IMPROVEMENT OF HEAVY-METAL BIOSORPTION BY MYCELIAL DEAD BIOMASSES (RHIZOPUS-ARRHIZUS, MUCOR-MIEHEI AND PENICILLIUM-CHRYSOGENUM) - PH CONTROL AND CATIONIC ACTIVATION

Fungal mycelial by-products from fermentation industries present a con siderable affinity for soluble metal ions (e.g. Zn, Cd, Ni, Pb, Cr, Ag ) and could be used in biosorption processes for purification of conta minated effluents. In this work the influence of pH on sorption parame ters is characterized by measuring the isotherms of five heavy metals (Ni, Zn, Cd, Ag and Pb) with Rhizopus arrhizus biomass under pH-contro lled conditions. The maximum sorption capacity for lead was observed a t pH 7.0 (200 mg g(-1)), while silver uptake was weakly affected. The stability of metal-biosorbent complexes is regularly enhanced by pH ne utralization, except for lead. A transition in sorption mechanism was observed above pH 6.0. In addition, comparison of various industrial f ungal biomasses (R. arrhizus, Mucor miehei and Penicillium chrysogenum ) indicated important variations in zinc-binding and buffering propert ies (0.24, 0.08 and 0.05 mmol g(-1), respectively). Without control, t he equilibrium pH (5.8, 3.9 and 4.0) is shown to be related to the ini tial calcium content of the biosorbent. pH neutralization during metal adsorption increases zinc sorption in all fungi (0.57, 0.52 and 0.33 mmol g(-1)) but an improvement was also obtained (0.34, 0.33 and 0.10 mmol g(-1)) by calcium saturation of the biomass before heavy metal ac cumulation. Breakthrough curves of fixed bed biosorbent columns demons trated the capacity of the biosorbent process to purify zinc and lead solutions in continuous-flow systems, and confirmed the necessity for cationic activation of the biosorbent before contact with the heavy-me tal solution.