Urban water and food security in this century and beyond: Resource-smart cities and residents
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PERSPECTIVE
Urban water and food security in this century and beyond: Resource-smart cities and residents Jan-Olof Drangert
Received: 7 December 2019 / Revised: 12 May 2020 / Accepted: 18 July 2020
Abstract The urban world population will increase from 3 to 8.5 thousand million in the 21st century. Cities become hot spots of both demand for water and global food and for disposed used water and nutrients. Sustainability requires that resource flows through our cities are co-managed and connected to agriculture. Reduced use of harmful chemicals in consumer products facilitates treatment to a quality that allows reuse/recycling of water and nutrients. A solid and liquid waste hierarchy can assist in ordering measures. A novel flexible water balance can guide city infrastructure and keep toilet water separate. New watersaving equipment can substantially reduce water use without losing personal comfort. The combination of these new approaches ascertains access to safe urban water, and that recovered nutrients from cities can substitute half of chemical fertilisers needed in food production. Now, thousands of new cities and suburbs provide unique opportunities to develop resource-smart and sustainable flows. Keywords Recycled plant nutrients Recycled urban water Solid and liquid waste hierarchy Sustainable access to water and food Urban water balance Water-efficient urban infrastructure
INTRODUCTION Sustainability requires that we accept the fact that Mother Earth and the embracing atmosphere are limited—despite being immense (Folke et al. 1997). For the first time in human history, the Earth’s system boundary is being crossed (Rockstro¨m et al. 2009; Steffen et al. 2015; Zhang et al. 2015). Today, emissions of greenhouse gases, cropland use, and application of nitrogen and phosphorus have
exceeded Natures capacity to provide physical resources and sinks in a sustainable way (Springmann et al. 2018). This realisation has helped spark a deepened interest in sustainable management of existing resources. We urgently need to address and consider the whole value chain from exploiting natural resources via production and consumption, to management of so called waste. In this article the focus is on potentials and limits to enhance urban management of water and nutrients for perceived needs. The last century and a half saw a wasteful use of water and removal of urban organic matter. Sewers were introduced to move excreta and wastewater away from urban areas in order to solve urban sanitary challenges (Melosi 2000). No one opposed measures to reduce human exposure to pathogens, but the loss of the fertilising value in urban waste was initially of great concern (e.g. Hugo 1862). Moreover, there has been a tendency to overestimate Nature’s capacity to accommodate rising volumes of nutrient-rich but contaminated wastewater and sludge in seemingly endless water bodies. The world now witness the consequences with, e.g. eutrophic lakes and dead bottoms of seas (UNEP 2006). We have also overstated the atmosphere’s capac
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