Journal of Energy Bioscience 2024, Vol.15, No.2, 118-131 http://bioscipublisher.com/index.php/jeb 126 study that showed a 1.2-fold increase in biomethane production and higher annual revenue compared to traditional waste treatment methods (Salman et al., 2017). The economic benefits of AD extend beyond energy production, as the use of digestate as a biofertilizer can reduce the need for synthetic fertilizers, leading to cost savings for farmers (Stoknes et al., 2016; Muscolo et al., 2017). 8 Case Studies and Practical Applications 8.1 Successful case studies of anaerobic digestion plants using agricultural waste Several successful case studies highlight the effectiveness of anaerobic digestion (AD) plants in converting agricultural waste into biomethane. For instance, the integration of pyrolysis and anaerobic digestion processes has shown promising results. By coupling the anaerobic digestion of biodegradable waste with the pyrolysis of lignocellulosic or green waste, a significant increase in biomethane production was achieved. The biochar produced from pyrolysis was used as an adsorbent in the digester, enhancing the biomethane content and supporting a stable microbial community. This integrated process demonstrated an approximately 1.2-fold increase in biomethane volume and an overall efficiency of 67%, compared to 52% for a stand-alone anaerobic digestion system (Salman et al., 2017). Another notable case is the anaerobic co-digestion of agricultural wastes and waste-activated sludge, which has been shown to produce bioenergy and biochemicals, contributing to a circular bioeconomy. This process has been optimized by adjusting feedstock compositions and operating conditions, resulting in enhanced biomethane production (Pan et al., 2021). 8.2 Lessons learned from pilot and commercial-scale projects Pilot and commercial-scale projects have provided valuable insights into the practical applications of anaerobic digestion technology. For example, the anaerobic digestion of orange peel in a semi-continuous pilot plant demonstrated the potential for biomethane production from citrus waste. The study found that under mesophilic conditions, the highest daily specific methane yield was achieved at an organic loading rate (OLR) of 1.0 gTVS L-1 d-1 and an essential oil supply rate (EOsr) of 47.6 mg L-1 d-1. However, partial inhibition occurred at higher OLR and EOsr values, highlighting the importance of optimizing these parameters for successful operation (Zema et al., 2018). Additionally, the use of hydrothermal carbonization (HTC) coupled with anaerobic digestion for the treatment of municipal solid waste has shown significant improvements in biomethane production. The HTC process increased methane production by up to 363% compared to untreated waste, demonstrating the effectiveness of this combined approach (Lucian et al., 2020). 8.3 Regional and global perspectives on the adoption of anaerobic digestion technology The adoption of anaerobic digestion technology varies regionally and globally, influenced by factors such as regulatory support, economic incentives, and technological advancements. In Europe, for instance, the upgrading of biogas to biomethane and its injection into the gas grid has been explored as a means to connect decentralized biomass production to a centralized gas grid. This approach has been economically viable even without subsidies, promoting anaerobic digestion as a key driver for a new bio-industry (Verbeeck et al., 2018). Globally, the interest in enhancing anaerobic digestion efficiency through the application of biochar has been growing. Biochar has been shown to enhance hydrolysis, acidogenesis-acetogenesis, and methanogenesis, as well as alleviate inhibitor stress, thereby promoting stable and efficient biomethane production (Pan et al., 2019). In summary, the successful implementation of anaerobic digestion technology in various case studies and pilot projects, along with regional and global perspectives, underscores its potential in converting agricultural waste into valuable biomethane. The lessons learned from these projects provide a roadmap for optimizing and scaling up anaerobic digestion processes to achieve sustainable and efficient waste management solutions.
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