Environmental Impact of Brine Disposal

Environmental impact of brine disposalon Posidonia seagrasses

Manuel Latorre

ACSEGURA, S.A., C/Fuensanta, 4 1�B, 30001 Murcia, Spain Tel. +34 96 8355346; Fax +34 96 8222325;email: [email protected]

Received 21 January 2005; accepted 21 February 2005

Abstract

The location of big SWRO plants is usually limited by environmental restrictions such as the presence of the

Posidonia habitat in the Mediterranean coast. The unknown impacts of brine on the flora and fauna associated

at sea grasses has caused environmental damages either high cost disposal solutions of doubtful viability.

Previous to the construction of 160.000 m3/day SWRO Plant in the southeast coast of Spain, an unique research

study was carried out in the Mediterranean coast by some of the most advanced Spanish Research Centres in

cooperation with two Spanish universities. The knowledge of the Posidonia limits can help not only to locate

Desalination plants but to design disposal devices. This paper reports the results of two years study testing the

salinity impact on Posidonia habitat lab and field with brine produced with a SWRO pilot plant. Additionally a

brine disposal model has been developed to support the design of a full scale disposal system.

Keywords: brine, Posidonia, desalination impact, high salinity discharge

1. Introduction

In December 1999, the public companyAcsegura received the order from the SpanishGovernment to build and operate a SeaWater Desalination Plant of 140,000 m3/daylocated in the southeast of Spain in MurciaRegion. The Mediterranean coast of Spain iscovered by the sea grasses of Posidonia ocea-nica, included in the list of protected habitatsof the EC.

The ‘‘Habitats’’ Directive 92/43/EEC [1] isa Community legislative instrument in the field

of nature conservation that establishes acommon framework for the conservation ofwild animal and plant species and natural habi-tats of community importance; it provides forthe creation of a network of special areas ofconservation, called Natura 2000, to ‘‘maintainand restore, at favourable conservation status,natural habitats and species of wild fauna andflora of Community interest’’. Habitat 1120 *Posidonia beds (Posidonion oceanicae) include:

1. Beds of P. oceanica (Linnaeus) Delilecharacteristic of the infralittoral zone of the

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 � 2005 Elsevier B.V. All rights reserveddoi:10.1016/j.desal.2005.02.039

Desalination 182 (2005) 517–524

Mediterranean (depth: ranging from a few dozencentimetres to 30–40 m). On hard or soft sub-strate, these beds constitute one of the mainclimax communities. They can withstand rela-tively large variations in temperature and watermovement, but are sensitive to desalination,generally requiring a salinity of between 36and 39%.

2. Plants: P. oceanica.Animals: Molluscs, Pinna nobilis; Echino-

derms, Asterina pancerii, Paracentrotus livi-dus; Fish, Epinephelus guaza, Hippocampusramulosus.

P. oceanica is widely extended around theMediterranean sea ranging from a few dozencentimetres to 30–40 m. P. oceanica is an ende-mic plant in theMediterranean with roots, stalk,leaves and fruits that lives under water betweenthe surface and a maximum depth of 40 m. Theplant forms beds of Posidonia that are the mostimportant ecosystem of the Mediterranean,equivalent to the forests of the land ecosystems.Posidonia situated on the sandy seabed andrarely on rocky beds that supply great quantitiesof oxygen and organic material contributing,also, to the balance of sediment on formingbarrier reefs that maintain the coastal stabilityand protect the beaches from erosion.

The fields of Posidonia are also a greatsource of biodiversity as they are the habitatof numerous vegetable and animal species,some of which are in danger of extinction.The P. oceanica has an annual growth cycleand the dead leaves, sometimes in the form ofballs, are deposited on the beaches, protectingthem from the erosion caused by the waves.

In spite the P. oceanica great importance,the regression is becoming usual due tohuman activities, such as fishery, aquiculture,effluents discharges, beaches regeneration,marinas, etc. producing a direct or indirectimpact on the Posidonia or the environment.

Posidonia oceanicaL.Del., aMediterraneanendemic species, is one of the best-known as

well as the most endangered plants in the Med-iterranean Sea [4]. It is not an alga but a flower-ing plant, i.e. a vascular plant with all thecharacteristic woody parts—rhizome androots, leaves, flowers and fruits. At first sightit reminds us of grasses; this is the reason whywe usually refer to it as to a grass, which can bealso said of other flowering plants living in oursea—Cymodocea nodosa, Zostera marina andZostera nana.

