Chapter 7 - Non-traditional water resources: Desalination and treated wastewater

Abstract

Since early 1950s, Kuwait embarked on desalination as the most practical solution to its water supply problems and has used it successfully ever since. The capacity of desalination plants in the Arabian Gulf countries and the world is very high and the growth of world quantity of desalinated water shows changes in the proportion of the total contributed by commercially available processes, distillation and membrane processes, multistage flash distillation (MSF), reverse osmosis (RO), and multi-effect distillation (MED). The most important distillation methods are multistage flash distillation and multi-effect distillation. Both involve the evaporation of saline feed water and its condensation into fresh water by leaving dissolved substances in the waste brine. In multistage flash, a stream of brine flows through. The pressure in each chamber is maintained at a lower level than the saturation vapor pressure of the water, where a part of it flashes into steam and is then condensed. In multi-effect distillation, evaporation takes place as a thin film of feed water moves over a heat transfer surface, which is usually the outside of horizontal tubes. The vapor formed in each effect is condensed in the next by providing a heat source for further evaporation. Energy saving is made if the vapor from the last effect is re-compressed thermally or mechanically. In multi-effect distillation method, fewer stages are involved than in multistage flash distillation method.