Nutrient Recovery from Urine using Selective Ion Exchange

Urine source-separation and treatment has the potential to radically transform wastewater management whereby water, nutrients, and energy are recovered. Despite the potential of urine source-separation and treatment, it has not been widely implemented because of an absence of engineering strategies that are efficient in resource recovery and practical to implement. Accordingly, the goal of this research, which is part of a larger project examining technical and social challenges of urine source-separation and treatment, is to identify ion exchange processes that achieve maximum and selective recovery of nutrients from urine. The specific objectives are to (1) quantify phosphate uptake by ion exchange as a function of urine chemistry and dilution conditions and (2) evaluate whether pharmaceuticals can be selectively removed by ion exchange in the presence of phosphate.Synthetic urine is being used in all experiments. Both fresh and hydrolyzed urine are prepared by adding appropriate chemicals, i.e., ammonia, urea, chloride, phosphate, sulfate, carbonate, sodium, potassium, calcium, and magnesium, to deionized water. A polymeric ligand exchange (PLE) resin that contains iron(III) oxide particles is being used for Objective 1 based on previous work that demonstrated high phosphate selectivity in the presence of competing anions. Several strong base anion exchange resins are being used for Objective 2. Preliminary kinetic tests demonstrated that phosphate ion-exchange equilibrium is achieved in 2 h. Equilibrium tests are being used to systematically evaluate the effects of pH, ionic strength, competing species, and dilution conditions on phosphate recovery, which are designed to simulate urine dilution with tap water, greywater, and secondary treated wastewater. Objective 2 is investigating diclofenac removal by ion exchange under different urine chemistry conditions.Results for phosphate uptake by the PLE resin are shown below (Figure 1). The resin showed high selectivity for phosphate with 98% and 87% phosphate removal from fresh urine and hydrolyzed urine, respectively. The different initial concentration of phosphate in fresh urine and hydrolyzed urine is due to spontaneous mineral precipitation during urea hydrolysis. Although large amounts of PLE are required to remove phosphate, urine represents less than 1% of the volume of domestic wastewater so a small reactor would be needed to treat source-separated urine. The ion exchange isotherm shows that PLE has a similar selectivity for phosphate under different urine chemistry. This presentation will highlight the major conclusions of this research and discuss the application of selective ion exchange for recovery of nitrogen, potassium, sulfur, and metals from urine and wastewater.