Novel Processes to Recover Nutrients from Human Urine and Poultry Litter and Ensure Resource Sustainability in Urban Systems

Nutrients, such as nitrogen and phosphorus, are essential agricultural inputs needed to produce food for urban populations. Novel strategies are required to sustainably harvest these resources. One option is to recover nitrogen and phosphorus from nutrient-rich waste streams, such as human urine and poultry litter. Nutrient recovery will not only constitute new, and potentially lucrative, markets, but also reduce environmental impacts from major point (wastewater treatment plants) and non-point (agriculture) sources. Although human urine constitutes less than 1% of municipal wastewater, 50% of the nitrogen and 75% of the phosphorus in wastewater come from urine. Concentrated poultry operations in the Delmarva Peninsula (USA) annually generate about 1,000,000 tons of phosphorus-rich poultry litter, approximately 180 tons per square mile. With new regulations limiting nutrient discharge from wastewater treatment plants and nutrient runoff from agricultural fields, new, sustainable technologies are needed. In this project, we explored two innovative approaches to recover nutrients from urine (liquid waste) and poultry litter (solid waste). To recover nutrients from urine, we pursued the following specific objectives: (1.1) demonstrate nutrient recovery by Donnan dialysis, which uses ion-exchange membranes to selectively concentrate nutrients in a draw solution composed of simple salts; (1.2) examine the effects of membrane type, draw solution composition, and competing ions on nutrient transport across the ion-exchange membrane; and, (1.3) develop a continuous-flow Donnan dialysis reactor. Bench- scale experiments recovered 51% of the ammonium, 66% of the potassium, and 67% of the phosphorus in synthetic urine. Nutrient recovery was dependent on ion diffusion through the membrane. Diffusion rates were determined for two draw ions, namely chloride (4.5 × 10#$$ m2 min-1) and formate (8.6 × 10#$$ m2 min-1), to identify opportunities to offset inorganic/organic salt content in waste solutions. While the high chloride concentration in urine exerted some competitive effects, high phosphorus recovery was still achieved. The continuous-flow reactor employed tubular ion-exchange membranes to achieve 61%, 93%, and 67% recovery of phosphorus, magnesium, and potassium in a synthetic waste solution. The following objectives guided nutrient recovery from poultry litter: (2.1) investigate pH- dependent extraction of nutrients from poultry litter; (2.2) optimize conditions for precipitation of value-added fertilizers from filtered poultry litter extracts; and, (2.3) develop an automated nutrient recovery system to process poultry litter and generate struvite-based fertilizers. At pH 4- 5, the extraction efficiencies for phosphorus and nitrogen were greater than 80% and 85%, respectively. The composition of the precipitated nutrient-laden solids was controlled by solution pH, aeration, and addition of chelating agents. These measures resulted in preferential formation of struvite (NH4MgPO4·6H2O) or potassium-struvite (KMgPO4·6H2O). An automated lab-based pilot reactor was developed and used to assess the overall mass balance on nutrients and determine product purity. The aforementioned technologies require minimal chemical and energy inputs to transform waste streams into value-added fertilizers. In this manner, we can reduce nutrient pollution into the environment, decrease the energy/mining costs associated with current fertilizer production, and improve food security. These strategies can be applied to other liquid and solid waste streams to ensure sustainable urban systems.