Because salt and other small components are the most common compounds in wastewater from the process industry, desalination techniques are likely to be suitable as treatment processes in many cases. Although membrane distillation (MD) is a well-known technology for desalination and water treatment, it is not yet applied in industry. Membrane distillation differs from other membrane technologies in that the driving force for desalination is the difference in vapor pressure of water across the membrane, rather than total pressure. The membranes for MD are microporous and hydrophobic, which allows water vapor (but not liquid water) to pass. The vapor pressure gradient is created by heating the source water, thereby elevating its vapor pressure. The major energy requirement of MD is low-grade thermal energy. It is expected that the total costs for water purification with membrane distillation will be lower than $0.50/m3, even as low as $0.26/m3, depending on the source of the thermal energy required for the evaporation of water across the membrane. Because low-grade heat is readily available in industry, MD can very well be applied for desalination of process streams.
- water costs
- Air gap membrane distillation