Sustainable Management of Digestate from the Organic Fraction of Municipal Solid Waste and Food Waste Under the Concepts of Back to Earth Alternatives and Circular Economy

The anaerobic digestion (AD) of the organic fraction of municipal solid waste (OFMSW) and food waste achieves both environmental and economic benefits. This bio-process, well-known for producing biogas, is used extensively for industrial applications all over the world. Despite the use of AD across the world, the overall sustainability of this process as a source of an alternate fuel (i.e., biomethane) is intrinsically linked to the successful management of one of its major byproducts, the digestate. In order for the digestate to be classified as a “product” rather than a “waste” and to achieve regulatory compliance, this liquid stream needs to undergo biological or physicochemical treatments. The most common treatment for digestate is the use as a soil amendment. Nutrients surplus, variable agricultural seasonal requirements, escalating transportation cost, and market acceptance (e.g., risk for food safety) represents the major obstacle for the use of digestate for agricultural applications. Therefore, it is necessary to study alternative approaches for digestate management and utilization options. One alternative concept is the Back to Earth Alternative (BEA) whose aim is to bring appropriately treated residues back to their non-mobile state, as they were extracted from the earth to be used as raw materials, which would achieve actual closing of the materials cycles. Similarly, the same concept can be introduced into the digestate management process, with the goal of reducing resource costs and mitigate potential impacts on climate change, by employing a more holistic circular economy model instead of linear economy model commonly referred to as “take-make-dispose”. The overarching aim of this study is to introduce the BEA and circular economy concepts into the digestate management process taking into consideration the initial quality of the digestate and the techniques and processes necessary to meet the specific regulatory and quality requirements for the utilization of this waste stream for different applications. Cost benefit analysis and environmental impact were also evaluated for each BEA.