Sulfamethoxazole Removal from Drinking Water by Activated Carbon: Kinetics and Diffusion Process

Abstract

Sulfamethoxazole (SMX), a pharmaceutical residue, which is persistent and mobile in soils, shows low biodegradability, and is frequently found in the different aquatic compartments, can be found at very low concentrations in water intended for human consumption. In conditions compatible with industrial practices, the kinetic reactivity and performance of tap water purification using activated carbon powder (ACP) are examined here using two extreme mass ratios of SMX to ACP: 2 µg/L and 2 mg/L of SMX for only 10 mg/L of ACP. In response to surface chemistry, ACP texture and the intrinsic properties of SMX in water at a pH of 8.1, four kinetic models, and two monosolute equilibrium models showed a total purification of the 2 µg/L of SMX, the presence of energetic heterogeneity of surface adsorption of ACP, rapid kinetics compatible with the residence times of industrial water treatment processes, and kinetics affected by intraparticle diffusion. The adsorption mechanisms proposed are physical mechanisms based mainly on π-π dispersion interactions and electrostatic interactions by SMX^-/Divalent cation/ArO^- and SMX^-/Divalent cation/ArCOO^- bridging. Adsorption in tap water, also an innovative element of this study, shows that ACP is very efficient for the purification of very slightly polluted water.

Keywords: activated carbon; diffusion; kinetic; micropollutants; pharmaceuticals; sulfamethoxazole; wastewater; water treatment.

Figure 1

Sulfamethoxazole (SMX) speciation as a function of pH in aqueous solution.

Figure 2

Pore size distribution obtained by N₂ desorption at 77 K and CO₂ adsorption at 273 K.

Figure 3

SMX adsorption isotherm on ACP Norit SA Super at pH 8.1 in tap water solution.

Figure 4

Dimensionless concentration as a function of time for SMX adsorption by ACP in drinking water at 293 K. (Values given at ± 2 ng/L for 2 µg SMX/10 mg ACP and at ± 0.03 mg/L for 10 mg SMX/10 mg ACP).

Figure 5

Weber–Morris plots for the sorption of SMX by ACP Norit SA Super in drinking water. (SMX: 2 µg/L; ACP: 10 mg/L; pH = 8.1, T = 293 K).

Figure 6

Weber–Morris plots for the sorption of SMX by ACP Norit SA Super in drinking water. (SMX: 2 mg/L; ACP: 10 mg/L; pH = 8.1, T = 293 K).

Figure 7

Comparison of adsorption kinetic models at 293 K for 2 µg/L of SMX and 10 mg/L of ACP Norit SA Super in drinking water.

Figure 8

Comparison of adsorption kinetic models at 293 K for 2 mg/L of SMX and 10 mg/L of ACP Norit SA Super in drinking water.

Figure 9

Modeling of the adsorption kinetics of 2 µg/L of SMX per part.