Recovery of ammonium nitrogen from human urine by an open-loop hollow fiber membrane contactor

Abstract

Recovering nitrogen from separately collected urine can potentially reduce cost and energy consumption of wastewater nitrogen removal and fertilizer production. In this study, we developed an open-loop hollow fiber membrane contactor (HFMC) to recover ammonium nitrogen from hydrolyzed human urine. Ammonia capture performance at various feed velocities and pH values was investigated. Be different from closed-loop HFMCs, the feed flow velocity is a vital operating parameter. The ammonia capture efficiency decreased from 80.13% to 33.06% when the feed flow velocity increased from 2.61 × 10−5 to 46.83 × 10−5 m s−1. Increasing feed pH from 10.0 to 12.0 enhanced ammonia capture efficiency from 62.12% to 80.13% by promoting the feed solution free ammonia fraction to increase the driving force. Ammonia mass transfer was investigated based on resistance-in-series model. Shell side mass transfer dominated the ammonia capture in the open-loop HFMC. The empirical shell side Sherwood correlation, Sh=17.4Dh1-φLRe0.6Sc0.33, fitted the experimental data well. The used polypropylene membrane showed good ion rejection performance with more than 99.44% rejection efficiency of PO43− and K+ which can be further recovered. The membrane also showed good stability during the ammonia capture experiments. The hydrophobicity, mechanical and pore properties did not significantly change.