- Email: [email protected]
The structural safety of connections with fillet welds
Desalination 182 (2005) 395–402
Preliminary results of the monitoring of the brine discharge produced by the SWRO desalination plant of Alicante (SE Spain) Y. Ferna´ndez-Torquemada*, J.L. Sa´nchez-Lizaso, J.M. Gonza´lez-Correa Unidad de Biologı´a Marina, Dpto. de Ciencias del Mar y Biologı´a Aplicada, Universidad de Alicante. Apdo. 99, E. 03080, Spain Tel. þ34 965 903400x2916; Fax þ34 965 903815; email: [email protected] Received 9 February 2005; accepted 10 March 2005
Abstract Data from monitoring of the dispersion and effects of the hypersaline effluents originated by desalination plants are very scarce. The objective of this paper is to present the monitoring, on time and space, of the brine discharge originated by the Alicante seawater desalination plant (SE Spain). Since the seawater reverse osmosis (SWRO) desalination plant started to operate in September 2003, to the date, three campaigns were made in order to determine the seasonal and spatial distribution of the brine plume and its dilution along the area. One year after the plant operation, the results obtained at these campaigns have shown that dilution of the brine may be lower than the usually accepted and it may affect significant extensions of marine communities. Due to the recent development of the desalination activity in our country the information obtained in this work can be considered really useful for its application to future similar projects in the Mediterranean Sea. Keywords: Desalination; Brine discharge; Environmental impact; Monitoring; Posidonia oceanica; Echinoderms
1. Introduction Desalination in Mediterranean countries is a steadily growing industry, where seawater desalination by reverse osmosis (SWRO) has become the most extended method due to its reduced inversion costs and its lower energy
and space consumption [1]. However, this activity may result on environmental impacts mainly generated from the discharge into the sea of the brine produced (44–90 psu), and also from the chemicals (anti-scalant, antifouling, hydrochloric acid, sodium hexametaphosphate, etc.) Used in desalination processes [2,3]. There are different options for the
*Corresponding author. Presented at the Conference on Desalination and the Environment, Santa Margherita, Italy, 22–26 May 2005. European Desalination Society. 0011-9164/05/$– See front matter Ó 2005 Elsevier B.V. All rights reserved doi:10.1016/j.desal.2005.03.023
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disposal brine [4–8], but ocean brine disposal is considered the least expensive one [7,9]. If the brine is discharged into the sea, the density difference between brine and seawater induce the formation of a stratified system, with the brine forming a bottom layer that can affect the benthic communities habituated to stable salinity environments [9–13]. The magnitude of this impact will depend on the characteristics of the desalination plant and its reject brine, but also on the nature of the physical (i.e., Bathymetry, hydrodynamics, etc.) And biological conditions of the receiving marine environment [6,9,14]. Although the number of scientific publications dealing with the issue are limited [3,15–17], the discharge of brine into the sea requires particular attention and scientific assessment of possible impacts on the marine environment.
The main objective of the present study is to determine the seasonal and spatial distribution of the brine discharge from the SWRO desalination plant of Alicante during its first year of operation and to quantify the potential impact associated with this discharge on the Posidonia oceanica meadows and echinoderm communities present in the area.
2. Materials and methods 2.1. Location and description of the desalination plant The study area (Fig. 1) was located at Alicante (SE Spain), where a seawater reverse osmosis (SWRO) desalination plant started to work in September 2003. It has a capacity of
Fig. 1. Location of the Alicante SWRO desalination plant and situation of the three stations employed for the monitoring of the biological communities.
