Page - 64 - in Clean Water Using Solar and Wind - Outside the Power Grid

64 Clean Water Using Solar and Wind: Outside the Power Grid 5.1.4 Water treatment technologies The protection of human health is among the most important goals of water treatment systems. Any type of treatment must aim to reduce or inactivate potentially pathogenic organisms. Membrane separation is one methodology to remove harmful substances from the water. This aspect is emphasised in 5.2. Another technology to remove pathogens is by disinfection, as described in 5.4. Having saline or brackish water as the water source means that small molecules have to be removed in order to make the water drinkable or useable for irrigation. This is called desalination, and is discussed in 5.3. There are two main technologies to produce fresh water from seawater or brackish water: • Distillation, or thermal methods (heat treatment), and • Reverse osmosis (membrane process). Distillation is the oldest technology to obtain salt-free water. It uses a heat source to evaporate the water into steam and a cooling source to condense the steam into desalinated water. Regardless of the salt levels in the incoming water, the produced water will generally have a final salinity of less than 10 mg/l. The phenomena of osmosis and reverse osmosis (RO) have been known for about 100 years but only in the 1960s, with the development of synthetic membranes, did these principles become an industrial reality. The first membranes were made from cellulose acetate. Since then a large number of organic membranes, made of polymers, and even mineral membranes have been added to the list. An RO membrane only allows water to pass through and retains the solutes. Membrane desalination uses high pressure from electrically powered pumps to separate fresh water from seawater or brackish water using a membrane. In other words: the RO process is electric power driven. Membrane technology, mainly reverse osmosis (RO), is used for almost 60% of installed capacity. Membrane technologies continue to dominate the desalination market. For example, according to the International Desalination Association (www.idadesal.org), in 2017 membrane technology accounted for 2.2 million m3/day of annual contracted capacity while thermal processes accounted for just 0.1 million m3/day during the same period. Downloaded from https://iwaponline.com/ebooks/book-pdf/520710/wio9781780409443.pdf by IWA Publishing user