Batch and continuous biooxidation of sulphide by Thiomicrospira sp. CVO: Reaction kinetics and stoichiometry

Aqueous phase biooxidation of sulphide by the novel sulphide-oxidizing bacterium Thiomicrospira sp. CVO was studied in batch and continuous systems. CVO was able to oxidize sulphide at concentrations as high as 19 mM. Sulphide biooxidation occurred in two distinct phases, one resulting in the formation of sulphur and possibly other dissolved sulphur compounds rather than sulphate, followed by sulphate formation. The specific growth rate of CVO in the first and second phases were 0.17–0.27 and 0.04–0.05 h−1, respectively. Nitrite accumulated in the culture during the first phase and was consumed during the second phase. The composition of end-products was influenced by the ratio of sulphide to nitrate initial concentrations. At a ratio of 0.28, sulphate represented 93% of the reaction products, while with a ratio of 1.6 the conversion of sulphide to sulphate was only 9.3%. In the continuous bioreactor, complete removal of sulphide was observed at sulphide volumetric loading rates as high as 1.6 mM/h (residence time of 10 h). Overall sulphide removal efficiency decreased continuously upon further increases in volumetric loading rate. However, the volumetric removal rate increased until a maximum value of 2.4 mM/h was obtained at a loading rate of 3.2 mM/h. The corresponding sulphide conversion and residence time were 76% and 5.6 h, respectively. As expected from the high ratio of sulphide to nitrate loading rates (1.7–1.9 mM/h), no sulphate was formed in the continuous reactor. Using the experimental data the value of maximum specific growth rate, saturation constant, decay coefficient, maintenance coefficient and yield were determined to be 0.36 h−1, 1.99 mM sulphide, 0.0014 h−1, 0.078 mmol sulphide/mg ATP h and 0.018 mg ATP/mmol sulphide, respectively.