Biological treatment of cyanides, with and without sewage

In experiments in which potassium cyanide or complex metal cyanides were added to sewage being treated in laboratory-scale percolating filters, it was shown that, after causing a slight initial depression in oxidation of ammonia to nitrate, a concentration in any of the cyanides used of up to an equivalent of 4 p.p.m. of HCN had no further detectable effect on purification of the sewage, and that 99–100% of the cyanide was destroyed in the filters. In filters acclimatized to cyanide, more than 99% of the cyanide was destroyed in solutions in sewage or in water containing at least 100 p.p.m. of HCN as potassium cyanide or the complexes of zinc or cadmium, and more than 75% was destroyed in similar solutions of the complexes of copper or nickel. The action appears to be biological, and may offer an alternative to chemical treatment for removal of cyanide from industrial waste waters.