Finally, the operational cost of activated carbon was varied by varying three parameters, the production of H2S per animal-day, the adsorptive capacity of the carbon in g H2S/kg carbon, and the cost of carbon in CAN$/kg. The production of H2S on a per animal basis was calculated from H2S concentrations in the raw biogas of 250 ppmv and 3500 ppmv. If a small amount of air is injected into the headspace of the anaerobic digestion unit, the concentration of H2S can be reduced to approximately 250 ppmv through a microbial process [26], and, therefore, the activated carbon would be used as a final polishing of the gas. However, if the biogas is untreated, the concentration of H2S could reach 3500 ppmv, depending on the digester feedstock. The capacity of carbon was also varied, from 60 g H2S/kg carbon [17] to 500 g H2S/kg carbon
[4]. Finally, the cost of carbonwas varied from CAN$2/kg [8] to CAN
$12/kg, the price paid for a small amount of activated carbon for inlab
use.