Some industrial processes, such as plating and gold mining, utilise cyanide and related compounds in their operations. The resulting effluents contain cyanide, thiocyanate, and other toxic ions, which are noxious to the environment and require removal before effluent discharging. Several methods are available for cyanide removal and/or detoxification. Natural degradation, alkaline chlorination, and oxidation with hydrogen peroxide are the most frequently used methods in full-scale operations. However, there are technical and economical concerns related to these methods, which make biological treatment processes a feasible alternative. The use of a trickling filter is suitable for treating wastewaters with load variation. It is a simple system, is easy to operate, and presents low energy requirements. In this type of bioreactor, it is possible to retain microorganisms with a slow growth rate, such as those responsible for cyanide degradation. The present work reports the results obtained in a fixed bed bioreactor in which were evaluated: (a) the influence of the recirculation ratio (0 to 0.75), (b) the role of a biomass in cyanide removal, and (c) the biomass characteristics. The experiments were carried out in a continuous pilot scale trickling filter, 7.4 m high, packed with plastic rings of polypropylene. The experimental set-up consisted of two identical units, one of which was used for tests without biomass (abiotic tests). The reactors were fed with a mixture of synthetic gold milling effluent and sewage, and the treatment efficiency was evaluated through the monitoring of the following parameters: chemical oxygen demand (COD), free cyanide, thiocyanate, copper, iron and zinc concentrations. The results indicated that it was possible to remove more than 90% of the free cyanide, thiocyanate. copper and zinc originally found in the influent. These removal efficiencies were obtained when the pilot bioreactor was operated without recirculation, and moreover, higher recirculation ratio brought about a decreasing in the pH of the influent, lowering the efficiency of zinc removal. It was observed that the microbial activity was found to be responsible for thyocyanate degradation and copper removal. The tests carried out in the reactor without biomass showed that the percentage of free cyanide removed by volatilisation was low (22.6%), and even lower when recirculation did not take place (7.7%). This fact confirms the important role, which the biomass plays in the degradation of this pollutant.