Y. Ferna´ndez-Torquemada et al. / Desalination 182 (2005) 395–402
50,000 m3/d with a conversion factor of 40%. This represents a discharge of 75,000 m3/d with a salinity of 68 psu. Income water was obtained from beach wells. Discharge is produced on the shore South of Alicante Harbour since this is an area degraded by previous impacts (seawages, harbour, mooring, . . . ). 2.2. Field campaigns and data acquisition Three surveys have been done in February, April and August 2004. In each campaign a grid of more than 100 sampling stations near the brine discharge place was established, with the purpose of delimiting the brine plume and its dilution along the area. At each station salinity measures were taken from surface and bottom water. It was utilized a RBR CTD, with a measuring range of 0–70 psu and a resolution 0.01 psu. Each station was positioned using a GPS Garmin 50 (precision 5 m). After the results of the first survey we decided to extend the grid to cover a larger area. 2.3. Spatial data representation An interpolation of the data obtained in each campaign was made using the kriging technique, with the purpose of getting a real representation of the salinity variable in the space. Before using this methodology, it must be probed some kind of spatial correlation between data. For this reason it was utilized the geoeas (Geostatistical Environmental Assessment Software) program developed by the US Environmental Protection Agency (EPA). With this program we obtained the experimental variogram, the model that better fits to it (subprogram VARIO) and its validation (subprogram VALID). Then the obtained model was used with the Surfer v.7 program (Golden Software Inc., Golden, Colorado) to get the graphical spatial
397
representation of deep and salinity data in the studied area. 2.4. Monitoring of biological communities Biological organisms selected included both, Posidonia oceanica meadows, due to their ecological relevance, and echinoderms, due to their sensitiveness to changes in salinity. Three stations have been selected; one in front of the desalination plant discharge, and two controls, one two kilometers North, in front of Alicante Harbour, and the other one two kilometers South, in front of Urbanova Beach (Fig. 1). At each station 12 microcartography quadrats were established in June 2003 at the upper limit of the meadow (16 m depth) and at the continuous meadows (20 m depth). Each quadrat was a 40 40 cm frame inside of which all Posidonia shoots were marked. Survey of quadrats was done in February and August 2004 to estimate new and dead shoots. Density of echinoderms was estimated at the same localities but only in the upper limit of the meadow with 10 replicates of 10 m2 in June 2003 and in February and August 2004. 3. Results Vertical profiles obtained at the different surveys in the locality in front of the discharge at 16 m depth (2000 m from the discharge) are shown in Fig. 2. During the surveys of February and April, maximum salinity was observed at the bottom. In August, maximum salinity was observed at the termocline level. This is the consequence of the low temperature under the termocline, which produced that the density under the termocline was higher that at the brine level. Surface salinity is homogeneous and has no clear trend at any survey (Figs. 3a, 4a and 5a) Dispersion of the brine at the bottom is represented in Fig. 3b for the February
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Depth (m)
Temperature (ºC) 13.5 0 2 4 6 8 10 12 14 16 18
14 February
Depth (m)
14.9
15
18 20 22 24 0
6 8 10 12
37.5
38
A
38.5
39 Salinity
37
B
37.5
38
38.5
39
0 2 4 6 8 10 12 14 16 18
4 6 8 10 12 14 16 18
2 4
37 0 2 4 6 8 10 12 14 16 18
14.7 14.8 0 April 2
Depth (m)
Salinity 14.5
26 28
41.6 41.4 41.2 41 40.8 40.6 40.4 40.2 40 39.8 39.6 39.4 39.2 39 38.8 38.6 38.4 38.2 38 37.8 37.6 37.4 37.2
Fig. 3. Spatial representation of salinity distribution on the surface (a) and on the bottom (b) obtained in February 2004. 37
37.5
38
38.5
39
0 August
2 4 6 8 10 12
14 16
14
18
18
16
Fig. 2. Temperature and salinity vertical profiles obtained at the different surveys in one point inside the Posidonia oceanica meadow.
survey. The dilution close to the discharge is very fast but a high stability could be found far from the discharge. It is possible to observe an increase higher that 0.5 psu above average salinity in the area up to 4 km from the discharge. After these results we increase the area to cover in the following
surveys. In Fig. 4 results of the April survey are presented. The same trend is observed, a high dilution in the near field and a very low dilution in the far field (Fig. 4b). Brine dispersal follows the bathymetry and spread as it moves away from the discharge point. Significant increases of salinity at the bottom are observed several kilometers away from the discharge point. Salinity increases reach to all the deep localities (20 m) and to most of the shallow (16 m) localities with the exception of the northern one. Results in the August survey (Fig. 5) are different since maximum salinity was not found at the bottom. At the bottom (Fig. 5b) salinity increase is observed only during the first hundreds of meters which may produce an incorrect feeling of dilution. At the termocline level, where maximum salinity is observed, the same pattern than in previous surveys was found (Fig. 5c).
