Removal of humic acid fractions by Rhizopus arrhizus: Uptake and kinetic studies

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Abstract
Humic acid components HFO‐A and HPI‐N were studied for their removal by Rhizopus arrhizus. The removal was stimulated by the presence of sucrose followed by pretreating biomass with formaldehyde or autoclaving. The presence of Cd2+ ions and high ionic strength in solution was found to increase the adsorptive capacity of R. arrhizus for HPO‐A and HPI‐N. The uptake of HPO‐A and HPI‐N by R. arrhizus was biphasic in nature and generally a much slower process than heavy metal biosorption. The first phase was rapid and independent of metabolic energy while the second phase was slow and dependent on metabolic energy. The infrared spectra showed no chemical reaction has occurred between cell walls and adsorbates. Physical adsorption is therefore the main mechanism of humic removal by inactive R. arrhizus.