In the present study, six gravity filters were constructed and evaluated for the treatment of agricultural wastewater contaminated with herbicide fluometuron. Two filter types in terms of feeding strategy (i.e., batch and continuous feeding strategies), three porous media (i.e., coarse gravel, coarse zeolite and fine zeolite) and three hydraulic residence times (i.e., 1 day, 2 days and 4 days) were evaluated to find the best design and operation parameter in fluometuron removal by adsorption on porous media. Batch experiments were also conducted and the experimental data were fitted to adsorption kinetic and isotherm models. Results showed that the experimental data fitted better to the pseudo-first order model and to the Freundlich model, and the highest fluometuron adsorption was recorded for fine zeolite. The results of filter operation indicated that the most important parameter affecting fluometuron removal is the hydraulic residence time.

Six gravity filters were constructed and evaluated for the treatment of water contaminated with herbicide fluometuron. Two filter types in terms of feeding strategy (i.e., batch and continuous feeding strategies), three porous media (i.e., coarse gravel (CG), coarse zeolite (CZ) and fine zeolite (FZ)), and three hydraulic residence times (i.e., 1 day, 2 days and 4 days) were evaluated to find the best design and operation parameter in fluometuron removal by adsorption on the porous media. Batch experiments were also conducted and the experimental data were fitted to adsorption kinetic and isotherm models. Results showed that the experimental data fitted better to the pseudo-first-order model for the three porous media tested and the ranking order of the fluometuron adsorption capacities was FZ>CZ>CG. The results also showed that fluometuron adsorption capacities were better fitted to the Freundlich model for both CZ and FZ porous media, and in all cases, the 1/n value was less than 1 indicating that fluometuron adsorption on both media is a favorable physical process. According to the Freundlich model, the highest fluometuron adsorption was recorded for fine zeolite (2.29 mg/kg). The results of filter operation indicated that the FZ unit with continuous feeding strategy at HRT of 2 days and 4 days achieved the highest fluometuron removal (34.2%) and that the most important parameter affecting fluometuron removal is the hydraulic residence time. KeywordsPesticides • Hydraulic residence time • Gravity filters • Adsorption kinetic models • Freundlich and Langmuir isotherms Highlights • Batch and continuous gravity filters are used to remove fluometuron • Kinetic and isotherm models on fluometuron adsorption are presented • Adsorption on the porous media was the main process of herbicide removal • The hydraulic residence time (HRT) of 4 days was adequate for fluometuron removal • The FZ-C unit at HRT of 2 and 4 days showed the highest removal capacity * Zisis Vryzas