Development of a process for biodetoxification of metal cyanides from waste waters

A bacterial consortium capable of utilising metal cyanides as a source of n itrogen was used to develop a microbiological process for the detoxificatio n of metal cyanides (viz. copper cyanide and zinc cyanide) from electroplat ing waste water. Optimal conditions biodegradation of both the metal-cyanid e compounds were pH 7.5, temperature 35 degrees C, inoculum size 10(9) cell s per mi and glucose or sugarcane molasses requirement of 5 mM or 0.6 ml/l, respectively. Metal precipitates obtained during metal-cyanide biodegradat ion were identified as metal-hydroxides. When the treatment was carried out in a 27 1 rotating biological contactor (RBC) in continuous mode, the syst em could achieve > 99.9% removal of 0.5 mM metal cyanide (ca. 52 mg/l cyani de and 30-40 mg/l copper/zinc) in 15 h with sugarcane molasses as carbon so urce. The RBC treated effluent was found to be safe for discharge in the en vironment as confirmed by chemical analysis and fish bioassay studies. (C) 2000 Elsevier Science Ltd. All rights reserved.