Synergic effect of adsorption and biodegradation enhance cyanide removal by immobilized Alcaligenes sp. strain DN25.

A high efficiency and stability polyurethane-foam (PUF)-immobilized cell system was constructed to remove cyanide based on simultaneous adsorption and biodegradation (SAB). The performance of the PUF-immobilized system was evaluated by comparison with the freely suspended cell system. The SAB system exhibited more effective and robust, and could still remain degradation activity even at 40 °C or pH 11.0. The SAB system completely removed 500 mg CN-/L within 8 h at 30 °C, pH 8.0, and 120 rpm, whereas 12 h were required for the free cells system. Moreover, the SAB system showed apparent superiority in removing higher concentration cyanide up to 1200 mg CN-/L. A continuously stirred tank bioreactor (CSTR) was successfully designed and steadily operated with approximately 85% of the total average removal efficiency for 52 days at an influent cyanide concentration of 100-200 mg/L, which demonstrated a favorable reliability. Cyanide removal process could be well described using a pseudo first-order model, and the higher apparent rate constants (k) of the immobilized cells showed the synergic effect of adsorption and biodegradation significantly enhanced cyanide removal. Preliminarily, it was found that the foam characteristic might play a not negligible role on the cyanide-degrading enzyme expression of strain DN25 in the SAB system.