Review of liquid-liquid hollow fiber membrane contactor for ammonia recovery from wastewater: Membrane, feed and receiving solution

Massive and accumulated emissions of ammonium nitrogen are crucial pollutants, and ammonium nitrogen in wastewater is valuable resources to the production of fertilizer. Liquid-liquid hollow fiber membrane contactor (LL-HFMC) has been proven to apply in ammonia recovery with high separation efficiency, low cost and saving energy consumption. This review focused on three components of LL-HFMC, including membranes, feed and receiving solution, summarized the principles of LL-HFMC, effects and developments of hydrophobic hollow fiber membranes. Besides traditional hydrophobic hollow fiber membranes fabricated by PP, PVDF and PTFE three types of polymers, some novel membrane materials and modifications are utilized through casting, electrospinning and other methods, aiming at enhanced mechanical properties, chemical durability or hydrophobicity. The characteristic properties and compositions of feed and receiving solution were analyzed. In order to improve ammonia recovery efficiency and meet the requirements of near-zero discharge, it may become inevitable to realize ammonia recovery process by using liquid-liquid hollow fiber membrane contactor at low ammonium ion concentration, and it is necessary to optimize the process, prepare novel hydrophobic hollow fiber membranes with high ammonia selectivity, low water flux and good acid/alkaline resistance. The summary and comprehensive analysis in this review provides guiding fundaments and outlooks for researches and applications in the future.