Biodetoxification of cyanide-containing industrial wastewaters by Rhodococcus UKMP-5M

Abstract

The utilization of cyanide in many industrial processes despite its toxicity generated voluminous effluents, which necessitated treatment prior to discharge into the environment. In the present study, Rhodococcus UKMP-5M was solely employed as biological tool to detoxify three different cyanide-containing industrial wastewaters with different characteristics since initial attempt to employ mixed culture of Rhodococcus strains was unsuccessful due to synergistic interaction which yielded only 19% biodetoxification of 12 mM cyanide. The bacterium was able to achieve 97% cyanide removal efficiency in Wastewater A (pH 8.4) after 19 days of incubation. However, the growing cells needed the supplementation of nutrients, which was uneconomical besides requiring extensive time for complete detoxification. In contrast, the employment of immobilized beads of Rhodococcus UKMP-5M, which required a relatively straightforward method, were cost-effective in detoxifying almost 100% of 15 mM cyanide in Wastewater C (pH 9.5) within a short period of 3 days of incubation. This discovery is highly significant since most wastewaters pHs originating from various industrial applications involving cyanide often range from 6 to 9.5 and this strain is therefore seemingly effective for biodetoxification of cyanide-containing wastewaters with high pH values. In addition, it is interesting to note that the presence of heavy metals in the wastewaters did not inhibit the cyanide-degrading activity of the bacterium. The findings from this study provided essential information to develop a pilot plant on a technical scale for the biotreatment of industrial effluents bearing cyanide, which should be of great interest from an environmental and economic point of views.