic acid (2,4-D) herbicide and its metabolite, 2,4-dichlorophenol (2,4-DCP), for a biobed system

Abstract

The remediation of point-source contamination of herbicides in productive fields can be addressed with biopurification systems which require biomixtures of natural materials with effectiveness for the adsorption and degradation of such compounds. A biomixture of wheat stubble and soil was tested for the adsorption and degradation of the herbicide 2,4-dichlorophenoxyacetic acid (2,4-D) and one of its main metabolites, 2,4-dichlorophenol (2,4-DCP). Single-contaminant kinetic studies were performed, being the pseudo-second order kinetic model the most suitable to describe the adsorption of both compounds. Although the adsorption of 2,4-D was faster, the adsorption of 2,4-DCP was three times higher. Single and competitive adsorption isotherms were also obtained. The later were acquired from a complete factorial experimental design varying the concentration of both solutes. Mathematical models were applied to describe the single solute isotherms, given a maximum monolayer adsorption capacity of 155.7 mg kg−1 for 2,4-D and 371.6 mg kg−1 for 2,4-DCP. Multicomponent models for bi-solute isotherms showed a clear reduction of 2,4-D adsorption in the presence of 2,4-DCP, although no adsorption displacement for the 2,4 DCP metabolite was observed. A stagnant degradation study was run and the contaminants were surveyed during 30 days. The biomixture was successful in degrading the 2,4-D, with a removal effectiveness > 96% after 15 days. The 2,4-DCP was not detected, suggesting a very fast degradation as soon as generated.