399
Y. Ferna´ndez-Torquemada et al. / Desalination 182 (2005) 395–402 A
A Salinity
B
41.6 41.4 41.2 41 40.8 40.6 40.4 40.2 40 39.8 39.6 39.4 39.2 39 38.8 38.6 38.4 38.2 38 37.8 37.6 37.4 37.2
Salinity
B
C
Fig. 4. Spatial distribution of salinity on the surface (a) and on the bottom (b) during the campaign of April 2004.
Echinoderms have disappeared from the meadow in front of the desalination plant and Urbanova (southern locality) after the impact (Fig. 6). At the northern locality (Alicante Harbour) an important increment is observed in February followed by a decrease to lower values than before the operation of the desalination plant. These results are coherent with the dispersion of the brine since the northern locality is the less affected by the brine. Survey of Posidonia oceanica shows, at all the localities, that the number of new shoots
41.6 41.4 41.2 41 40.8 40.6 40.4 40.2 40 39.8 39.6 39.4 39.2 39 38.8 38.6 38.4 38.2 38 37.8 37.6 37.4 37.2
Fig. 5. Representation of the superficial (a), bottom (b) and the maximum salinities (c) obtained at August 2004.
produced between June 2003 and August 2004 is higher than the number of dead
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2004 W
16 m
20
2004 S
20 m
18
0.6 Shoot division rate (%)
Density of echinoderms (ind/m2)
0.7
0.5 0.4 0.3 0.2 0.1
16 14 12 10 8 6 4 2
0 Harbour
Urbanova
0
Desalination plant
Harbour
Urbanova 16 m 20 m
Desalination plant
Harbour
Urbanova 16 m 20 m
Desalination plant
Harbour
Urbanova
Desalination plant
5
shoots and, consequently, shoot balance is positive (Fig. 7). However, the higher vitality is observed at the northern locality and the lower vitality in the meadows in front of the desalination plant discharge. 4. Discussion The place for the brine disposal of the Alicante desalination plant was chosen because the area was seriously damaged due to the expansion of the Alicante Harbour and several seawages that have produced the regression of Posidonia oceanica meadows. Before the desalination plant starts to operate in September 2003, P. Oceanica meadows appeared at 16 m depth and about 2 km from the disposal point. Our results showed that dilution was lower that what has been foreseen. Near the discharge point dilution is very strong but a layer of water of high density expands over the bottom to a distance of several kilometers. This low dilution is observed also in August when, due to the low temperature of water below termocline, the brine moves in the middle of the water column. However this situation is more
Shoot mortality rate (%)
4.5 4 3.5 3 2.5 2 1.5 1 0.5 0 18 16 14 Shoot balance (%)
Fig. 6. Mean values (and standard errors) of the density of echinoderms (individuals per m2) in the station closest to the desalination plant discharge and the two controls (Urbanova Beach and Alicante Harbour) during Summer 2003, Winter 2004 and Summer 2004.
12 10 8 6 4 2 0
Fig. 7. Division and mortality rates of the Posidonia oceanica shoots in the station closest to the desalination plant discharge and the two controls (Urbanova Beach and Alicante Harbour).
