Hydrogen sulphide control in sewers by catalysing the reaction with oxygen

This work for the first time shows possible advantage of using ferrous as a catalyst to selectively oxidise hydrogen sulphide in sewer water where biological activity is present. Ferrous catalysed the oxidation reaction in all conditions, but the oxygen requirement for the chemical oxidation of sulphide varied depending on the initial conditions (pH, concentrations of sulphide and oxygen). For initial concentrations of O₂ and S^2- exceeding 2 mg/L, and a pH between 7.3 and 8.3, approximately 1 mg-O₂ was required to oxidise 1 mg-S^2-. For the typical conditions experienced in a sewer (pH < 8.0 and O₂ and S^2- < 2.0 mg/L), approximately 2.0 mg-O₂ is required to oxidise 1 mg-S^2-. The most efficient O₂ usage of 0.25-0.5 mg-O₂ was observed with initial O₂ and S^2- concentrations below 2.0 mg/L and a pH >8.1. The developed mathematical model described the experimental results over a wide range using only three coefficients. The catalytic effect of ferrous selectively increased the oxidation rate of S^2- in sewer water samples in which biochemical oxygen utilisation competes for oxygen. Further trials are needed to optimise the method for application in sewer systems where biofilm is present and varying conditions (temperature, H₂S concentration, oxygen consumption rate) exist.