Improving the sustainability of organic waste management practices in the food-energy-water nexus: A comparative review of anaerobic digestion and composting

With global population growth, the security of food, energy and water is becoming more challenging. Both anaerobic digestion (AD) and composting are waste management methods that are plausible approaches to address this challenge by reusing organic waste and generating value-added products. In this paper, recent research on AD and composting is summarized, and differences in the technical, economic, and environmental aspects of AD and composting, and their potential to improve the sustainability of waste management, are examined. Recent research on AD has focused on process enhancement and valorization of end products, while composting research has emphasized ways to shorten composting period and reduce odor and greenhouse gas (GHG) emissions. Strategies to enhance AD and composting processes are similar, but the operational parameters that affect microbial activity, including inoculation, aeration, temperature, moisture, C/N ratio, and pH, can differ. AD can be economically more advantageous than composting, depending on plant scale and valorization of end products, while composting is more profitable at smaller scales (e.g. < 20,000 t). Therefore, AD may be favored for centralized treatment, such as for food waste or sewage sludge; whereas, composting may be preferred for decentralized treatment, such as for on-farm animal manure. Environmentally, AD is favorable in terms of lower GHG emissions due to production of biogas as a renewable energy source. In composting, no single aeration scheme or additive has been found to be effective in reducing odor and GHG emissions simultaneously. Further research on AD and composting should be conducted to improve precision control and optimization, process design, product value, pollution control, and economic and environmental analyses, and more information needs to be provided to decision makers.