positive for benthic organisms that are not affected by higher salinities. Echinoderms have been chosen because they are osmoconformers organisms, which are not able to regulate their osmotic pressure. Several studies have demonstrated that they are only able to tolerate a narrow range of salinities. The disappearance of the echinoderms in the area of the brine influence may
Y. Ferna´ndez-Torquemada et al. / Desalination 182 (2005) 395–402
be used as an indicator of changes in the marine communities produced by the brine disposal of desalination plant. The temporal increase of echinoderms in the northern locality may be related with their movement away from the brine. Posidonia oceanica meadows are important communities in the Mediterranean Sea from an economic and ecological point of view and are protected in the entire basin. They are very sensitive to human activities and their regression is common in many locations of the Mediterranean. Recently it has been demonstrated the low tolerance of this species to salinity increments [18,19]. Salinity increments measured at the meadow in front of the desalination plant discharge are close to the ones that have produced significant effects on their growth and survival. Preliminary results obtained show that, during the first year of monitoring, the desalination plant has not produced the regression of the meadow but it has affected the vitality of the plants. The higher vitality has been observed in the northern locality, which is the less affected by the brine but the more affected by other sources of pollution. Our results show that dilution of the brine from a RO desalination plant may be lower than the usually accepted and may affect important extensions of marine communities. In order to minimize the impact of desalination plants it is important to select a correct location of the plants and to maximize the dilution of its brine. This may be achieved using a previous dilution of the brine with seawater that has been proved useful in other plants [20,21]. Acknowledgements We thank Just Bayle Sempere who assisted in the winter campaign of 2004. We also would like to thank Marina of Alicante for
401
use of equipment and facilities. This work was funded by UTE Desaladora de Alicante and Mancomunidad de Canales del Taibilla and by a FPI grant from the Generalitat Valenciana (FPI 01 A 002). References [1] A.J. Morton, I.K. Callister and N.M. Wade, Environmental impacts of seawater distillation and reverse osmosis processes. Desalination, 108 (1996) 1–10. [2] T. Ho¨pner and J. Windelberg, Elements of environmental impact studies on coastal desalination plants. Desalination 108 (1996) 11–18. [3] J.L. Pe´rez Talavera and J.J. Quesada Ruiz, Identification of the mixing processes in brine discharges carried out in Barranco del Toro Beach, south of Gran Canaria (Canary Islands). Desalination 139 (2001) 277–286. [4] P. Glueckstern and M. Priel, Optimized brackish water desalination plants with minimum impact on the environment. Desalination 108 (1996) 19–26. [5] D. Squire, J. Murrer, P. Holden and C. Fitzpatrick, Disposal of reverse osmosis membrane concentrate. Desalination 108 (1996) 143–147. [6] M. Ahmed, W.H. Shayya, D. Hoey, A. Mahendran, R. Morris and J. Al-Handaly, Use of evaporation ponds for brine disposal in desalination plants. Desalination 130 (2000) 155–168. [7] M. Ahmed, W.H. Shayya, D. Hoey and J. Al-Handaly, Brine disposal from reverse osmosis desalination plants in Oman and the United Arab Emirates. Desalination 133 (2001) 135–147. [8] M. Ahmed, A. Arakel, D. Hoey, M.R. Thumarukudy, M.F.A. Goosen, M. Al-Haddabi and A. Al-Belushi, Feasibility of salt production from inland RO desalination plant reject brine: a case study. Desalination 158 (2003) 109–117. [9] S. Lattemann and T. Ho¨pner, Seawater desalination. Impacts of Brine and Chemical Discharges on the Marine Environment, Desalination Publications, L’Aquila, Italy, 2003. [10] J.V. Del Bene, G. Jirka and J. Largier, Ocean brine disposal. Desalination 97 (1994) 365–372. [11] E. Gacia and E. Ballesteros, El impacto de las plantas desalinizadoras sobre el medio marino:
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la salmuera en las comunidades bento´nicas mediterra´neas. in: Conferencia Internacional: El Plan Hidrolo´gico Nacional Y la Gestio´n Sostenible Del Agua. Aspectos medioambientales, reutilizacio´n y desalacio´n, Zaragoza, Junio 2001, 10pp. [12] R. Einav and F. Lokiec, Environmental aspects of a desalination plant in Ashkelon. Desalination 156 (2003) 79–85. [13] A. Purnama, H.H. Al-Barwani and M. Al-Lawatia, Modeling dispersion of brine waste discharges from a coastal desalination plant, Desalination 155 (2003) 41–47. [14] R. Einav, R. K. Harussi and D. Perry, The footprint of the desalination processes on the environment. Desalination 152 (2002) 141–154. [15] R.H. Chesher, Biological impact of a large-scale desalination plant at Key West, Florida. in: Tropical Marine Pollution, E.J. Ferguson and R.E. Johanes, eds., Elsevier Scientific Publishing Company, Amsterdam, 1975, pp. 99–81. [16] D.A. Tomasko, N.J. Blake, C.W. Dye and M.A. Hammond, Effects of the disposal of reverse osmosis seawater desalination discharges on a seagrass meadow (Thalassia testudinum) offshore of Antigua, West Indies. in: Seagrasses: Monitoring, Ecology, Physiology and Management, 1999, pp. 99–112. [17] L. Castriota, C¸.M. Beltrano, O. Giambalvo, P. Vivona and G. Sunseri, A one-year study of the effects of a hyperhaline discharge from a
