Journal of Energy Bioscience 2024, Vol.15, No.5, 289-300 http://bioscipublisher.com/index.php/jeb 292 contributing to a more sustainable and circular economy (Nanda et al., 2023). Figure 2 Schematic diagram of biodiesel production from bio-wastes through the synthesis of free fatty acids and triacylglycerol (TAG) in oleaginous microorganisms (Adopted from Zhang et al., 2020) Image caption: Acetyl-CoA: acetyl-coenzyme A; Gly3P: glycerol-3-phosphate; PEP: phosphoenolpyruvate; LPA: Lysophosphatidate; PA: phosphatidate; DAG: diacylglycerol; ACC: acetyl-CoA carboxylase; MAT: malony-CoA:ACP transacetylase; FAS: fatty acid synthetase; FAT: acyl-ACP-thioesterase. Adapted from Spagnuolo et al. (2019) and Liang and Jiang (2013) with permission/license granted by the publisher (Adopted from Zhang et al., 2020) 4 Pre-treatment of Kitchen Waste 4.1 Physical and chemical pre-treatment methods Pre-treatment of kitchen waste is a crucial step to enhance its biodegradability and efficiency in biohydrogen production. Various physical and chemical methods have been explored to break down complex organic matter into simpler compounds that are more accessible to microbial degradation. Physical methods include thermal treatments such as freeze-thaw cycles and pressure-depressure techniques, which have shown to significantly improve solubilization and biogas production (Ma et al., 2011). Chemical methods, on the other hand, involve the use of acids, alkalis, or other chemical agents to alter the chemical structure of the waste. For instance, alkali pre-treatment at high pH levels has been effective in increasing hydrogen yields from food waste and sewage sludge mixtures (Nam, 2023). Additionally, mild thermal pre-treatment has been found to enhance the solubilization of carbohydrates and reduce the lignocellulosic matrix, thereby improving anaerobic biodegradability (Pagliaccia et al., 2019). 4.2 Optimization of pre-treatment for efficient microbial degradation Optimizing pre-treatment conditions is essential to maximize the efficiency of microbial degradation and biohydrogen production. Studies have shown that the choice of pre-treatment method and its parameters, such as temperature, pH, and duration, can significantly influence the yield of biohydrogen. For example, thermal shock
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