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Abstract

The first-order kinetics of hydrogen sulphide oxidation was examined in two trickling biofilter reactors using residence time distribution analysis and the Tanks in Series model for packed bed reactors. The reactor's liquid phase was maintained at pH 5.0 in Reactor 1 and pH 2.5 in Reactor 2. Carbon dioxide was added as a supplemental carbon source in varying concentrations. Hydrogen sulphide concentrations to 300 ppm were investigated. The Tanks in Series parameter N was found to be approximately 7 for both reactors, and was insensitive to the air flow rate. The hydrogen sulphide removal rate constant decreased with increasing hydrogen sulphide inlet concentration. Substrate inhibition was suspected due to the toxic nature of hydrogen sulphide on the trickling biofilter microbes, but was shown to be insignificant at the hydrogen sulphide concentrations under investigation. At equal hydrogen sulphide inlet concentrations, the oxidation rate constant at pH 5.0 was approximately twice that at pH 2.5. The greatest removal rate constant found was k=0.130 s⁻¹ at a hydrogen sulphide inlet concentration of 50 ppm. The Tanks in Series model was shown to be a viable means of estimating the 1st-order rate constant for the removal of gaseous hydrogen sulphide from air streams in a trickling biofilter. A scale-up approach using the Tanks in Series model to determine the kinetic rate constant and literature data for determining the parameter N in a production-scale trickling biofilter is briefly discussed. This will aid in the application of economical and environmentally preferable trickling biofilters to the emissions control systems for Kraft pulp mills and other H₂S producing industries.