desalination plant on the zoobenthic communities in the Ustica Island Marine Reserve (Southern Tyrrhenian Sea). in: CIESM, 2001. [18] J.L. Buceta, Y. Ferna´ndez-Torquemada, E. Gacı´ a, O. Invers, J. Mas, J. Romero, J.M. Ruiz, A. Ruiz-Mateo, S. Sabah and J.L. Sa´nchez-Lizaso, Investigacio´n conjunta sobre la tolerancia de Posidonia oceanica a incrementos de salinidad. Ingenierı´ a Civil 132 (2003) 111–116. [19] Y. Ferna´ndez-Torquemada and J.L. Sa´nchezLizaso, Effects of salinity on leaf growth and survival of the Mediterranean seagrass IPosidonia oceanicaX (L.) Delile. Journal of Experimental Marine Biology and Ecology, 2005. [20] J.L. Sa´nchez Lizaso, Y. Ferna´ndez Torquemada, J.M. Gonza´lez Correa, A. Carratala´ Gime´nez, C. Valle, A. Forcada and F. Cano, Resultados del programa de vigilancia ambiental de la IDAM de Ja´vea (Alicante). V Congreso Nacional AEDyR. La Desalacio´n En El Sur Del Mediterra´neo, Almeria, Noviembre 2004. [21] Y. Ferna´ndez Torquemada, J.M. Gonza´lez Correa and J.L. Sa´nchez Lizaso, Medidas de atenuacio´n del posible impacto ambiental del vertido de las desaladoras de osmosis inversa: E1 Ejemplo de Ja´vea (Alicante). IV. Congreso Ibe´rico Sobre Gestio´n Y Planificacio´n Del Agua, Tortosa, Diciembre 2004.
Preliminary results of the monitoring of the brine discharge produced by the SWRO desalination plant of Alicante (SE Spain) Y. Ferna´ndez-Torquemada*, J.L. Sa´nchez-Lizaso, J.M. Gonza´lez-Correa Unidad de Biologı´a Marina, Dpto. de Ciencias del Mar y Biologı´a Aplicada, Universidad de Alicante. Apdo. 99, E. 03080, Spain Tel. þ34 965 903400x2916; Fax þ34 965 903815; email: [email protected] Received 9 February 2005; accepted 10 March 2005
Abstract Data from monitoring of the dispersion and effects of the hypersaline effluents originated by desalination plants are very scarce. The objective of this paper is to present the monitoring, on time and space, of the brine discharge originated by the Alicante seawater desalination plant (SE Spain). Since the seawater reverse osmosis (SWRO) desalination plant started to operate in September 2003, to the date, three campaigns were made in order to determine the seasonal and spatial distribution of the brine plume and its dilution along the area. One year after the plant operation, the results obtained at these campaigns have shown that dilution of the brine may be lower than the usually accepted and it may affect significant extensions of marine communities. Due to the recent development of the desalination activity in our country the information obtained in this work can be considered really useful for its application to future similar projects in the Mediterranean Sea. Keywords: Desalination; Brine discharge; Environmental impact; Monitoring; Posidonia oceanica; Echinoderms
1. Introduction Desalination in Mediterranean countries is a steadily growing industry, where seawater desalination by reverse osmosis (SWRO) has become the most extended method due to its reduced inversion costs and its lower energy
and space consumption [1]. However, this activity may result on environmental impacts mainly generated from the discharge into the sea of the brine produced (44–90 psu), and also from the chemicals (anti-scalant, antifouling, hydrochloric acid, sodium hexametaphosphate, etc.) Used in desalination processes [2,3]. There are different options for the
*Corresponding author. Presented at the Conference on Desalination and the Environment, Santa Margherita, Italy, 22–26 May 2005. European Desalination Society. 0011-9164/05/$– See front matter Ó 2005 Elsevier B.V. All rights reserved doi:10.1016/j.desal.2005.03.023
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disposal brine [4–8], but ocean brine disposal is considered the least expensive one [7,9]. If the brine is discharged into the sea, the density difference between brine and seawater induce the formation of a stratified system, with the brine forming a bottom layer that can affect the benthic communities habituated to stable salinity environments [9–13]. The magnitude of this impact will depend on the characteristics of the desalination plant and its reject brine, but also on the nature of the physical (i.e., Bathymetry, hydrodynamics, etc.) And biological conditions of the receiving marine environment [6,9,14]. Although the number of scientific publications dealing with the issue are limited [3,15–17], the discharge of brine into the sea requires particular attention and scientific assessment of possible impacts on the marine environment.
