Evaluating the Effect of Producing Desalinated Seawater on Hypersaline Arabian Gulf

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1 European Journal of Scientific Research ISSN X Vol.22 No.2 (2008), pp EuroJournals Publishing, Inc Evaluating the Effect of Producing Desalinated Seawater on Hypersaline Arabian Gulf H.H. Al Barwani Department of Mathematics and Statistics, College of Science,Sultan Qaboos University P.O. Box 36, Al-Khod 123, Muscat, Oman Tel: + (968) ; Fax: + (968) Anton Purnama Department of Mathematics and Statistics, College of Science,Sultan Qaboos University P.O. Box 36, Al-Khod 123, Muscat, Oman antonp@squ.edu.om Tel: + (968) ; Fax: + (968) Abstract The Arabian Gulf is the main source for desalinated seawater to make up deficiencies in the supplies of potable water for Kuwait, Saudi Arabia, Bahrain, Qatar, and the United Arab Emirates. Due to its semi-enclosed nature and arid climate of the bordering lands, seawater in the Arabian Gulf can have an extremely high evaporation rate leading to hypersaline conditions. Therefore, any further loss of water by desalination plants would deteriously change the salinity. The impact of seawater desalination on the salinity of the Arabian Gulf is evaluated using a mathematical model. Due to the exponential sensitivity to the plant s location and its water production rate, the effect of a plant located close to the head of the Gulf is found to be more severe. Keywords: Arabian Gulf, Hypersaline, Mathematical model, Seawater desalination, Semi-enclosed sea Introduction The water shortage in the arid climate of the Arabian Gulf countries has reached unprecedented crisis levels. The demand for water is ever increasing as the consequences of rapid industrial development and population growth, with a mean annual increase rate of 8% (Darwish and Al Najem, 2005; Hashim and Hajjaj, 2005). In 2002 the Arabian Gulf countries average rate of water consumption was estimated at 400 l/d per capita (Dawoud, 2005). As drought conditions worsen, almost all the existing underground water resources have been developed and are being exploited at an unsustainable rate. Therefore, to alleviate water shortages and avert the real threat to resource sustainability, the Arabian Gulf countries are making continuous efforts to produce water by constructing desalination plants. Once a desalination plant is built, its daily water production rate will subsequently be increased in line with the projected demands. In fact, desalinated seawater is the major water supply for Kuwait (Darwish and Al Najem, 2005), the United Arab Emirates (Sommariva and Syambabu, 2001), Qatar

2 Evaluating the Effect of Producing Desalinated Seawater on Hypersaline Arabian Gulf 280 (Amer and Al Rahman, 2005) and Bahrain (Hashim and Hajjaj, 2005), and counts for at least half of the supplies in Saudi Arabia (Dawoud, 2005). The unwanted by-product of desalination processes is brine, a highly concentrated salt solution up to two times the seawater salinity. The distillation process can achieve a recovery of product water up to 50% from seawater (Hajeeh and Al Othman, 2005), and the continuous discharge into the Arabian Gulf is the practical method used to dispose of brine waste stream from a desalination plant (Areiqat and Mohamed, 2005). The present daily total of installed desalination capacity of plants operated in the Arabian Gulf was estimated at more than 10 million m 3 (Figure 1). The large plants in terms of daily production capacities are Al Jubail with 2.01 million m 3 on the coast of Saudi Arabia; Al Taweelah with 1.06 million m 3, Um Al Nar with 0.86 million m 3 and Shuweihat with 0.45 million m 3 on the coast of Abu Dhabi; Jebel Ali with 1.17 million m 3 on the coast of Dubai; and AzZour and Doha (east) both with 0.5 million m 3 on the coast of Kuwait. Assuming a 50% recovery ratio, all together the desalination plants operating in the Arabian Gulf are discharging their brine waste in excess of 10 million m 3 per day into the Gulf (Hashim and Hajjaj, 2005). Figure 1: Quantity of desalinated seawater produced from the Arabian Gulf. The Arabian Gulf is a shallow semi-enclosed sea connected to the Gulf of Oman via the narrow Strait of Hormuz (Figure 2), with a mean depth of 35 m (Reynolds, 1993). It covers an area of about km 2, and is 1000 km in length with widths ranging from 185 to 340 km. The freshwater inflows from the Tigris, the Euphrates and the Karun at the delta of the Shatt al Arab were estimated at 0.18 m/yr (Chao et al., 1992). Seawater in the Gulf is naturally characterized by higher salt content due to high evaporation with an annual mean rate of 2.0 m/yr (Meshal and Hassan, 1986), where surface salinity values exceeding 40 ppt were recorded, especially in the shallow waters around the island of Bahrain (Burashid and Hussain, 2004) and the coasts of Qatar and the United Arab Emirates (Brewer and Dyrssen, 1985; Reynolds, 1993; Mohamed et al., 2004). To assess how seawater desalination plants operated along the coast of Arabian Gulf would increase the salinity, a mathematical model is developed using a simple channel geometry representation of the semi-enclosed sea (Purnama et al., 2005). As the impact of desalination plants on seawater depends exponentially on the plant s location and its volumetric rate of seawater extraction, special attention should be given to the long-term seawater desalination planning and management (Hoepner, 1999; Schiffler, 2004).

