Equilibrium and kinetic studies on the adsorption of humic acid by activated sludge and Bacillus subtilis

This research is concerned with the adsorption of humic acid by activated sludge obtained from an alcoholic beverage plant and Bacillus subtilis (ATCC 6633). The effects of experimental factors such as initial pH, agitation speed, and types of adsorbent have been studied to compare adsorption capacity. The characterisation of activated sludge and Bacillus subtilis adsorption were examined by investigating the adsorption isotherm and kinetics. The results showed that the type of adsorbent had a significant relationship with adsorption capacity. In case of Bacillus subtilis, a maximum value of adsorption capacity of 11.44 mg humic acid /g biomass was observed based on the Langmuir adsorption isotherm and K value of 3.17× 10^-2 ((mg/g)(mg/l)ⁿ) from the Freundlich adsorption isotherm. The kinetic studies indicated that a pseudo second-order equation fitted the data remarkably well resulting in a rate constant (k₂) of about 0.019 g·mg-1min-1 for the adsorption onto Bacillus subtilis.