Waste to energy and circular economy: the case of anaerobic digestion

Anaerobic digestion (AD) can play a vital role in enhancing the circular economy of nutrients while producing renewable energy and providing an option for biowaste recycling. This makes AD interesting for energy, waste management, and agrifood sectors. The produced digestate retains the usable nutrients—nitrogen and phosphorus, while the degradation of organic materials by microbes produces biogas comprising carbon dioxide and methane. The resulting digestate can be utilized in the agricultural sector which links together waste valorization and food production, thus contributing to the closing of the loop of nutrients available in waste biomass, e.g., food waste. The produced biogas can be utilized directly in electricity and/or heat production or upgraded to biomethane to be distributed via the natural gas grid to be used in energy production or as vehicle fuel. To ensure that AD provides environmental gains the environmental performance must be evaluated, considering substrate, bioconversion process, and products.