Characterization of sulfamethoxazole biosorption by Rhizopus oryzae biomass: Insights into sorption mechanism

The occurrence of antibiotics in some environmental compartments is a global concern. Sulfamethoxazole (SMX) is one of the most widely used antibiotics worldwide and is commonly found in the environment. In this paper, the effect of pH and lipids on SMX sorption by the fungal biomass of Rhizopus oryzae was studied. SMX biosorption was characterized by FTIR, kinetic, equilibrium, and thermodynamic studies. The greatest SMX adsorption capacity was found at pH 4.0. Under optimal pH, the adsorption rate of SMX was mostly controlled by intraparticle diffusion. The pseudo-first-order model (qe = 252.72 μg g−1, k1 = 0.099 h−1) and the linear isotherm (Kd = 0.211 L g−1) successfully modeled the kinetic and equilibrium data (R2 > 0.97). Moreover, at equilibrium, the absence of lipids in biomass led to a decrease of 2.98-fold in the adsorption capacity for SMX, from 0.211 to 0.071 L g−1, demonstrating that lipids are mainly responsible for removal. Some functional groups from proteins and chitin/chitosan were also identified as potential adsorption sites. Biosorption of SMX was a spontaneous phenomenon (ΔG0 from −13.269 to −14.996 kJ mol−1) with endothermic nature (ΔH0 = 17.595 kJ mol−1), driven by weak ionic and hydrophobic interactions. According to our results, the SMX sorption by R. oryzae biomass can be attributed to both adsorption on the biomass surface and absorption in lipids.