The main objective of the present study is to determine the seasonal and spatial distribution of the brine discharge from the SWRO desalination plant of Alicante during its first year of operation and to quantify the potential impact associated with this discharge on the Posidonia oceanica meadows and echinoderm communities present in the area.
2. Materials and methods 2.1. Location and description of the desalination plant The study area (Fig. 1) was located at Alicante (SE Spain), where a seawater reverse osmosis (SWRO) desalination plant started to work in September 2003. It has a capacity of
Fig. 1. Location of the Alicante SWRO desalination plant and situation of the three stations employed for the monitoring of the biological communities.
Y. Ferna´ndez-Torquemada et al. / Desalination 182 (2005) 395–402
50,000 m3/d with a conversion factor of 40%. This represents a discharge of 75,000 m3/d with a salinity of 68 psu. Income water was obtained from beach wells. Discharge is produced on the shore South of Alicante Harbour since this is an area degraded by previous impacts (seawages, harbour, mooring, . . . ). 2.2. Field campaigns and data acquisition Three surveys have been done in February, April and August 2004. In each campaign a grid of more than 100 sampling stations near the brine discharge place was established, with the purpose of delimiting the brine plume and its dilution along the area. At each station salinity measures were taken from surface and bottom water. It was utilized a RBR CTD, with a measuring range of 0–70 psu and a resolution 0.01 psu. Each station was positioned using a GPS Garmin 50 (precision 5 m). After the results of the first survey we decided to extend the grid to cover a larger area. 2.3. Spatial data representation An interpolation of the data obtained in each campaign was made using the kriging technique, with the purpose of getting a real representation of the salinity variable in the space. Before using this methodology, it must be probed some kind of spatial correlation between data. For this reason it was utilized the geoeas (Geostatistical Environmental Assessment Software) program developed by the US Environmental Protection Agency (EPA). With this program we obtained the experimental variogram, the model that better fits to it (subprogram VARIO) and its validation (subprogram VALID). Then the obtained model was used with the Surfer v.7 program (Golden Software Inc., Golden, Colorado) to get the graphical spatial
397
representation of deep and salinity data in the studied area. 2.4. Monitoring of biological communities Biological organisms selected included both, Posidonia oceanica meadows, due to their ecological relevance, and echinoderms, due to their sensitiveness to changes in salinity. Three stations have been selected; one in front of the desalination plant discharge, and two controls, one two kilometers North, in front of Alicante Harbour, and the other one two kilometers South, in front of Urbanova Beach (Fig. 1). At each station 12 microcartography quadrats were established in June 2003 at the upper limit of the meadow (16 m depth) and at the continuous meadows (20 m depth). Each quadrat was a 40 40 cm frame inside of which all Posidonia shoots were marked. Survey of quadrats was done in February and August 2004 to estimate new and dead shoots. Density of echinoderms was estimated at the same localities but only in the upper limit of the meadow with 10 replicates of 10 m2 in June 2003 and in February and August 2004. 3. Results Vertical profiles obtained at the different surveys in the locality in front of the discharge at 16 m depth (2000 m from the discharge) are shown in Fig. 2. During the surveys of February and April, maximum salinity was observed at the bottom. In August, maximum salinity was observed at the termocline level. This is the consequence of the low temperature under the termocline, which produced that the density under the termocline was higher that at the brine level. Surface salinity is homogeneous and has no clear trend at any survey (Figs. 3a, 4a and 5a) Dispersion of the brine at the bottom is represented in Fig. 3b for the February
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Depth (m)
Temperature (ºC) 13.5 0 2 4 6 8 10 12 14 16 18
14 February
Depth (m)
14.9
15
18 20 22 24 0
6 8 10 12
37.5
38
A
38.5
39 Salinity
37
B
37.5
38
38.5
39
0 2 4 6 8 10 12 14 16 18
4 6 8 10 12 14 16 18
2 4
37 0 2 4 6 8 10 12 14 16 18
14.7 14.8 0 April 2
Depth (m)
Salinity 14.5
26 28
41.6 41.4 41.2 41 40.8 40.6 40.4 40.2 40 39.8 39.6 39.4 39.2 39 38.8 38.6 38.4 38.2 38 37.8 37.6 37.4 37.2
Fig. 3. Spatial representation of salinity distribution on the surface (a) and on the bottom (b) obtained in February 2004. 37
37.5
38
38.5
39
0 August
2 4 6 8 10 12
14 16
14
18
18
16
Fig. 2. Temperature and salinity vertical profiles obtained at the different surveys in one point inside the Posidonia oceanica meadow.
