Contactless membrane distillation for effective ammonia recovery from waste sludge: A new configuration and mass transfer mechanism

Abstract

Membrane distillation (MD) is an attractive technology to remove and recover ammonia (NH3) from waste sludge; however, it suffers from membrane fouling problems. In this study, a contactless MD system was developed by introducing an air gap between the hydrophobic membrane and feed solution to largely eliminate the fouling problems. Results show that the overall NH3 transfer coefficient by contactless MD was (1.49 ± 0.05) × 10−5 m/s, more than 7 times greater than that of conventional MD. In continuous operation with a short retention time of 20 min, a high NH3 recovery (>80%) from fermented sludge liquor and a clean membrane without foulant attachment were maintained, while the conventional MD system failed in 12 h due to severe membrane fouling. After NH3 recovery, the sludge liquor was turned into a preferable organic carbon source for utilization. This innovative contactless MD can recover ammonia from various waste liquids.