Recovering Nitrogen as a Solid without Chemical Dosing: Bio-Electroconcentration for Recovery of Nutrients from Urine

Abstract

This letter presents the proof of concept of a novel bio-electroconcentration system (BEC), a hybrid microbial electrolysis/electrodialysis cell specifically designed to recover nitrogen (as ammonia NH4-N), phosphorus (as phosphate PO4-P), and potassium (as K+) from urine. Using a synthetic urine medium, the BECs could reach high current densities of up to 37.6 A m–2 at Ewe values of 0.0 versus the standard hydrogen electrode (SHE) and 50 A m–2 at 0.2 V versus SHE, which in turn drove the removal and recovery of N, P, and K at rates of 7.18 kg of NH4-N m–3 day–1, 0.52 kg of PO4-P m–3 day–1, and 1.62 kg of K+ m–3 day–1 into a concentrate stream (containing 1.87 M NH4-N, 0.29 M PO4-P, and 0.18 M K+). Finally, this communication demonstrates the recovery of a nitrogen-rich solid from the synthetic urine (in the form of pure NH4HCO3 crystals with 17% N content) without any chemical additions via the flash-cooling of the produced nutrient-rich concentrate to 4 °C. These two new products may help facilitate the reuse of urine nutrients in the fertilizer or protein production industries of the future.