Minimization of resource consumption and carbon footprint of a circular organic waste valorization system

Abstract

The efficient management of municipal organic waste (OW) will contribute to the transition to a circular economy of nutrients. The goal of this work is to determine the optimal configuration of a waste management system that valorizes the OW generated in Cantabria. The model was developed with the EASETECH and the DNDC softwares, and it assumes that the products generated from the OW (compost, digestate, struvite, and ammonium sulfate) are applied to land to grow corn. The closed-loop perspective of the system is given by the application of these products, which results in a reduction in the consumption of the industrial fertilizers required for the production of food, a fraction of which becomes OW in a later life cycle stage. A superstructure comprising technologies to manage OW was developed. A mixed integer linear programming problem was formulated for the multiobjective optimization of the flows of OW that are sent to each technology according to these objective functions to be minimized: the carbon footprint of the system (CF), the landfill area occupied by OW (LFA), and the consumption of nonrenewable raw materials (NR-RM). It was found that a combination of different technologies is required to attain a trade-off between the objective functions. The minimization of the CF leads to a system configuration with a high N circularity and the maximal values of LFA and NR-RM, whereas the minimal consumption of NR-RM is achieved at the scenarios with low N recovery rates. This indicates that an enhanced circularity of resources does not necessarily entail that the overall consumption of natural resources and the emission of environmental burdens of the system decrease.