Reverse Osmosis and Other Treatment Technologies - Global Drinking Water Management and Conservation - page 62

Fig. 4.11 Flow diagram of
the freeze desalination
process (Freeze Desalination
2014 )

feasibility of freeze desalination has been demonstrated, further research and
development remains before the technology is widely available (Carter 2013 ).

4.4 Relative Costs of Desalination Technologies

Among the choice of different technologies, RO is today ' is state-of-the-art technol-
ogy for high-quality water. RO is the most developed as well as the cheapest way to
convert brackish water or seawater into drinkable water, as we will now show.
The cost of a desalting plant is determined by a number of technical and eco-
nomic factors. The major cost categories are capital costs and operating and
maintenance costs. Capital costs are determined by the process type, plant capacity,
feed-water type and salinity, pretreatment required, product salinity desired, and
site-related costs for land, plant, and brine disposal. Operating and maintenance
costs include labor, energy, supplies, and general administrative expenses. The
economic characteristics of a desalting plant are usually expressed in two ways: the
capital cost per unit of installed capacity, such as dollars per gallon per day; and the
total annual product water costs, such as dollars per thousand gallons of annual
production. The product water costs are determined by the ratio of the total annual
costs to the annual water production. Since annual costs (including

xed costs) are
incurred at some minimum level even when no water is produced, the product water
cost is sensitive to the level of output and can increase signi cantly if the output

drops. High water costs often result from excessive “ down time ” for maintenance,

occasionally from shortages in suitable feed water, and from fluctuation in product

demand, all of which decrease annual output.
Dual-purpose plants can affect the economics of desalination. For example, in a
dual-purpose electric power/desalination plant, waste heat from electric power
production can be used for distilling seawater in the desalting plant, or steam
pressure from power production for desalination by RO.
Water costs of existing desalination plants vary widely, and frequently are not
completely comparable because of differences in the cost-determining factors