3 281 H.H. Al Barwani and Anton Purnama Figure 2: ocation of large desalination plants in the Arabian Gulf. Mathematical model Following Purnama et al. (2005), the Arabian Gulf is modeled as a semi-enclosed sea joining to the open sea at x = (Figure 3), where the channel width and depth are specified by B( x) = ( 3 B 2 ) x and H ( x) = ( 2 H ) x, respectively (Smith, 1977). As the open sea is the main source of water for the semi-enclosed sea, A x 0 ( x) U ( x) = U B( z)dz where A = B H is the cross-sectional area, U is the incoming current and U is the rate of change of water depth. Figure 3: The channel geometry of a semi-enclosed sea. The equation of mass flux of water is a balance between the incoming current U from the open sea and the freshwater input F from the head of the semi-enclosed sea, with the continuous depletion by evaporation at the rate μ and the water production rate rq by a desalination plant located at x = a i : i

4 Evaluating the Effect of Producing Desalinated Seawater on Hypersaline Arabian Gulf 282 d dx ( AU F ) = μ B rq δ ( x ) n i = 1 i a i where r 0. 5 is the plant s recovery ratio and δ is the Dirac delta function. Next, if the operated desalination plants are continuously discharging their brine waste stream, then the advection-diffusion equation for the salinity s is given by n d d ds ( AUs) AD = Qi sδ ( x a i ) dx dx dx i = 1 2 where the longitudinal shear dispersion coefficient D = αb U H On integrating the equations, and matching the salinity to s at x =, the logarithm of relative salinity increase Δ s due to seawater desalination plants can be evaluated from (Purnama et al., 2005) n Δs dz ln 1 + = ( 1 + r) Qi s i = 1 ( x ai ) AD max, where s is the maximum salinity. The salinity increase in the Arabian Gulf The model parameter α U could be determined by matching the salinity to the measured surface salinity in the Arabian Gulf, with s = 37 ppt at the Strait of Hormuz, and the maximum surface salinity was reported to be s = 42 ppt (Chao et al., 1992) and s = 45 ppt (Hashim and Hajjaj, 2005; Mohamed et al., 2004). For illustrations, typical values relevant to the Arabian Gulf are B = 240 km, H = 35 m, = 1000 km, the annual mean evaporation rate μ = 2 m/yr and the river discharge F = 44km 3 /yr. Thus, the model parameter is estimated at α U m/yr for s = 42 ppt and α U m/yr for s = 45 ppt. The salinity increase Δ s due to a desalination plant located at x = a with q = ( 1 + r) Q F is given by x a β q 1, < a Δs ln 1 + = s a x q β 1, x where the maximum salinity occurs at x ( q) 2 3 1, with β for s = 42 ppt and β for s = 45 ppt. Using r = 0. 4, the salinity increase in the Arabian Gulf due to a desalination plant operated at x = a is shown in Figure 4. For example with s = 45 ppt (Figure 4b), the impact of Al Jubail plant with q = located at a is roughly equivalent to Δs ppt. However, if the production rate were to increase up to 5 q then its impact would increase to Δs 0.57 ppt.

