Optimizing Food Waste Anaerobic Digestion: Substrate Composition, Total Solids, Bulking Agents and Digestate as a Source of Fertilizer

Food waste has rapidly emerged as a critical environmental challenge that is closely linked to both climate change and the depletion of natural resources. Anaerobic digestion (AD) offers a strategic approach to address this issue by simultaneously reducing organic waste and generating value in the form of renewable energy and nutrient-enriched digestate. This chapter examines how substrate characteristics, total solids (TS), and the addition of bulking agents (BAs) influence the performance and resilience of AD in food-waste management. The composition of carbohydrates, proteins, and lipids defines not only the potential biogas yield but also the operational limitations, while the carbon-to-nitrogen (C/N) ratio remains a crucial indicator for process balance. The TS content further determines microbial activity, methane productivity, and digestate quality, with semi-dry conditions (approximately 15–20% TS) often representing the optimal range. Moreover, bulking agents such as straw or sawdust enhance porosity, regulate moisture levels, and create favorable microbial habitats, thereby ensuring greater process stability and improved methane generation. By considering these interconnected factors, AD can be positioned not merely as a waste treatment method, but as a cornerstone of the circular economy—transforming food waste into clean energy and sustainable biofertilizer, while contributing to broader environmental and resource sustainability goals.