Eco-effectiveness, eco-efficiency, and the metabolism of a city: A multi-sectoral analysis

The vision of Cities as forces for good within the environment is explored herein by proposing a multisectoral analysis that accounts for nutrients, water, energy. The main purpose is to identify those elements in the urban system that can offer more opportunities of improvement with regard to eco-efficiency and eco-effectiveness indicators, and how different sectors, i.e. water, food, forestry, energy, and waste management, interact between each other. For this, (i) a computational model is designed using concepts of Substance Flow Analysis (SFA) together with mass and energy balances, and (ii) a set of indicators are defined to assess the improvement or worsening of the system. (iii) Both model and indicators are simulated under the Regionalized Sensitivity Analysis (RSA) framework to account of uncertainty and test the relevance of prospective technological innovations, i.e. structural changes. The paper presents a case study based on the Upper Chattahoochee Watershed in the south-eastern United States, in which the nitrogen (N) cycle is investigated under two scenarios: 0% and 100% urine source separation implementation. Results reveal that animal feed and fossil fuels are the major flows of N in the system. Urine separation showed to be critical for some aspects of the system as described by the behavior of the set of indicators.