Real Risk

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ATER IS A

very scarce commodity in the West Asia

region, known as one of the most arid areas in the

world. Severe water-related problems have been

compounded in recent years by a sharp increase in water demand,

due mainly to the fast-growing population and rapid socio-

economic development. In order to reduce the gap between

supply and demand, countries of the Economic and Social

Commission for Western Asia (ESCWA) region were compelled

to develop large-scale, non-conventional schemes.

Experience in the Gulf states indicates that desalination tech-

nology has developed to a level where it can serve as a very reliable

source of water at a price comparable to that of other conven-

tional and non-conventional water sources. Desalination was

proved to be the most feasible alternative to meet future water

requirements and considered as a strategic option for satisfying

current and future domestic water supply requirements. Evidently,

desalination has become a major dependable source of water for

large urban centres in most Gulf countries. This is particularly

true when required water quality standards, social acceptability,

and political vulnerability are all taken into consideration.

On a global level, the Gulf region produces over half of the

world’s desalinated water. Unfortunately, the environmental risks

associated with the construction and operation of desalination

facilities have not been given adequate consideration by the insti-

tutions concerned. There follows a brief inventory of those risks.

Environmental risks at the plant’s intake

There are two types of intake effects associated with power-

desalination: impingement effects and entrainment effects. As

the seawater going into the power-desalination plant is screened

and filtered, aquatic organisms are removed from it. This is called

the impingement effect. Entrainment effects take place when

smaller organisms passing through filters find their way through

the process where they get exposed to chemicals, higher temper-

ature or pressure – conditions which are severe, or which

endanger their existence. Both of these effects pose the risk of

increased mortality rates for plankton of all types as well as small

fish. This in turn may result in reduced population and hence

reduced biodiversity, production and yield.

Experience from the Gulf region indicates that cooling seawa-

ter for power-desalination has resulted in the impingement of

large numbers of fish and macro-invertebrates. Several cases of

massive fish kills were also reported in the vicinity of power-

desalination plants.

Environmental risks of brine water discharge

In principle, desalination plants separate saline water into two

streams: a low dissolved solid concentration stream (fresh water

or desalinated water), and another stream containing the remain-

ing dissolved solids (brine reject or blow-down). To extract,

separate and concentrate the salts in the reject brine solution,

intensive thermal or electrical energy is required. The character-

istics of the reject brine are a direct function of the quality of the

feed water, the desalination technology used, the per cent recov-

ery, the chemical additives used within the process, the

construction materials and the proficiency of the operators.

Most of the large-scale desalination plants in the ESCWA

Region are located on the coastlines of the Gulf and Red Sea.

Obviously, they discharge their brine concentrate into the adja-

cent near-shores. It is believed that rapid mixing and dilution are

the keys to reducing risks associated with disposal of brine in the

sea. The risk magnitude of brine discharge depends to a large

extent on the physical, chemical and biological characteristics of

the receiving near-shore marine environment.

In general, modern desalination plants in the Gulf region have

sound designs for their intake and outfall, to avoid recycling of

discharged effluents into the feed water intakes. The collective

environmental risk of the pollutants constituting the brine water

discharged to the near-shore marine environment might be mani-

fested in one or more of the following forms:

Physical risk

– Resulting from the discharge of hot brine from

thermal desalination.

Chemical risk

– Resulting from chemical agents remaining in

the brine water and added within the process for the control of

bio-fouling, scale formation and foaming. Additionally, seawater

reverse osmosis (RO) necessitates an exhaustive pre-treatment of

the feed water to avoid accelerated fouling and scaling of the RO

membranes. This pre-treatment involves pre-chlorination, coag-

ulation using coagulants and coagulant aids, sedimentation,

clarification, sand filtration and dechlorination before conveyance

to the RO membranes.

Biological risk

– The secondary effect of oxygen demand exerted

by natural and induced organics in the brine water. Relatively

higher levels of biochemical oxygen demand (BOD) might be

observed in the desalination plant effluents. The impact of BOD

demand for dissolved oxygen (DO), associated with lower levels

of DO in brine water due to higher salt content and temperature,

will ultimately reduce the level of DO in seawater adjacent to the

brine water out-falls.

Desalination as a potential technological

hazard to the environment in the arid

Western Asia region

Hosny Khordagui PhD, Chief, Water & Environment Team,

UN Economic and Social Commission for Western Asia