Its name—named after Poseidon, the chiefgod of the sea—seems very appropriateindeed, for its extensive underwater meadowsthat spread from the shore to the depth of40 m representing one of the key ecosystemsof the Mediterranean Sea. Most often theyare found on sandy floors, less often onhard ground. Its rhizomes, which can growhorizontally or vertically, are densely inter-twined and constitute a kind of a secondaryBottom. They may be several decimetresthick and can create actual reefs at someplaces. At the tip of each rhizome there is ashoot of a centimetre wide and even morethan a metre long leaves. Their numbersvary during the year, ranging between 5 and8. The older leaves situated on the outer sideof the shoot fall off but are soon replaced bynew ones growing in the shoot’s interior.

The meadows of P. oceanica are of greatimportance for the marine ecosystem, not onlyin view of producing oxygen and organic sub-stances (approximately 20 tons/ha/year) butalso as a biotope for an infinite number ofmarine organisms dependent on such meadowsin terms of their diet, habitat, shelter, etc. Thereare also many sessile organisms, which liveattached to the surface of the leaves and rhi-zomes. There is of course more than enoughplaces for them, considering that the actual sur-face area of all leaves in a single square metre ofa meadow ranges from 20 to 50 m2. Posidoniameadows are at the same time a very importantfactor in the diminishing of erosion. In spite of

518 M. Latorre / Desalination 182 (2005) 517–524

these entire positive characteristics, less and lessnatural habitats of this plant have beenobserved in the Mediterranean particularlydue to various construction works, pollution,drag netting, anchoring, etc.

P. oceanica has been declared endangeredin many areas of Mediterranean. In this mea-dow numerous marine organisms have beennoted, most perceivable amongst them beingPina nobiliss, various sponges, crabs (Maiaverrucosa, Pagurus sp.), gastropods (Murexsp.) and bivalve molluscs (Chlamis varius,Aca noe). The habitat represents an ecosystemthat plays an important part in the exchangeof substances in the sea and, which is ofparticular significance, provides a biotope,hiding place and a refuge for numerous mar-ine organisms and thus contributes towardsthe diversity of the underwater world aswellas the conservation of ecological process [2].

Biological cycle is similar to a land plant.Flowers appear between September and Octo-ber and fruits around spring time. Plant grow-ing is continuous through the year highlyaffected by the lighting and temperature ofthe water. Mayor growing occurs duringspring and summer, being minimized at winterseason.

2. Impacts on Posidonia meadows

Posidonia beds are not rare (France alonehas 1,15,000 ha) they have suffered a progres-sive and irreversible regression throughoutthe Mediterranean due to:� Sand extraction and development of infra-

structure, harbours and artificial beaches,enhancing turbidity and covering the bedswith sand.

� Damming of rivers. Changes in sedimen-tation in the littoral zone have led toeither exposing or burying of habitat.

� Trawling and anchoring are especiallydestructive to exposed rhizomes [7].

� Eutrophyication, augmenting algal blooming.Sewage and industrial waste discharge cause acomplete loss of the habitat locally.Caulerpa taxifolia (an tropical alga intro-

duced in the French Mediterranean in 1984) isprogressively overwhelming Posidonia beds.

According Marba, N (1996) 78% of thePosidonia sea grass along Mediterraneancoast of Spain is affected by density decreas-ing. The situation in the Westersn Mediter-ranean is most serious. Shoot density israpidly decreasing, up to 50% over a fewdecades. Besides, increased turbidity andpollution have resulted into a squeeze ofthe beds; in various places living beds havewithdrawn between 10 and 20 m depth.Dead beds occur abundantly, even in waterswhich have already been protected for 35years. For the French mainland coast habi-tat loss is estimated 10–15%; but taking intoaccount the decrease of shoot density theoverall decline of the resource will bebetween 30 and 40%. This is probably agood estimate for most western Mediterra-nean coastlines, although the situationaround the islands and in the eastern Medi-terranean is better.

The main ecological requirement of Posido-nia, as plant consists of a good illumination,what determines it doesn’t exists below a cer-tain depth, at which the light necessary doesnot arrive to maintain its requirements. Agood part of the negative effects originatedby the human activities takes place, indeed,increasing the turbidity of waters preventingor making difficult the penetration of the light.

It is known, in addition, that in estuarialatmospheres or mouths of rivers they arehabitats on which these communities are notbased, what means that a low salinity is nottolerated by the Posidonia.

Considering the ecological characteristicsof P. oceanica, very demanding in the envir-onmental conditions, and analyzing its areas

519M. Latorre / Desalination 182 (2005) 517–524

of distribution can be reached the conclusion,that it does not support an ample rank ofvariation in the salinity of waters.

