Final Report: Sustainable Wastewater Treatment: Nutrient Upcycling of Ammonia into FertilizerEPA Grant Number: SU835513
Title: Sustainable Wastewater Treatment: Nutrient Upcycling of Ammonia into Fertilizer
Investigators: Barak, Phillip , Anderson, Tyler , Bashar, Rania , Calkins, Cody , Herrman, Grant , Voellinger, Logan
Institution: University of Wisconsin - Madison
EPA Project Officer: Levinson, Barbara
Project Period: August 15, 2013 through August 14, 2014
Project Amount: $14,996
RFA: P3 Awards: A National Student Design Competition for Sustainability Focusing on People, Prosperity and the Planet (2013) RFA Text | Recipients Lists
Research Category: Pollution Prevention/Sustainable Development , P3 Challenge Area - Water , P3 Awards , Sustainability
The US sends 1.87 million metric tons of nitrogen from its homes and 0.47 million metric tons from its industries to centralized wastewater treatment plants annually and much of this nitrogen is volatilized as N2 and the greenhouse gas N2O in order to meet current water quality standards. Despite this, fossil fuels are expended to fix billions of dollars’ worth of nitrogen from the atmosphere. Recently, electrodialysis has been explored as a promising device to recover nitrogen from swine manure. Electrodialysis is a separations technology in which ions are removed from one stream and concentrated in another in response to an electrical field, and has traditionally been used in the desalinization industry to deionize brackish water. While the energy costs of the electrodialysis have been unable to compete with other techniques that produce a commodity as cheap as water, nitrogen is a far more valuable commodity, with anhydrous ammonia currently at $400 per (short) ton. We propose to build an ammonia recovery process to be incorporated into existing wastewater treatment facilities to remove and concentrate the ammonium from the wastewater stream and recover a high value commercial fertilizer, ammonia.
Attempts at ammonium concentration and recovery as ammonia in the literature have been limited by a non-selective approach of ion concentration, scale formation in ion exchange membranes, and product streams with pH too low for optimal ammonia recovery. We have designed and built a novel nine-cell lab scale electrodialysis cell equipped with selective membranes in order to address these issues. Initial work has shown that our electrodialysis cell can concentrate ammonia by 30% over its original concentration in a single pass.
Our P3 team has made an initial calculation of costs of electrodialyzed ammonium compared to chemically synthesized ammonia. Using our 9-cell electrodialysis stack and a 2000 ppm N solution (as ammonium bicarbonate), 20 volts was required to drive one amp of current through the stack. Using the governing equations relating electrical current to ionic flow through use of the Faraday constant (26.8 A·h/mol), we calculated that 3200 kWh would be required to separate and concentrate 1 ton of ammonia at 100% current efficiency. This would break even at an energy cost of $0.126 per kWh.
The Dane County Manure Digester, Waunakee, WI, a public/private consortium, operated by Clear Horizons, LLC, a subsidiary of Pieper Power, Inc. generates about 2 MW by burning biogas derived from manure of three surrounding dairy farms and commercial food waste from the surrounding area. With a projected 100,000 gallons per day at a concentration of 1800 ppm ammonium (NH4+)-N, it is estimated that the Dane County Manure Digester could produce 250 tons per year of ammonia (NH3-) fertilizer.
Ammonia is the most concentrated of the various nitrogen fertilizers, at 83% N by weight, with urea at 46% and ammonium nitrate at 35%, and various liquid N fertilizers at 28 to 33% N. Industrial ammonia synthesis by the Haber-Bosch process is usually located near reliable sources of natural gas, which means in the U.S., near the Gulf Coast. Ammonia pipelines carry product to the Midwest but many areas that might otherwise use ammonia are underserved. Electrodialysis of ammonia could provide a locally-sourced high analysis fertilizer that can displace lower-analysis N fertilizers from other regions, reducing transport and storage costs.