Oxidation of biologically produced elemental sulfur under neutrophilic conditions

BACKGROUND: Previous research on a biotrickling filter for the removal of high loads of H2S showed that accumulation of elemental sulfur (S0) when dealing with high H2S concentrations could lead to reactor clogging. Since S0 can also serve as substrate for sulfur-oxidising bacteria, this study investigates the biological oxidation of S0 as a remediation strategy. RESULTS: Results indicated that biological oxidation of S0 inside a clogged biotrickling filter occurred at a comparable rate to those reported for stirred tank reactors. When biologically produced dried and powdered S0 was manually added as a substrate in stirred tank reactor experiments, significantly lower S0 oxidation rates were found compared to those for biological S0 freshly produced in situ. It was speculated that either the powdered S0 particle size or the surface properties hindered S0 bioavailability even in a well-stirred environment. Respirometric experiments with the same powdered S0 and acetone-dissolved S0 confirmed that biological oxidation of S0 was basically limited by the solid S0 bioavailability. CONCLUSIONS: Therefore, results showed that S0 oxidation basically depends on S0 bioavailability and that Sulfate volumetric production rates as high as 3.48 mmol SO42- h-1 L-1 can be achieved inside a clogged biotrickling filter probably due to the high biomass retention capacity. Overall, the results indicate that biological oxidation of S0 can be considered a suitable strategy for unclogging bioreactors clogged with S0.Peer Reviewe