Journal of Energy Bioscience 2024, Vol.15, No.2, 118-131 http://bioscipublisher.com/index.php/jeb 123 4.3 Biological pre-treatments Biological pre-treatments involve the use of enzymes or microbial consortia to break down complex organic materials. Enzyme addition can significantly enhance the hydrolysis of lignocellulosic materials, leading to higher biomethane yields (Rawoof et al., 2020). The use of microbial consortia can also improve the efficiency of anaerobic digestion by synergizing the effects on microbial communities, balancing nutrients, and reducing inhibitory effects (Neri et al., 2023). Co-digestion, which involves the simultaneous digestion of multiple types of organic waste, has been shown to enhance biogas production by 25%-400% compared to mono-digestion (Rawoof et al., 2020). 4.4 Impact of pre-treatment methods on the efficiency of anaerobic digestion The impact of pre-treatment methods on the efficiency of anaerobic digestion is substantial. Physical, chemical, and biological pre-treatments can significantly enhance the breakdown of complex organic materials, making them more accessible to anaerobic microbes and thus increasing biogas yields. For example, thermal pre-treatment at lower temperatures can accelerate the kinetics of the anaerobic digestion process, leading to higher biomethane production (Salman et al., 2017). Chemical pre-treatments like acid and alkaline treatments can improve the hydrolysis of lignocellulosic materials, resulting in higher methane yields (Almomani and Bhosale, 2020). Biological pre-treatments, including enzyme addition and co-digestion, can synergize microbial activity and improve nutrient balance, further enhancing biogas production (Rawoof et al., 2020; Neri et al., 2023). In summary, the integration of various pre-treatment methods can significantly improve the efficiency of converting agricultural waste into biomethane using anaerobic digestion technology. Each method has its advantages and can be selected based on the specific characteristics of the feedstock and the desired outcomes. 5 Optimization Strategies for Anaerobic Digestion 5.1 Co-digestion of agricultural waste with other organic materials Co-digestion involves the simultaneous digestion of multiple organic substrates, which can enhance the efficiency and stability of the anaerobic digestion process. Studies have shown that co-digestion of agricultural waste with other organic materials, such as food waste, floatable oil, and bioplastics, can significantly improve biomethane production. For instance, co-digestion of food waste and floatable oil resulted in higher biomethane yields and better system stability compared to mono-digestion (Meng et al., 2015). Additionally, co-digestion of bioplastics with biowastes has been found to efficiently degrade bioplastics and improve biogas production (Abraham et al., 2020). The synergistic effects of co-digestion help balance nutrient content, reduce inhibitory effects, and enhance microbial community interactions, leading to increased biomethane yields (Rawoof et al., 2020; Pan et al., 2021). 5.2 Optimization of process parameters (temperature, pH, HRT, OLR) Optimizing process parameters such as temperature, pH, hydraulic retention time (HRT), and organic loading rate (OLR) is crucial for maximizing biomethane production. The optimal temperature range for anaerobic digestion is typically mesophilic (30℃-40℃) or thermophilic (40℃-50℃), with higher methane yields observed in the thermophilic range (Noor et al., 2021). Maintaining an optimal pH range of 6.8-7.2 is essential for stable methane production (Rawoof et al., 2020). Adjusting HRT and OLR can also significantly impact the efficiency of the digestion process. For example, reducing the retention time from 72 to 20 hours improved hydrogen yield, while an optimal C/N ratio of 16-27 enhanced methane productivity (Rawoof et al., 2020). Proper control of these parameters ensures a stable and efficient anaerobic digestion process (Rawoof et al., 2020; Noor et al., 2021; Pan et al., 2021). 5.3 Use of additives and supplements (trace elements, biochar, etc.) The addition of various additives and supplements can enhance the anaerobic digestion process. Trace elements such as iron, nickel, and cobalt are known to improve microbial activity and methane production. Biochar, a byproduct of pyrolysis, has been shown to increase biomethane content and support the development of a stable microbial community when added to the digester (Salman et al., 2017). Other additives, such as enzymes and micronutrients, can also enhance the breakdown of complex organic materials and improve overall process
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