With nearly 70% of the world population already concentrated in towns and cities, and with continuing trends in population growth and sprawl of metropolitan areas, provision of the basic human needs of food, energy, and water to the inhabitants is seen as a major challenge. Being net consumers of food, energy, and water, current urban infrastructure that continues to rely on obsolete technologies to provide these basic needs is not sustainable. Development of modern infrastructure that can recover and recycle energy and materials within the food-energy-water (FEW) sectors of urban sprawl is now recognized as one of the best options to improve the sustainability of both urban and agricultural systems.

In this paper, we report on algal-based, photosynthetically oxygenated waste-to-energy recovery (POWER®) system for recovering energy, water, and nutrients from urban wastewaters (UWW) that can be utilized in the food production sector. The POWER® system affords waste treatment, net energy production, and recovery of irrigation-quality water and high-purity crop fertilizers. The strain used in the POWER® system is Galdieria sulphuraria, capable of mixotrophic growth under elevated temperatures of 45 - 55^oC and low pH of 2 - 4. The POWER® system provides single-step removal of carbon and nutrients (nitrogen, N and phosphates, P) from UWWs through mixotrophic metabolism. The mixotrophic algal system is capable of incorporating all the C, N, and P in UWW into biomass without any energy input and without any loss of C as CO₂ as is the case in the current activated sludge systems. In addition, solar energy captured via photosynthesis is also incorporated into the biomass. The energy-rich biomass is then hydrothermally processed in the POWER® system to yield biocrude and biochar with solubilized N and P in concentrated form as byproducts for recovery and use as fertilizers. This paper includes details of development of the POWER® system and results from a pilot scale study conducted under field conditions at an urban wastewater treatment plant.