Evaluation of a pilot system for removal of the herbicide 2,4-dichlorophenoxyacetic acid and absorbance determination after clarification and adsorption on granular activated carbon

Abstract

The herbicide 2,4-dichlorophenoxyacetic acid (2,4-D) has been detected in water bodies worldwide, precluding their use for water supply. Despite this, scientific studies assessing the behavior of herbicides in water treatment systems are scarce, which motivated this study on 2,4-D removal. 2,4-D removal and its relationship with absorbance were investigated using a pilot system comprising coagulation, sedimentation, filtration, granular activated carbon (GAC) adsorption, and chlorinated disinfection. 2,4-D removal ranged from 15 to 64% after sedimentation, from negative values to 19% after filtration, and from 5 to 16% after chlorination, with total removal rates of 19 to 70%. Breakthrough curves showed an adsorption capacity of 0.70 mg g⁻¹ GAC for a C/C₀ ratio of 0.50 and a V_TW/V_GAC ratio of 3.598 for a breakthrough concentration of 30 ± 3 μg L⁻¹. The positive correlation between absorbance and 2,4-D (R² = 0.78) in the GAC column effluent indicated that absorbance can be used for early prediction of 2,4-D breakthrough. GAC column adsorption associated with coagulation produced treated water in accordance with the criteria for turbidity, apparent color, and 2,4-D concentration established by the Minister's Office/Ministry of Health — GM/MS Ordinance No. 888/2021, representing a promising technological alternative for 2,4-D removal from water treatment systems.

Keywords:
adsorption; activated carbon; 2,4-dichlorophenoxyacetic acid; pilot plant; water treatment