SUSTAINABLE DONNAN DIALYSIS PROCESS FOR SIMULTANEOUS RECOVERY OF NUTRIENTS FROM PIG MANURE AND TREATMENT OF BRACKISH GROUNDWATER FOR IRRIGATION

The Overall Aim of this research is to develop, test, and optimize a Donnan dialysis process for (i) recovery of phosphorus (as orthophosphate), nitrogen (as ammonium), and potassium from pig manure in lagoon systems and (ii) treatment of brackish groundwater to conditions suitable for irrigation. Donnan dialysis uses ion-exchange membranes to selectively separate ions, and our preliminary data confirms that these fundamentals can be extended to nutrient recovery from animal waste. Importantly, Donnan dialysis does not require electricity, specialized microbial consortia, or expensive chemicals. The main input to Donnan dialysis systems is salt. Here, we propose the use of brackish groundwater as the salt supply to not only offset operating costs, but also improve the water quality of brackish groundwater for subsequent use as irrigation water.The Goals of this project are to (1) obtain greater than 90% recovery of phosphorus and nitrogen from real pig manure using a Donnan dialysis reactor that requires no electricity, freshwater, or chemicals and (2) treat brackish groundwater to a total dissolved solids (TDS) content of less than 1400 mg/L (the acceptable limit for irrigation). We will investigate the following Specific Objectives:Objective 1: Generate novel hollow-fiber cation-exchange membranes (HF-CEMs) and hollow-fiber anion-exchange membranes (HF-AEMs) with high surface area-to-volume ratios that allow for rapid exchange reactions between salt ions in brackish groundwater and nutrients in pig manure;Objective 2: Conduct bench-scale Donnan dialysis experiments to identify selectivity and diffusion coefficients for orthophosphate (P(V); i.e., H2PO4-, HPO42-, and PO43-), magnesium (Mg2+), ammonium (NH4+), and potassium (K+) recovery from pig manure using brackish groundwater; and,Objective 3:Design, construct, and operate a pilot-scale Donnan dialysis reactor that can achieve 90% removal of NH4+ and P(V) from pig manure and treat brackish groundwater to irrigation water quality standards.The Significance of the proposed research stems from our innovative system to not only recover nutrients from real pig manure, but also treat brackish groundwater for irrigation purposes. Many ongoing efforts are investigating nutrient recovery from diverse waste streams, but most of those systems rely on traditional paradigms, such as precipitation of nutrient-laden solids after minor pretreatment or sorption of nutrients onto selective media. These approaches are prone to co-recovery of other contaminants and/or high operating costs that limit deployment in real settings. The low energy, chemical, and water requirements of the proposed Donnan dialysis process represent major advances for on-farm nutrient management, facilitating sustainable control of nutrient cycles, preventing water pollution, and generating slow-release fertilizers and alternative irrigation water sources for food production.