Kinetics of hydrogen sulfide oxidation in sanitary sewer systems

There is a need to evaluate different technologies such as FeCl 2, H2O2 and O2 addition as odor and corrosion control alternatives to determine required dosages and detention times. The goal of this research is to study the kinetics of H2S removal using the techniques commonly employed in sanitary sewer systems to determine the effectiveness of each process. To achieve this objective a laboratory simulation of these chemicals additions was carried out using completely mixed BOD bottles as batch-reactors. The BOD reactor was filled with a 7 mg/L H 2S solution. FeCl2, 50%-H2O2, O 2 and a combination of FeCl2 and H2O2 were added to the reactors containing H2S solution and the concentration of H2S remaining was measured after certain reaction times. A rate expression based on experimental data was generated using the integration method. The rate constants (k) and the order of the reaction (n) were calculated from the concentration-time data. For a range of temperature of 12°C and 14°C and pH 7, the oxidation of H2S with FeCl2 adheres to second-order reaction kinetics. The removal of H2S using H2O2 is well described by the third-order kinetic for a temperature range between 10°C and 17°C and pH 7. H2S oxidation by the combination of FeCl2 and H2O2 can be described by third-order reaction kinetic in a temperature range of 15-20°C and pH 7. The removal of H2S injecting O2 to force mains suggests a second-order reaction kinetic at 22.5°C and pH 7. Summing up, FeCl2 treatment requires the addition of large quantities to be effective. Also, O2 injection was ineffective across the range of pure oxygen investigated. Conversely, 50% H2O2 is the most effective chemical control strategy for the mitigation of H2S investigated. Maximum percent H 2S removals using combination of FeCl2 and H2O 2 were in the 90s. In this case most of the H2S is oxidized by H2O2, which means that FeCl2 addition does not have a significant effect on the removal of H2O2 . In every case, the initial concentration of the reactant used has a significant effect on the values of both k and t1/2 .