Elucidating the inherent fouling tolerance of membrane contactors for ammonia recovery from wastewater

Recovery of ammonia from wastewater has garnered interest due to its resource potential as fertilizers, refrigerants, and hydrogen carriers. Membrane contactors (MCs) are an effective process for ammonia recovery from wastewater streams, but the impact of membrane fouling on the process has seldom been explored. Here, we examine the dependency of membrane fouling on MC process conditions and elucidate the inherent process tolerance to fouling. A hydrophobic PVDF membrane was employed between ammonia-rich, anaerobicallydigested food wastewater (feed) and a sulfuric acid stream (draw). With >95% ammonia recovery, minimal membrane fouling was observed despite the high organic loading in feed. By performing MCs in isothermal and non-isothermal modes, we identified the deterministic role of transmembrane water vapor flows on membrane fouling. Subsequently, deliberately fouled membranes were employed in the isothermal MC, where >70% ammonia recovery from the wastewater was still observed. This markedly high recovery from the fouled membranes was further examined using partially covered membranes with impermeable films that mimic fouled membranes. The intricate porous structure in the membrane allows for facile ammonia transfer, limiting the impact of severe membrane fouling. Our study shows the great potential of isothermal MCs for reliable and sustainable ammonia recovery from diverse wastewaters.