Determining an effective operating window for a thiocyanate-degrading mixed microbial community

Thiocyanate-laden effluents are generated during the cyanidation stage of gold production. Thiocyanate (SCN−) is difficult to remove using conventional treatment processes. Biological alternatives, such as the activated sludge tailings effluent remediation (ASTER™) process have been developed to treat thiocyanate and cyanide laden process water, but their application has been limited. Driven by the desire to broaden the commercial application of the technology, research was conducted to define the effective operating window with respect to pH, temperature and thiocyanate concentration. Biodegradation of SCN− by the mixed microbial community was assessed in batch experiments at an initial SCN− concentration of up to 1800 mg/L. A concentration dependent period of apparent inactivity was observed when the unacclimitized stock culture was exposed to elevated SCN−. Exposure to elevated SCN− levels induced floc formation, presumably as a stress response. The effect of temperature, across a range from 10 to 45 °C, was assessed at SCN− concentrations between 60 and 180 mg/L, with optimum degradation occurring between 30° C and 40 °C. The effect of solution pH on SCN−degradation was investigated between pH 5.0-10.0, with optimum performance at pH 7.0. A significant decrease in degradation rates was observed below pH 6.5 and above pH 8.5. This research has helped to establish an effective operating window for the ASTER™ process.