BIOLOGICAL TREATMENT OF A SYNTHETIC GOLD MILLING EFFLUENT

This paper reports on biological sludge acclimatisation and the result s concerning the removal of free cyanide, thiocyanate and metallocyani des (copper, iron and zinc) from a synthetic gold milling effluent. Th e experiments were carried out in a continuous bench-scale bioreactor, and the experimental set-up consisted of two identical units, one of which served as control. The acclimatisation of the biomass was based on a stepwise procedure, in which the proportion of synthetic solution in the influent was gradually increased. The reactors were fed with a mixture of synthetic effluent and sewage, and the treatment efficienc y was evaluated through the monitoring of the following parameters: ch emical oxygen demand (COD), free cyanide, thiocyanate, copper, iron an d zinc concentrations. A well adapted microbial consortium was obtaine d at the end of the acclimatisation period, which was able to remove m ore than 95% of free cyanide, thiocyanate, copper and zinc, originally found in the influent. These removal efficiencies were obtained when the reactor was operated with a hydraulic retention time (HRT) of abou t 8 h. The performance results of experiments carried out with lower H RT (5 h) and higher dissolved oxygen (DO) concentration (6.5 mg litre( -1)) are also presented and discussed in this study.