Scaling and fouling in membrane distillation for desalination applications: A review

• Review: temperature, flow rate, SI, feed type, specific salt effects in MD fouling
• Module type, and temperature and concentration polarization greatly affect fouling.
• High temperature prevents MD biofouling.
• Particulate fouling can be easily avoided by microfiltration.
• Reducing feed pH, membrane superhydrophobicity, and antiscalants prevent MD scaling.

Membrane distillation (MD) has become an area of rapidly increasing research and development since the 1990s, providing a potentially cost effective thermally-driven desalination technology when paired with waste heat, solar thermal or geothermal heat sources. One principal challenge for MD is scaling and fouling contamination of the membrane, which has gained growing attention in the literature recently as well. The present paper surveys the published literature on MD membrane fouling. The goal of this work is to synthesize the key fouling conditions, fouling types, harmful effects, and mitigation techniques to provide a basis for future technology development. The investigation includes physical, thermal and flow conditions that affect fouling, types of fouling, mechanisms of fouling, fouling differences by sources of water, system design, effects of operating parameters, prevention, cleaning, membrane damage, and future trends. Finally, numerical modeling of the heat and mass transfer processes has been used to calculate the saturation index at the MD membrane interface and is used to better understand and explain some of trends reported in literature.