Characteristics, kinetics and thermodynamics of Congo Red biosorption by activated sulfidogenic sludge from an aqueous solution

The kinetics and thermodynamics of the biosorption of textile dye Congo Red on anaerobic activated sulfidogenic sludge were examined. The influence of different adsorption parameters such as pH, temperature, contact time and initial dye concentrations on the biosorption capacity was also investigated. The sulfidogenic sludge showed a maximum biosorption density of 238.90 mg dye/g cell for Congo Red at an initial dye concentration of 1,000 mg/L, pH 3.5 and 22 °C, which is higher than that of many other adsorbents reported in the literature. The biosorption processes obeyed the Langmuir isotherm and exhibited pseudo-second-order rate kinetics. The thermodynamic parameters indicated the spontaneous and exothermic nature of Congo Red biosorption. The Fourier transform infrared spectra revealed the dye interaction with the biomass. Scanning electron microscopy showed significant changes in the surface morphology of the sludge after dye biosorption. These results showed that sulfidogenic sludge biomass is an attractive alternative low-cost biosorbent for the removal of the dye from aqueous media.