Abstract: A two-stage apparatus for the purification of cyanide-containing waste water allows relatively clean water to be obtained from waste water containing high concentrations of cyanide and solids in suspension. The apparatus in its first stage includes a bioreactor having a biocultivator (27) for cultivating microorganisms. A reservoir means (1) in communication with the cultivator (27) is provided for receiving and treating a mixture of waste water and microorganisms, having a downwardly converging conical base. Oxygenating means (8) are provided in a region proximate the conical base, for supplying oxygen to the mixture. Temperature regulating means (7) and stirring means in the form of a stirrer or pump (6) are also provided. The second stage of the apparatus comprises a sorption chamber (28) in communication with the reservoir means, for containing an ion-exchange resin, activated carbon, charcoal, or other sorption material.