This study was conducted to assess the economic feasibility of electricity generation from biogas in small
pig farms with and without the H2S removal prior to biogas utilisation. The 2% potassium iodide (KI)
impregnated activated carbon selected as H2S adsorbent was introduced to a biogas-to-electricity generation
system in a small pig farm in Thailand as a case study. With the average inlet H2S concentration of
about 2400 ppm to the adsorption unit, the H2S removal efficiency could reach 100% with the adsorption
capacity of 0.062 kg of H2S/kg of adsorbent. Under the reference scenario (i.e., 45% subsidy on digester
installation and fixed electricity price at 0.06 Euro/kWh) and based on an assumption that the biogas
was fully utilised for electricity generation in the system, the payback period for the system without
H2S removal was about 4 years. With H2S removal, the payback period was within the economic life of
digester but almost twice that of the case without H2S removal. The impact of electricity price could
be clearly seen for the case of treated biogas. At the electricity price fixed at 0.07 Euro/kWh, the payback
period for the case of treated biogas was reduced to about 5.5 years, with a trend to decrease at higher
electricity prices. For both treated and untreated biogas, the governmental subsidy was the important
factor determining the economics of the biogas-to-electricity systems. Without subsidy, the payback period
increased to almost 7 years and about 11 years for the case of untreated and treated biogas, respectively,
at the reference electricity price. Although the H2S removal added high operation cost to the
system, it is still highly recommended not only for preventing engine corrosion but also for the environment
benefit in which air pollution by H2S/SO2 emission and impact on human health could be potentially
reduced.