Journal of Energy Bioscience 2024, Vol.15, No.4, 221-232 http://bioscipublisher.com/index.php/jeb 223 purity syngas, making it a viable alternative to coal gasification (Sarkar and Praveen, 2017). Additionally, gasification of digestate from AD processes has been demonstrated to enhance energy recovery and produce valuable byproducts like biochar (Antoniou et al., 2019; Arora et al., 2021). 3.1.4 Pyrolysis Pyrolysis is the thermal decomposition of biomass in the absence of oxygen, producing bio-oil, syngas, and char. This process is highly versatile, allowing for the production of various energy carriers and valuable byproducts. Research has shown that optimizing pyrolysis conditions, such as temperature and heating rate, can significantly improve the yield and quality of pyrolytic products (Sarkar and Praveen, 2017; Mlonka-Mędrala et al., 2021). For example, pyrolysis of agricultural waste at higher temperatures increases the concentration of hydrogen and methane in the pyrolytic gas, making it a more efficient energy source (Mlonka-Mędrala et al., 2021). 3.2 Case studies of successful biomass energy projects Several successful biomass energy projects have demonstrated the feasibility and benefits of converting agricultural waste into energy. In Colombia, the combined use of direct combustion and anaerobic digestion has shown the potential to replace a significant portion of fossil fuel use, contributing to a more sustainable energy mix (Gutiérrez et al., 2020). Another notable project in Singapore's Gardens by the Bay utilized gasification to convert horticultural waste into biochar, which was then used as a soil conditioner and in concrete applications, showcasing a circular economy model (Arora et al., 2021). These case studies highlight the diverse applications and benefits of biomass energy projects in different contexts. 3.3 Economic feasibility and energy efficiency of biomass energy systems The economic feasibility and energy efficiency of biomass energy systems depend on several factors, including feedstock availability, technology choice, and system integration. Anaerobic digestion, for example, can be economically viable when coupled with gasification to enhance energy recovery and produce valuable byproducts (Antoniou et al., 2019). Direct combustion systems, while simpler, may require optimization to improve efficiency and reduce emissions (Sarkar and Praveen, 2017; Gutiérrez et al., 2020). Gasification and pyrolysis offer high energy efficiency and the potential for multiple revenue streams from syngas, bio-oil, and biochar, but they also require significant capital investment and technical expertise (Sarkar and Praveen, 2017; Arora et al., 2021; Mlonka-Mędrala et al., 2021) (Figure 1). Overall, the integration of multiple biomass conversion technologies and the adoption of circular economy principles can enhance the economic and environmental sustainability of biomass energy systems. Figure 1 Analysis of agricultural biomass pyrolysis process and its products (Adapted from Mlonka-Mędrala et al., 2021) 4 Conversion Processes for Organic Fertilizer Production 4.1 Composting techniques and methodologies 4.1.1 Windrow composting Windrow composting is a traditional method where organic waste is piled into long rows (windrows) and periodically turned to maintain aerobic conditions. This technique is widely used due to its simplicity and
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