Ammonia recovery and fouling mitigation of hydrolyzed human urine treated by nanofiltration and reverse osmosis

Abstract

Ammonia is a critical compound due to the numerous industry products which rely on its production such as fertilizer, refrigerant gas, and textile manufacturing. Ammonia is also a pollutant in wastewater due mainly to the source of human urine. Urine diversion allows for treatment and recovery of the ammonia in urine. Reverse osmosis (RO) and nanofiltration (NF) are widely used and trusted water and wastewater treatment processes. Through novel selective separation, the ammonia in the urine can be recovered to produce an ammonia product with economic value. However, cross-flow RO and NF on real human urine for selective ammonia recovery has been untested. Therefore, this project investigated the use of RO and NF to recover ammonia from hydrolyzed human urine in a cross-flow system where both ammonia permeation and fouling experiments were performed. For both RO and NF, complete ammonia permeation (0% rejection) was observed while still achieving high rejection of total organic carbon (>92%) and salts (SO₄²⁻ and PO₄³⁻ were >97% and Cl⁻, Na⁺, and K⁺ ranged from 91–97% for RO and 83–94% for NF). Notably, there was no statistical difference in rejection of NH₃, TN, TOC, SO₄²⁻, PO₄³⁻, Na⁺, and K⁺ between RO and NF. Microfiltration pretreatment greatly reduced the extent of fouling on the membrane surface and was deemed necessary for long-term operation. An economic analysis showed that RO and NF systems had the lowest process cost, $4.69–4.72 per m³, and highest product offset, $0.4 per kg, when compared with other ammonia recovery processes.