However, before approaching the worksobject of the present paper, it was not knownnor existed documentary references on the tol-erance(not even approximated) that can havethe plant to the increases of salinity reason whythe accomplishment was indispensable fromthe different studies that, through differentapproaches, they could approach us the knowl-edge of the effects that the increase of salinitypresents on Posidonia, in the way to try todefine certain ranks of salinity for which theeffects are critical, serious, moderate or slightand, based on which to be able to determinethe proportions of suitable way out the spills tothe water sea from desalination plants.

Is evident that a solution, considered uptoday consists of locating the spill in a zoneno colonized by meadows, but this is notalways possible in certain zones of our geo-graphy and, more in particular, within theRegion of Murcia in which in a high percen-tage, its coast is fortunately occupied by theseimportant vegetal colonies [3].

One second solution would consist oflocating the device of spill to a greater depththan the occupied one by the meadows, beingbased on the criterion of which the hypersaltywater, as being denser than the one of the sea,it will tend to move at any moment towardsdeeper zones. This alternative presents, in ouropinion, three disadvantages:� Its high economic cost, when needing a con-

duction of great length, equal like minimumto the width of the prairie (several kilo-metres in certain zones of theMediterraneancoast).

� The necessity to excavate a ditch or toinstall an important number of anchoragesfor such emissary throughout the wide oneof the prairie, what will have a doubtlessphysical effect that, in the case of a ditch it

can extend on a quite greater surface toboth sides of the same one.

� Spill can not affect to prairie of Posidonia butif it would have negative effects on other com-munities that colonize the bottoms of greaterdepths, as it could be, for example, maerl.The knowledge of the tolerance ofP. oceanica

to the increases of salinity can, combined withmeasures that increase the dilution of the efflu-ents, cause that the accomplishment canbe envir-onmentally permissible fromabrine spill on or inthe environs of a zone colonized by these prairies.

3. Investigation approach

In order to minimize the impact of the brinedischarge of the SWRO plant on the Posidoniabeds, ACSEGURA asked CEDEX to study theeffect of the high salinity on the plants, as therewas no knowledge at all about it. Therefore theinvestigation further presented is the first timein the world is carried out linking desalinationwith impact on Posidonia seagrass.

This investigation focused on the design ofthe discharge method of the SWRO Plant tominimize the environmental impact of thehigh salinity brine discharge on the marinehabitats and design the disposal method toachieve that goal.

The first stage of any investigation is theresearch of any bibliography related with thegoal or subjects included in. In this case refer-ences related with the investigation were verylimited and there were no previous investiga-tions about the effect of high salinitydischarge on Posidonia beds. Existing docu-ments are related to the effects of low salinity,coming from sewage disposal instead of highsalinity effects.

Therefore, the path of the investigationwas entirely new and the analysis proposalshad to be set from the origin. The lack ofknowledge in this field set the opportunity toface up a great challenge.


An additional difficulty to set the researchwas to know if it was possible to adapt Posi-donia bundles into laboratory conditions inaquariums, as this was the first level initiallyplanned for the research. Laboratory researchis always the first approximation to anyinvestigation involving flora and fauna, pre-vious to study field conditions. Any labora-tory research has the advantage thepossibility to keep under control the test con-ditions as temperature, light and salinity.Additionally tests can be replicated and setreference parameters limiting the uncertaintyof the results.

Field tests have as main advantage thatnatural conditions are not affected; however,the replica possibilities and conditions of thetests are not always possible. In any case thecombination of both, laboratory and fieldgave as the possibility to contrast the preli-minary results obtained at laboratory in thefinal tests carried out on the field.

Methodology used in the investigation wasplanned according different levels of approx-imation in order to evaluate the response ofPosidonia to the experimental conditionssimilar to a high salinity discharge. So threedifferent levels were analyzed:

1. Mesocosmos experiments (lab)2. Macrocosms level (field)3. Validation of obtained results compar-

ing with the effects of brine coming fromworking desalination plants.(field)

As it was mentioned previously, the lackof knowledge and preliminary investigationsin this field, mean a great challenge requiringscientific contributions from the most quali-fied national experts. Some institutions anduniversities gather the information onnational and regional particularities, as wellas types of associated habitats. The finalreport was compiled by the CEDEX, basedon the contributions of the following groupsof experts:

� Instituto Espanol de Oceanografıa. CentroOceanografico de Murcia (IEO).

� Consejo Superior de Investigaciones Cien-tıficas. Centro de Estudios Avanzados deBlanes (CEAB).

� Universidad de Barcelona. Departamentode Ecologıa (UB).

