Early distillation plants would use 15kWh/m3 for every ton of water processed. With power plants combined with the distillation plants, this number can be reduced to 8-12kWh/m3, but energy consumption is still relatively high. Using Reverse Osmosis (RO), this number can be reduced to 8kWh/m3. In order to reduce the costs of RO and to improve the lifespan of membranes, research is being directed towards improving the materials used for the semipermeable membranes. By adding an energy recycling system to RO systems, energy consumption can be reduced by 4-6kWh/m3.
The cost of RO is divided into a set up cost, energy consumption cost, and operational costs. The set up cost refers to how much it costs to build a plant. Most desalination plants are now financed by either Build-Operate-Transfer (BOT) or Build-Transfer-Operate (BTO). Unfortunately, it is rare to find the set up cost and the cost of supplies, which includes membranes, pre-treatment filtration systems, or the chemicals needed to add to any treated water, as this all depends on the quality of the water in a particular area.
Table 4-3 Estimate of Unit Water Producing Costs
|Set up||Energy cost||Supplies and operation||Total cost|
Although the costs for RO have reduced substantially, it is still relatively expensive and the quality of the water is inferior to that of tap water, with the Total Dissolved Solids being close to 400ppm. It is difficult to balance out costs and water quality, so, naturally, manufacturers and governments opt to choose the methods that are cheaper. Choosing to use RO over other methods may reduce costs, but the quality of water is still sacrificed.