survey. The dilution close to the discharge is very fast but a high stability could be found far from the discharge. It is possible to observe an increase higher that 0.5 psu above average salinity in the area up to 4 km from the discharge. After these results we increase the area to cover in the following
surveys. In Fig. 4 results of the April survey are presented. The same trend is observed, a high dilution in the near field and a very low dilution in the far field (Fig. 4b). Brine dispersal follows the bathymetry and spread as it moves away from the discharge point. Significant increases of salinity at the bottom are observed several kilometers away from the discharge point. Salinity increases reach to all the deep localities (20 m) and to most of the shallow (16 m) localities with the exception of the northern one. Results in the August survey (Fig. 5) are different since maximum salinity was not found at the bottom. At the bottom (Fig. 5b) salinity increase is observed only during the first hundreds of meters which may produce an incorrect feeling of dilution. At the termocline level, where maximum salinity is observed, the same pattern than in previous surveys was found (Fig. 5c).
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A Salinity
B
41.6 41.4 41.2 41 40.8 40.6 40.4 40.2 40 39.8 39.6 39.4 39.2 39 38.8 38.6 38.4 38.2 38 37.8 37.6 37.4 37.2
Salinity
B
C
Fig. 4. Spatial distribution of salinity on the surface (a) and on the bottom (b) during the campaign of April 2004.
Echinoderms have disappeared from the meadow in front of the desalination plant and Urbanova (southern locality) after the impact (Fig. 6). At the northern locality (Alicante Harbour) an important increment is observed in February followed by a decrease to lower values than before the operation of the desalination plant. These results are coherent with the dispersion of the brine since the northern locality is the less affected by the brine. Survey of Posidonia oceanica shows, at all the localities, that the number of new shoots
41.6 41.4 41.2 41 40.8 40.6 40.4 40.2 40 39.8 39.6 39.4 39.2 39 38.8 38.6 38.4 38.2 38 37.8 37.6 37.4 37.2
Fig. 5. Representation of the superficial (a), bottom (b) and the maximum salinities (c) obtained at August 2004.
produced between June 2003 and August 2004 is higher than the number of dead
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2004 W
16 m
20
2004 S
20 m
18
0.6 Shoot division rate (%)
Density of echinoderms (ind/m2)
0.7
0.5 0.4 0.3 0.2 0.1
16 14 12 10 8 6 4 2
0 Harbour
Urbanova
0
Desalination plant
Harbour
Urbanova 16 m 20 m
Desalination plant
Harbour
Urbanova 16 m 20 m
Desalination plant
Harbour
Urbanova
Desalination plant
5
shoots and, consequently, shoot balance is positive (Fig. 7). However, the higher vitality is observed at the northern locality and the lower vitality in the meadows in front of the desalination plant discharge. 4. Discussion The place for the brine disposal of the Alicante desalination plant was chosen because the area was seriously damaged due to the expansion of the Alicante Harbour and several seawages that have produced the regression of Posidonia oceanica meadows. Before the desalination plant starts to operate in September 2003, P. Oceanica meadows appeared at 16 m depth and about 2 km from the disposal point. Our results showed that dilution was lower that what has been foreseen. Near the discharge point dilution is very strong but a layer of water of high density expands over the bottom to a distance of several kilometers. This low dilution is observed also in August when, due to the low temperature of water below termocline, the brine moves in the middle of the water column. However this situation is more
Shoot mortality rate (%)
4.5 4 3.5 3 2.5 2 1.5 1 0.5 0 18 16 14 Shoot balance (%)
Fig. 6. Mean values (and standard errors) of the density of echinoderms (individuals per m2) in the station closest to the desalination plant discharge and the two controls (Urbanova Beach and Alicante Harbour) during Summer 2003, Winter 2004 and Summer 2004.
