Thiocyanate removal from saline CIP process water by a rotating biologicalcontactor, with reuse of the water for bioleaching

Two strains of bacteria that were known to be capable of degrading thiocyan ate were isolated from the Youanmi gold mine in Western Australia. Both str ains demonstrated the ability to utilise thiocyanate as their sole energy a nd nitrogen source. Physiological characterisation indicated that both stra ins had the potential to tolerate the variable conditions encountered in Yo uanmi tailings water. Phylogenetic analysis showed that the strains were ei ther members of the genus Thiobacillus or Halomonas but could not be accomm odated within any existing described species. Phosphate was the only additi onal nutrient required. Both strains were inoculated into a laboratory-scale rotating biological co ntactor, where degradation took place in saline, low-nutrient water. The bi omass supported on the reactor surface (20 m(2)) was capable of degrading a pproximately 2800 mg thiocyanate L-1 to less than 1 mg L-1 at a flow rate o f 30 mL min (-1) and a hydraulic retention time of 11.1 h. When this degrad ed water was used as the basal medium for testing the bacterial oxidation o f ferrous ion and of arsenopyrite and pyrite, the rates obtained were simil ar to those obtained with thiocyanate-free medium. This showed that degrada tion was successful, that the by-products of the reaction, ammonium and sul phate ions and carbon dioxide, were not toxic to iron- and sulphide-oxidisi ng bacteria, and that water could be recycled to a biological oxidation pla nt after passage through the thiocyanate-degrading reactor. (C) 2001 Elsevi er Science B.V. All rights reserved.