Sustainable Waste-to-Energy Technologies: Anaerobic Digestion

Abstract

Anaerobic digestion is a widely accepted technology employed worldwide to convert the massive amounts of food waste produced every day, into methane—a gas that can be subsequently used for heat and electricity generation in combined heat and power systems. Food wastes originate from a variety of sources—from retail and commercial outlets, to food processors, farms, and food service enterprises. The robustness of anaerobic digestion, however, allows processing multiple food waste streams of different physicochemical characteristics and at varying organic loading rates in a single reactor. In a well-designed and operated anaerobic digester, the production of methane should be fairly stable over time. The performance and stability of the process depends on several key parameters, including organic loading rate and hydraulic retention time, nutrients, volatile fatty acids, alkalinity, long-chain fatty acids, ammonia, and pH, all of which are discussed in this chapter. A thorough monitoring and process control system can prevent process upsets and system failure, while a healthy and robust digester microbiota will speedup digester recovery if process stability is disrupted. Anaerobic codigestion of food-waste streams, primarily with agricultural manures, is likely to be the leading trend of future systems, as it allows increased organic loading rates and improved process stability relative to stand-alone food waste anaerobic digestion systems. The generation of renewable energy from AD-based biogas, to offset fossil fuel-based electricity and prevent the release of harmful greenhouse gases, including methane, will help to increase energy independence and to meet the CO2 emission reduction goals most countries have subscribed under the Paris agreement. As countries continue to put more emphasis on sustainable waste management practices, and begin to see food waste and other organic substrates as resources, opportunities will continue to emerge. Economic systems worldwide are gradually shifting to a circular economy approach, providing more incentives and benefits for waste-to-energy systems, and resulting in revenue opportunities that are beginning to outweigh the initial capital costs for nontraditional energy generation systems such as anaerobic digestion.