Unveiling the impact of membrane wetting on ammonia recovery through membrane contactor technology

Membrane contactors as an emerging separation technology exhibit great potential for ammonia recovery due to the thermal and chemical stability. However, membrane wetting remains a significant challenge, hindering its broader industrial application. This study explores the effects of membrane wetting on the ammonia absorption rates through membrane contactor under varying operation conditions. The wetting depth was in-situ monitored by the ultrasonic technique. Results reveal that reducing the feed flow rate and lowering the absorbent concentration can effectively mitigate the decline in ammonia absorption rates, while increasing the feed pH does not affect the membrane wetting process but enhances the ammonia recovery. Furthermore, the rare-earth wastewater proves suitable for treatment via membrane contactor as it requires no additional low-surface-tension surfactant and has a higher ammonia concentration. Moreover, a developed model is conducted to elucidate the transport mechanism of ammonia through membrane contactor during wetting process. With the increased wetting depth during membrane contactor process, the boundary layer thickness gradually increased, significantly strengthening the transfer resistance. This study provides an insight into further understanding the ammonia mass transfer through membrane contactor under wetting conditions.