5 283 H.H. Al Barwani and Anton Purnama Figure 4: Salinity increase due to a plant operated at x = a : a) s 42 ppt and b) s 45 ppt. = = The impact of a desalination plant located near the head of the Arabian Gulf is found to be more severe than those that are located near the mouth of the Gulf. Thus using s = 42 ppt (Figure 4a), a plant operated at a = 0. 2 with q = would have the same maximum salinity increase of 0.25 ppt as a plant operated at a = 0. 6 but with more than four times its production rate, i.e. q Finally, assuming that all desalination plants operated in the Arabian Gulf are represented by three large plants, with the first plant located at a = 0. 1 with q = 0. 05, the second at a = 0. 5 with q = 0.14 and the third at a = 0. 8 with q = 0. 12, then the distribution of salinity increase Δ s s due to seawater desalination in the Arabian Gulf is shown in Figure 5. Assuming s = 45 ppt, the impact of producing desalinated seawater would be the salinity increase Δs 0. 3 ppt inland of the first plant, Δs 0.22 ppt inland of the second plant and Δs 0. 1 ppt inland the third plant. Figure 5: Salinity increase due to desalination plants in the Arabian Gulf. Conclusion A desalination plant s reliability and service availability are essential to sustain and allow the continuing long-term socio-economic development in the Arabian Gulf countries. Regrettably, as desalinated seawater is indispensably required at any cost, the main concern so far has been limited on

6 Evaluating the Effect of Producing Desalinated Seawater on Hypersaline Arabian Gulf 284 the potential impact of off shore oil spills on desalination plants (Al Malek and Mohamed, 2005). Due to its semi-enclosed nature and arid climate, special attention should also be given to the impact of seawater desalination plants on the hypersaline Arabian Gulf (Hoepner, 1999; Schiffler, 2004). essons from the exploitation of the groundwater resources should have been learned so that meeting the water demands should not be at the expense of the Arabian Gulf s fragile environment (Hashim and Hajjaj, 2005). Higher salinity of the seawater intake will reduce the desalination plant s efficiency (Abdul Azis et al., 2000), and hence increase the cost of producing desalinated seawater (Dore, 2005). The unfortunate example is the Addur reverse osmosis desalination plant in the southern part of Bahrain, where the harsh seawater conditions brought down the plant s production capacity to less than half the installed capacity (Burashid and Hussain, 2004). Acknowledgement This work was supported by the Internal Grant at Sultan Qaboos University under the research project code IG/SCI/DOMS/05/07. References [1] Abdul Azis, P.K., Al Tisan, I., Al Daili, M., Green, T.N., Dalvi, A.I. and Javeed, M.A. (2000) Effects of environment on source water for desalination plants on the eastern coast of Saudi Arabia. Desalination 132: [2] Al Malek, S.A. and Mohamed, A.M.O. (2005) Environmental impact assessment of off shore oil spill on desalination plant. Desalination 185: [3] Amer, K.M. and Al Rahman, M.A. (2005) Water resources management and development to combat water scarcity in Qatar. Arab Water World 29(6): [4] Areiqat, A. and Mohamed, K.A. (2005) Optimization of the negative impact of power and desalination plants on the ecosystem. Desalination 185: [5] Brewer, P.G. and Dyrssen, D. (1985) Chemical oceanography of the Persian Gulf. Prog. Oceanogr. 14: [6] Burashid, K. and Hussain, A.R. (2004) Seawater RO plant operation and maintenance experience: Addur desalination plant operation assessment. Desalination 165: [7] Chao, S-Y., Kao, T.W. and Al Hajri, K.R. (1992) A numerical investigation of circulation in the Arabian Gulf. J. Geophys. Res. 97: [8] Darwish, M.A. and Al Najem, N. (2005) The water problem in Kuwait. Desalination 177: [9] Dawoud, M.A. (2005) The role of desalination in augmentation of water supply in GCC countries. Desalination 186: [10] Dore, M.H.I. (2005) Forecasting the economic costs of desalination technology. Desalination 172: [11] Hajeeh, M. and Al Othman, A. (2005) Application of the analytical hierarchy process in the selection of desalination plants. Desalination 174: [12] Hashim, A. and Hajjaj, M. (2005) Impact of desalination plants fluid effluents on the integrity of seawater, with the Arabian Gulf in perspective. Desalination 182: [13] Hoepner, T. (1999) A procedure for environmental impact assessments (EIA) for seawater desalination plants. Desalination 172: [14] Meshal, A.H. and Hassan, H.M. (1986) Evaporation from the coastal water of the central part of the Gulf. Arab Gulf J. Scient. Res. 4: [15] Mohamed, K.A., Arieqat, A. and Odeh, M. (2004) Set-up of a mid-field model to investigate the circulation of effluents in the Mirfa power and desalination plant. Desalination 166:

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