9 Seawater Desalination Plants: Heavy Coastal Industry
97
1. The overall energy consumption is lower, about one half to one third depending on
the technology. Lower energy consumption means less atmospheric emissions.
2. The conversion ratio is higher, about 30 to 35%. This means that the concentration of
the brine is higher and attains about 130% of the intake water. At the same time the
amount of outlet water is lower than that of a thermal desalination plant.
3. RO plants do not require less chemicals per amount of intake water, but since the
conversion rate is higher the emission load compared to produced freshwater is lower.
A marked difference is the addition of sulfuric acid to the feed water: 30 mg 1-1 means
about 100 t 1000000 m- 3 freshwater product.
4. The temperature increase is negligible. There are no thermal outfall problems.
5. A true comparison regarding chemical emissions is difficult since data on chemical
use are incomplete.
6. Technological problems are less well solved than for thermal plants. This is the main
reason for the present predominance of thermal plants.
7. RO plants produce much more solid waste than thermal plants. There are no acceptable solutions for the disposal or re-use of the membrane systems.
Simply stated, thermal plants are favourites of countries rich in fossil energy. RO
plants are more common in developed countries. In the Red Sea/Gulf region the number
of thermal desalination plants is about 280, the number of RO plants about 112. The
ratio of the capacities is 6800000 to 425000 m 3 freshwater per day, respectively
(Wangnick, pers. comm.).
9.8
The Targets: Coastal Sub-Ecosystems
The Gulf coasts of the Arabian countries do not vary greatly in geomorphologic structures (Purser and Seibold 1973). Nevertheless, there is a rich diversity of biotopes, some
of international nature protection interest (Basson et al. 1981; Sheppard et al. 1992).
Sensitive marine Gulf-specific biotopes are, e.g. shallow bays, coral reefs, seaweed meadows, intertidal sand- and mudflats. Sensitive coastal biotopes are mangrove areas,
saltmarshes, rocky shores, bird islands, coastal sabkhas, cyanobacterial mats, sand
beaches and beachrock flats. The sensitivity of these biotopes to thermal desalination
plants is different. To regard the sensitivities properly, a sensitivity index is proposed
(see below). According to the variety of biotopes there is also a rich diversity of species
(Jones 1986; Price et al. 1993). These properties require site-specific examinations in
environmental impact studies.
The use of natural marine resources belongs in a biological context. The Gulf is a
productive sea and a rich source of fish and shrimps (Sheppard et al. 1992). Even if
fishery is negligible within the gross domestic product, it is present all along the Gulf
coast and supplies the food market with goods of high quality and variety. Productive
fishery is a good indicator of a healthy marine ecosystem. The number of people engaged in traditional and modern fishery should not be underestimated. Conflicts between the interests of desalination industry and fishery can be expected wherever
desalination plants are erected or enlarged.
An impressive and illustrated introduction to the general habitat varieties of the
western Gulf has been given by Basson et al. (1981). Jones et al. (no year) demonstrate
97
1. The overall energy consumption is lower, about one half to one third depending on
the technology. Lower energy consumption means less atmospheric emissions.
2. The conversion ratio is higher, about 30 to 35%. This means that the concentration of
the brine is higher and attains about 130% of the intake water. At the same time the
amount of outlet water is lower than that of a thermal desalination plant.
3. RO plants do not require less chemicals per amount of intake water, but since the
conversion rate is higher the emission load compared to produced freshwater is lower.
A marked difference is the addition of sulfuric acid to the feed water: 30 mg 1-1 means
about 100 t 1000000 m- 3 freshwater product.
4. The temperature increase is negligible. There are no thermal outfall problems.
5. A true comparison regarding chemical emissions is difficult since data on chemical
use are incomplete.
6. Technological problems are less well solved than for thermal plants. This is the main
reason for the present predominance of thermal plants.
7. RO plants produce much more solid waste than thermal plants. There are no acceptable solutions for the disposal or re-use of the membrane systems.
Simply stated, thermal plants are favourites of countries rich in fossil energy. RO
plants are more common in developed countries. In the Red Sea/Gulf region the number
of thermal desalination plants is about 280, the number of RO plants about 112. The
ratio of the capacities is 6800000 to 425000 m 3 freshwater per day, respectively
(Wangnick, pers. comm.).
9.8
The Targets: Coastal Sub-Ecosystems
The Gulf coasts of the Arabian countries do not vary greatly in geomorphologic structures (Purser and Seibold 1973). Nevertheless, there is a rich diversity of biotopes, some
of international nature protection interest (Basson et al. 1981; Sheppard et al. 1992).
Sensitive marine Gulf-specific biotopes are, e.g. shallow bays, coral reefs, seaweed meadows, intertidal sand- and mudflats. Sensitive coastal biotopes are mangrove areas,
saltmarshes, rocky shores, bird islands, coastal sabkhas, cyanobacterial mats, sand
beaches and beachrock flats. The sensitivity of these biotopes to thermal desalination
plants is different. To regard the sensitivities properly, a sensitivity index is proposed
(see below). According to the variety of biotopes there is also a rich diversity of species
(Jones 1986; Price et al. 1993). These properties require site-specific examinations in
environmental impact studies.
The use of natural marine resources belongs in a biological context. The Gulf is a
productive sea and a rich source of fish and shrimps (Sheppard et al. 1992). Even if
fishery is negligible within the gross domestic product, it is present all along the Gulf
coast and supplies the food market with goods of high quality and variety. Productive
fishery is a good indicator of a healthy marine ecosystem. The number of people engaged in traditional and modern fishery should not be underestimated. Conflicts between the interests of desalination industry and fishery can be expected wherever
desalination plants are erected or enlarged.
An impressive and illustrated introduction to the general habitat varieties of the
western Gulf has been given by Basson et al. (1981). Jones et al. (no year) demonstrate