sustainability Review A Conceptual Framework for Incorporation of Composting in Closed-Loop Urban Controlled Environment Agriculture Ajwal Dsouza 1,* , Gordon W. Price 2, Mike Dixon 1 and Thomas Graham 1,* 1 Controlled Environment Systems Research Facility, School of Environmental Sciences, University of Guelph, 50 Stone Road East, Guelph, ON N1G 2W1, Canada;
[email protected] 2 Department of Engineering, Faculty of Agriculture, Dalhousie University, PO Box 550, Truro, NS B2N 5E3, Canada;
[email protected] * Correspondence:
[email protected] (A.D.);
[email protected] (T.G.) Abstract: Controlled environment agriculture (CEA), specifically advanced greenhouses, plant factories, and vertical farms, has a significant role to play in the urban agri-food landscape through provision of fresh and nutritious food for urban populations. With the push towards improving sustainability of these systems, a circular or closed-loop approach for managing resources is desirable. These crop production systems generate biowaste in the form of crop and growing substrate residues, the disposal of which not only impacts the immediate environment, but also represents a loss of valuable resources. Closing the resource loop through composting of crop residues and urban biowaste is presented. Composting allows for the recovery of carbon dioxide and plant nutrients that can be reused as inputs for crop production, while also providing a mechanism for managing and valorizing biowastes. A conceptual framework for integrating carbon dioxide and nutrient recovery through composting in a CEA system is described along with potential environmental benefits over conventional inputs. Challenges involved in the recovery and reuse of each component, as well Citation: Dsouza, A.; Price, G.W.; as possible solutions, are discussed.