Cyanate Degradation in Different Matrices Using Heat-Purified Enzymes

Abstract

A green and low-cost removal method for cyanate, a toxic byproduct from the treatment of cyanide, is still needed. Cyanase converts cyanate to CO2 and NH3, but its industrial practicality is limited because the reaction requires HCO3− as a substrate. In this study, we used carbonic anhydrase from Sulfurihydrogenibium azorense (SazCA) to provide HCO3− for cyanase from Thermomyces lanuginosus (TlCyn); both TlCyn and SazCA were purified by one-step heating without prior cell lysis. The heat treatment resulted in higher activities of both enzymes than the conventional two-step process. From a 50 mL-culture, the highest total activity of 147 U and 47,174 WAU was obtained from 5 min of heating at 60 and 80 °C for TlCyn and SazCA, respectively. The coupled enzymatic system was used to degrade cyanate in three different matrices: 50 mM Tris-HCl (pH 8), industrial wastewater, and artificial wastewater. In the industrial wastewater, with the addition of 0.75 WAU (Wilbur-Anderson unit) of SazCA, cyanate degradation using 0.5 mM NaHCO3 was similar to that using 3 mM NaHCO3, indicating an 83% reduction in NaHCO3. We have demonstrated that the dependence on HCO3− of cyanate degradation can be effectively alleviated by using low-cost heat-purified TlCyn and SazCA; the industrial practicality of the coupled enzymatic system is therefore improved.