Conditions and Mechanisms in Thiocyanate Biodegradation

Abstract

Presence of thiocyanate (SCN–) is a problem of considerable interest in many industrial wastewaters, where this contaminant often appears accompanied by secondary sources of carbon, nitrogen and/or sulphur. In order to understand the effect of these compounds on the biodegradability of SCN–, this work investigates how the bacterium Pararacoccus thiocyanatus utilises the three elements that form the molecule of thiocyanate and compare this behaviour with those obtained in presence of other sources of N, S and C. Result showed that the bacterium was capable of utilizing thiocyanate as the sole substrate, achieving specific biodegradation rates of approximate 1.20 mg SCN– (mg cell·h)–1 and eliminating initial thiocyanate concentrations up to 5,000 mg L–1. Experimental data were successfully fitted to a Teisser model, assuming the existence of substrate inhibition obtaining values of μmax of 0.059 h–1, Ks of 790 mg L–1 and Ki of 6,520 mg L–1 for free mineral medium. Presence of additional carbon and nitrogen sources implied catabolic repression of the biodegradation of thiocyanate. In this case, only concentrations lower than 3,500 mg L–1 could be treated, obtaining specific degradation rates of around 0.70 mg SCN–·(h·mg cell)–1. Tessier model values showed a higher maximum specific growth rate (0.344 h–1), changing also the values for affinity and inhibition constants (1,150 mg L–1 and 1,730 mg L–1, respectively).