Techno-economic analysis of desalination technologies

With 30% of the countries of the world facing high level of water stress, the problem of fresh water scarcity needs to be tackled. Since saline water represents 97.4% ofthe water of the Earth, desalination is one of the main resources that can be used to mitigate the water shortage. In this review, the four main technologies belonging to the different separation processes (membrane, thermal and hybrid processes) in desalination are analysed through the scientific desalination literature and throught he data collected of more than 1,300 real desalination plants. Reverse Osmosis (RO-membrane process) is the most dominant technology with a capacity share of the 70%. This technology consists in the separation of salts by forcing saline water to pass through a hydrophilic polymeric membrane, applying external pressure to overcome the osmotic pressure. The Specific Energy Consumption (SEC) of this method is low (2-6 kWh/m3) and only needs electric power to function. RO plants can output a variable amount fresh water (from <100 m3/day to >500,000 m3/day) at low competitive prices (0.14-2.46 $/m3). Although prone to fouling and scaling and the inability to treat highly contaminated water, RO is found to be the most suitable desalination technology reviewed. On the other end, Membrane Distillation (MD-hybrid thermal-membrane process) is still in an early development stage, with low average capacities (<100 m3/day), high SEC (>100 kWh/m3) and high water costs (0.61-4.90 $/m3). It consists in the evaporation of the feed water, that is then filtered by forcing the vapour through a hydrophobic polymeric membrane and is found to be the least suitable technology. In the middle range, Multi-Effect Distillation (MED) and Multi-Stage Flash (MSF) are purely thermal processes with high average capacities (from <100 m3/day to >800,000 m3/day) and medium SEC (5-28 kWh/m3 of combined electric and thermal energy). The water costs are very similar between the two (0.52-2.30 $/m3 for MED and 0.52-2.50 $/m3 for MSF), which make them competitors of RO. The separation of salts from water is done by the evaporation of the feed water in an array of stages inside the desalination unit. All the technologies can be powered through renewable energies, which is one of the main research branches in desalination.