Hybrid membrane distillation: Resource, nutrient and energy recovery

Membrane distillation (MD) is a promising alternative thermal-based membrane process that can achieve high-quality freshwater across various impaired water sources. However, the performance of MD as a stand-alone system remains a challenge for attaining commercialization. Hybrid MD - the integration of MD with other processes, offers a practical approach for performance enhancement as well as the possibility to achieve valuable resource recovery. This review details the performance and related challenges of various hybrid MD systems with a focus on resource recovery. On the basis of recovering valuable salt/element from impaired water sources, hybrid MD-crystallizer is limited to the recovery of major salts. Comparatively, MD-adsorbent exhibits potential for selectively recovering valuable elements, which may offset treatment cost. Meanwhile, hybrid MD-bioreactor (MDBR) and MD-forward osmosis (MD-FO) are especially favorable combinations for attaining water reclamation from the wastewater industry and recovering nutrients and biogas that mitigates environmental pollution. Simultaneous recovery of water and energy can be attained with hybrid MD-pressure retarded osmosis (MD-PRO) and MD-reverse electrodialysis (MD-RED). Overall, this review highlights the favorable potential of hybrid MD for recovering resources in niche applications. Future suggestions for improving hybrid MD are discussed, specifically pilot-scale application, module configuration and membrane development.