When biodegradation occurred, H2S co-degraded with organic matter and was converted to carbon dioxide (CO2), water and sulfate [7]. As shown in Fig. 5, CO2 concentration increased progressively from the bottom stage to the top stage of the biofilter due to CO2 production and accumulation at each stage of the filter. It can also be observed that durring the 30-day operation of the filter CO2 production increased and peaked at CO2 inlet concentration of 50 ppmv when the botton stage of the filter could not achieve complete removal of H2S. Further drop in outlet CO2 concentration especially at the bottom stage also coincide with drop in removal efficiency of the bottom stage of the filter indicating that the production of CO2 was inhibited at higher H2S inlet concentrations.