## 5 Results and Discussions
### BMP for Kuwait and the Potential Emission Reduction  
The estimated biogas composition for this study was 72% biomethane and 28% CO\({}_{2}\) by volume (Table 4). Annual dry sludge production in Kuwait is approximately 158,000 tonnes, which yields a BMP of 14.7 \(\times\) 10\({}^{6}\) m\({}^{3}\), with a total heat content of 471.7 billion BTUs. Biomethane could displace 13 \(\times\) 10\({}^{6}\) m\({}^{3}\) of natural gas, or approximately 86,000 barrels of crude oil or other liquid fuels annually (Table 7). The decision on which fuel to displace depends on economic and environmental factors which capture the scarcity, energy security, and environmental facets of such fuels. Kuwait exports crude oil and, consequently, displacing crude oil would increase export capacity for the country, while displacing HFO would yield in maximum emissions reductions. The findings of this case study are meant to demonstrate the fuel savings and emission reductions of utilizing biogas as a clean and renewable fuel. While data on sewage and wastewater sludge were not available for the other GCC states at the time of this study, such potential benefits can be extrapolated to other GCC states since they all have similar fossil fuel powered plants.  
Two emissions scenarios were compared for this case study (Table 8). The base scenario was where electricity is produced from estimated fossil fuels and the dry sludge is stored or disposed of in a landfill. The alternative scenario was where sludge is anaerobically converted to biogas and utilized as an energy source to produce electricity. It is worth noting that emissions from sludge disposal were based on the assumption that dry sludge undergoes anaerobic decomposition in a landfill, with similar performance to an anaerobic digestor. Regarding the base scenario, the combustion of fossil fuels emits CO\({}_{2}\), NOx, and CH\({}_{4}\). Additionally, dry sludge emits CH\({}_{4}\) and CO\({}_{2}\) under anaerobic conditions. In this scenario, the combustion of natural gas emission emits roughly 25 \(\times\) 10\({}^{6}\) Kg of CO\({}_{2}\) annually, while the other liquid fuels emit 35-38 \(\times\) 10\({}^{6}\) Kg of CO\({}_{2}\) annually. Sludge disposal emissions in this scenario were 9.6 \(\times\) 10\({}^{6}\) Kg and 13 \(\times\) 10\({}^{6}\) of CH\({}_{4}\) and CO\({}_{2}\), respectively. The total GHG emissions in this scenario ranged from 280,000-293,000 tonnes of CO\({}_{2}\) equivalents. In the alternative scenario, dry sludge underwent AD in a reactor where CH\({}_{4}\) is captured and used to as a substitute to fossil fuels. The combustion of biomethane emits CO\({}_{2}\) and NOx. Note that no carbon capture was assumed in either scenarios, rather CO\({}_{2}\) was assumed to be released into the atmosphere. All emissions were converted into CO\({}_{2}\) equivalents and reported as GHG emissions (Table 8). The employment of biomethane as a clean, renewable fuel and the displacement of fossil fuels could potentially reduce GHG emission by 86% when compared to the base scenario (Table 8). The substantial reduction in GHG emissions is due to biomethane capture, which has 25\(\times\) fold increased global warming potential than CO\({}_{2}\), that would otherwise be released from landfills into the atmosphere.  
\begin{table}
\begin{tabular}{c c c} \hline \hline  & **Value** & **Unit** \\ \hline Biomethane & 14,729 & 10\({}^{3}\) m\({}^{3}\) \\ Heat content & 471,770 & mmBTU \\ Fuels volumes with equivalent energy content & \\ Natural Gas & 12,965 & 10\({}^{3}\) m\({}^{3}\) \\ Crude oil & 86,619 & bbl \\ Gas Oil & 87,885 & bbl \\ HFO & 84,838 & bbl \\ \hline \hline \end{tabular}
\end{table}
Table 7: BMP for Kuwait and the volumes fossil fuel displacements annually.