Sustainable Autarky of Food-Energy-Water (SAFE-Water)

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 input of considerable energy and associated environmental emissions. This paper presents an algal-based approach for treating UWWs to the mandated discharge levels in a single step and at the same time, recover net energy, nutrients, and water from UWWs for use in the food-energy-water sectors. The proposed approach entails cultivation of energy-rich algal biomass in primary-settled UWW, followed by hydrothermal liquefaction of the resulting algal biomass to recover its energy- and nutrient-contents. Results from a pilot scale field demonstration project are presented to demonstrate the feasibility of this approach. The pilot scale study conducted at a local wastewater treatment plant confirmed that the discharge standards for biochemical oxygen demand (BOD), nitrogen, and phosphorous could be met with a batch process time of 3 days. Recovery experiments showed that more than 20% of the ammoniacal nitrogen (N-NH3) and more than 90% of the phosphorous (P) in the primary-settled wastewater could be recovered as struvite by the proposed process.