Higher solubility at alkaline conditions is very significant for an efficient treatment process of gaseous H2S(,) by reducing the gas-liquid transfer limitations. Nevertheless, the alkaline biodegradation process of H2S can be limited when sulfide concentrations are inhibitory. At alkaline conditions (pH > 9), the abiotic chemical sulfide oxidation can attain relatively high rates. A series of abiotic and biotic kinetic experiments of oxygen consumption were performed at pH 10. For the biological oxidation, an alkaliphilic sulfide oxidizing consortium (ASBC) isolated from a soda lake was used. The intermediates from the chemical sulfide oxidation in alkaline and aerobic conditions did not inhibit the activity of ASBC at six-fold concentration of that where H2S inhibition was detected (1.19 mM). Stoichiometries and kinetic expressions for the chemical sulfide oxidation to pentasulfide (S-5(2-)) and its further oxidation to thiosulfate (S2O32-) are proposed and validated with experimental data. The faster oxic chemical sulfide oxidation under alkaline conditions could be advantageous for the biological oxidation to sulfate by reducing the concentration of the inhibiting sulfide. These results suggest that the chemical and the biological oxidation processes can be segregated, allowing higher sulfide loading rates. (c) 2006 Elsevier Inc. All rights reserved.