Demonstration of Power Generation from Fertilizer Solutions via Pressure-Retarded Osmosis

Abstract

HighlightsMechanical work can be generated from fertilizer via pressure-retarded osmosis.Laboratory tests show up to 5 Wh of energy recovered per kg of fertilizer.Tradeoffs between energy recovery and power generation are demonstrated.Maintaining power above 5 W m-2 is reasonable given current membrane technology.Abstract. Large amounts of energy are released when concentrated fertilizers are diluted in water. In this study, we demonstrate the use of fertilizer to generate useful mechanical work via pressure-retarded osmosis (PRO). A number of common single solutes and fertilizer blends were analyzed using both experimental and numerical methods. Laboratory test trials showed energy recovery of up to 5 Wh kg-1 of fertilizer and power of up 6 W m-2 of membrane area given commercial cellulose triacetate membranes. A drop in power was demonstrated throughout the fertilizer PRO batch process, and the resulting tradeoffs between energy recovery and power density are discussed. Simulation results suggest that high-performance membranes can be used to maintain elevated power above 5 W m-2 throughout the batch process, while recovering approximately 5 Wh kg-1. The loss of valuable fertilizer via leakage to the feed stream was found to be less than 1% of the initial fertilizer mass, suggesting that this non-ideal dynamic can be reasonably minimized. Implications at the food-energy-water nexus are discussed. Keywords: Fertilizer osmosis, Forward osmosis, Fertilizer energy, Food-energy-water nexus.