## 5 Results and Discussions  
### BMP for the GCC Region  
Table 4 shows a comparison between the biomethane prediction per gram of COD loading and wastewater dry sludge. The results indicated that estimation of BMP using COD loading yielded 144 mL/g of COD, which is nearly 30% more than the volume of BMP estimated using the elemental composition of dry wastewater sludge. Variations in estimations can be attributed to the factors discussed in Section 4.3, such as cell synthesis, biodegradability, C/N ratio, and the model's simplifying assumption that all carbon content in COD is converted to CH\({}_{4}\) and CO\({}_{2}\). While the model estimations are based on stoichiometric ratios of input/output, it does not estimate the CO\({}_{2}\) volume when COD is used since it does not distinguish between the partitioning CO\({}_{2}\) in the aqueous and gas phase (biogas). Consequently, additional inputs such as temperature, pH, and composition were employed to estimate the total biogas volume (CH\({}_{4}\) and CO\({}_{2}\)) (Table 4). The empirical formula for dry sludge yielded a mean biogas volume of 139.5 mL/g, consisting of 72% biomethane and 28% CO\({}_{2}\) (Table 4). A literature review of the experimental BMP of wastewater sludge revealed that CH\({}_{4}\) yields vary greatly, from 50 mL/g to >1000 mL/g of sludge. These variations can be attributed to the type of sludge (primary, activated, or mixed), operating conditions (temperature and pH), organic loading rates, pre-treatment of sludge, and reactor of experimental setup [16; 22; 26; 27; 29; 50; 51; 52; 53; 54; 55; 56]. Table 5 presents the BMP of wastewater sludge produced in the GCC region. These estimates are based on the values in Table 4 and on the assumption that the chemical composition for sludge produced in GCC states is similar to that produced in Kuwait. Thus, the BMP estimated from the chemical composition was 30% less than the BMP estimated from COD loading. The biomethane potential of sludge for the entire region ranged between 232-334 \(\times\) 10\({}^{6}\) m\({}^{3}\) of biomethane (Table 5), with a total heat value up to 10.7 trillion BTUs annually. The lower end was BMP estimated from the chemical composition and the upper end was BMP estimated using COD loading. Saudi Arabia, the largest and most populated member state in the GCC, accounted for nearly 71% of all biomethane production, followed by the UAE at 15%. The remaining four counties accounted for 14% of all BMP. In its raw form, biogas can be utilized directly as a cooking fuel, fed to CHP plants, or can be upgraded to biomethane, to be injected into the gas grid for consumption by power plants. Biomethane production in the GCC region can generate up to 1665 GWh of electrical energy annually (Table 6), an amount equivalent to the current electricity generation from combined wind and solar energy sources. Regarding individual GCC member states, the UAE could gain a 13-19% increase in renewable energy (electricity) production when utilizing biomethane, while KSA could gain up to 537% increased electricity production from renewable sources. Desalinated seawater could be generated from renewable energy sources if coupled with RO technologies. Hypothetically, if all biomethane is used to power RO desalination units, the potential production of low-carbon-footprint freshwater can be as high as 302 \(\times\) 10\({}^{6}\) m\({}^{3}\) annually (6% of all current desalinated water production) (Table 6). As the GCC states aim to increase the share of renewable sources (wind and solar) within the electricity sector, additional power flexibility is required to offset fluctuating