Sustainable Autarky of Food-Energy-Water

Abstract

Meeting the demand for food, energy, and water to sustain the worldwide growth of urban population is a major challenge. Several recent reports have concluded that one approach to overcome this challenge is to recover and recycle resources within the food-energywater (FEW) nexus in urban settings. Urban wastewaters (UWW) are now being recognized as a resource, rich in nutrients and energy, rather than a waste stream that has to be treated and disposed of at the expense of significant energy input and associated environmental emissions. Reclaiming reusable water, nutrients, and energy from UWWs can contribute to autarky of FEW nexus and render the wastewater management process sustainable and potentially profitable. This paper presents a novel approach to treat UWW with the potential for high recovery of energy, nutrients, and water from UWW for use in food crop production. This approach entails cultivation of energy-rich algal biomass in primary-settled UWW followed by extraction of biocrude and nutrients from the algal biomass by hydrothermal liquefaction. A fraction of the recovered nutrients is recycled to boost biomass production while the rest can be stockpiled for use as fertilizer. Results from a pilot scale field study conducted at a local wastewater treatment plant confirmed that the algal system can achieve >80% removal of organic carbon, ammoniacal-nitrogen, and phosphates in UWW, meeting the respective discharge standards in a single step, with a batch process time of three days.