12 10 8 6 4 2 0
Fig. 7. Division and mortality rates of the Posidonia oceanica shoots in the station closest to the desalination plant discharge and the two controls (Urbanova Beach and Alicante Harbour).
positive for benthic organisms that are not affected by higher salinities. Echinoderms have been chosen because they are osmoconformers organisms, which are not able to regulate their osmotic pressure. Several studies have demonstrated that they are only able to tolerate a narrow range of salinities. The disappearance of the echinoderms in the area of the brine influence may
Y. Ferna´ndez-Torquemada et al. / Desalination 182 (2005) 395–402
be used as an indicator of changes in the marine communities produced by the brine disposal of desalination plant. The temporal increase of echinoderms in the northern locality may be related with their movement away from the brine. Posidonia oceanica meadows are important communities in the Mediterranean Sea from an economic and ecological point of view and are protected in the entire basin. They are very sensitive to human activities and their regression is common in many locations of the Mediterranean. Recently it has been demonstrated the low tolerance of this species to salinity increments [18,19]. Salinity increments measured at the meadow in front of the desalination plant discharge are close to the ones that have produced significant effects on their growth and survival. Preliminary results obtained show that, during the first year of monitoring, the desalination plant has not produced the regression of the meadow but it has affected the vitality of the plants. The higher vitality has been observed in the northern locality, which is the less affected by the brine but the more affected by other sources of pollution. Our results show that dilution of the brine from a RO desalination plant may be lower than the usually accepted and may affect important extensions of marine communities. In order to minimize the impact of desalination plants it is important to select a correct location of the plants and to maximize the dilution of its brine. This may be achieved using a previous dilution of the brine with seawater that has been proved useful in other plants [20,21]. Acknowledgements We thank Just Bayle Sempere who assisted in the winter campaign of 2004. We also would like to thank Marina of Alicante for
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use of equipment and facilities. This work was funded by UTE Desaladora de Alicante and Mancomunidad de Canales del Taibilla and by a FPI grant from the Generalitat Valenciana (FPI 01 A 002). References [1] A.J. Morton, I.K. Callister and N.M. Wade, Environmental impacts of seawater distillation and reverse osmosis processes. Desalination, 108 (1996) 1–10. [2] T. Ho¨pner and J. Windelberg, Elements of environmental impact studies on coastal desalination plants. Desalination 108 (1996) 11–18. [3] J.L. Pe´rez Talavera and J.J. Quesada Ruiz, Identification of the mixing processes in brine discharges carried out in Barranco del Toro Beach, south of Gran Canaria (Canary Islands). Desalination 139 (2001) 277–286. [4] P. Glueckstern and M. Priel, Optimized brackish water desalination plants with minimum impact on the environment. Desalination 108 (1996) 19–26. [5] D. Squire, J. Murrer, P. Holden and C. Fitzpatrick, Disposal of reverse osmosis membrane concentrate. Desalination 108 (1996) 143–147. [6] M. Ahmed, W.H. Shayya, D. Hoey, A. Mahendran, R. Morris and J. Al-Handaly, Use of evaporation ponds for brine disposal in desalination plants. Desalination 130 (2000) 155–168. [7] M. Ahmed, W.H. Shayya, D. Hoey and J. Al-Handaly, Brine disposal from reverse osmosis desalination plants in Oman and the United Arab Emirates. Desalination 133 (2001) 135–147. [8] M. Ahmed, A. Arakel, D. Hoey, M.R. Thumarukudy, M.F.A. Goosen, M. Al-Haddabi and A. Al-Belushi, Feasibility of salt production from inland RO desalination plant reject brine: a case study. Desalination 158 (2003) 109–117. [9] S. Lattemann and T. Ho¨pner, Seawater desalination. Impacts of Brine and Chemical Discharges on the Marine Environment, Desalination Publications, L’Aquila, Italy, 2003. [10] J.V. Del Bene, G. Jirka and J. Largier, Ocean brine disposal. Desalination 97 (1994) 365–372. [11] E. Gacia and E. Ballesteros, El impacto de las plantas desalinizadoras sobre el medio marino:
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