Biodegradation of cyanide in cassava wastewater using a novel thermodynamically-stable immobilized rhodanese.

Extracellular rhodanese obtained from Aureobasidium pullulans was employed in both free and immobilized forms for the biodegradation of cyanide present in cassava processing mill effluent (CPME). Crosslinking with glutaraldehyde (at an optimum concentration of 5% v/v) before entrapment in alginate beads resulted in the highest immobilization yield of 94.5% and reduced enzyme leakage of 1.8%. Rhodanese immobilized by cross-linking before entrapment (cbe) retained about 46% of its initial activity after eight cycles of catalysis compared to the entrapment in alginate alone (eaa) which lost more than 79% after the fifth catalytic cycle. A cross-examination of thermodynamic (ΔGd*, ΔSd*, ΔHd*) kinetic (kd, t1/2, D and z-values) parameters at 30-70 °C showed that cbe displayed a higher resistance to thermal inactivation when compared to the free enzyme (fe) and (eaa). The efficiency of cyanide biodegradation from the CPME by the fe, eaa and cbe were 55, 62, and 74% respectively after 6 h. Rhodanese immobilized via cbe had a higher resistance to thermal denaturation over other enzyme forms. Hence, this makes cbe adaptable for large-scale detoxification of cyanide from CPME.