� Universidad de Alicante. Departamentode Ciencias Ambientales y Recursos Nat-urales (UA).University of Alicante was in charge of lab

research and the field investigations were car-ried out by the IEO, CEAB and UB.

The final report and conclusions wasapproved by agreement of all the participantsin March 2003.

4. Experimental proceedings

Each one of the approach levels that finishbeing mentioned integrate a series of tests andanalyses that are the following ones:

4.1. Answer to the salinity in mesocosmos

Experiments with P oceanica were made intanks of medium volume, in the short term(15 days) and the main descriptors studiedwere the survival and the growth in plants.In each test the environmental factors in eachone of the aquariums were controlled (light,salinity and temperature) that stayed mostconstant than it was possible.

Likewise some tests were made with twospecies of fauna associated to the Posidoniasea grass: misidaceum and sea urchims.

4.2. Study of the effects of spills from existingdesalination plants on P. oceanica (studies inthe field)

A good approach to the knowledge of theenvironmental effects of a certain humanactivity is the observation of previous perfor-mances the most seemed possible to which is


tried to evaluate. In the case that occupies tous, desalination plants in the coast have beingin operation for several years, reason why inprinciple the accomplishment of recognitionsof field around some of the selected spillsseemed possible.

The main disadvantage of this level ofapproach resides in the interpretation of theresults since the well observed effects also canbe originated by the increase of salinity origi-nated by the brine spill but also by otherfactors, such as the increase of turbidity gen-erated in sweeps, the chemical agent addition,etc.; or it even could be that the meadowsalready presented a certain state of degrada-tion originated by causes having nothing incommon to the spill. Therefore, for the suita-ble interpretation of the results of this part ofthe investigation it will be needed, necessarily,of the support of the other two integratedlevels of approach in the investigation.

After a search between the Spanish plantsin operation and after diverse works of recog-nition in the desalination plant of Camp deMar, in Andraitx (Mallorca), finally this partof the study was focus on the desalinationplant of Formentera, where it was made anintense recognition and an important numberof salinity measures.

4.3. Simulation of the saline spill on beds ofP. oceanica (macrocosmos)

This third level of approach was designedinitially along with the previous ones, neverthe-less its greater complexity caused that it beganwhen the other twowere in an advanced state ofaccomplishment, with which the accumulatedexperience was used for the suitable design ofthese experiences.

The work considered by means of thepursuit of the effects of small hypersalinespills on the micro scale distribution of Posi-donia. From the spill of a plant pilot,

constructed by ACSEGURA in San Pedrodel Pinatar, after the dilution adapted to thesalinities to try, one canalized small spillstowards experimental parcels, previouslycharacterized.

Considering that, due to the experimentalcomplexity, two salinities could solely betried, at sight of the results of the other levelsof the investigation, it was decided on a highsalinity, that it turned out to be of 38.4 psuand other salinity that we will denominatevery high, of 39.2 psu.

5. Results

The different made experimentalapproaches offer a vision, also differentfrom the effects that the increase of salinityoriginates on Posidonia. Thus, whereasthe laboratory tests offer a valuable infor-mation of the short term effects, the testsof mesocosmos and, mainly, the recogni-tions of field, they approach to us muchmore the chronic effects at medium andlong term. So, it is no rare that some effectsobserved in the laboratory experiments tobe increased in the remaining levels ofapproach.

Preliminary results pointed out byCEDEX were as follows [8]:

1. Has been verified, without doubt, thatfanerogamme marine P. oceanica is little toler-ant to the increase of salinity, originating dif-ferent negative effects when the salinity isincreased above its habitual values (increaseof mortality, appearance of necrosis in weavesand greater fall of leaves).

2. In agreement with the experimentsmade in laboratory, salinities in the surround-ings of 50 psu originate the death of the100% of the plants in 15 days.

3. Mortalities of the order of 50% of theplants are reached with salinities around45 psu.


4. A salinity of 40 psu originates a mortal-ity of 27% of the plants, although experimentsmade with superior salinities gave discordantresults (20% of mortality for 43 psu asopposed to 55% of mortality for 42.9 psu).5. In the laboratory experiments it was fre-

quent to observe a mortality of a certainpercentage of plants in the treatments withwater at salinity of the sea, that as averageit turned out to be from 8.5% (varyingbetween 0 and 15%).6. Regarding the growth of the plants, the

experiments showed that over 48–50 psu theplants let grow completely.7. The rates of growth are reduced on the

growth to salinity of 38 psu in the followingaverage rates:�With salinity around 43 psuPosidonia growth isthe half of the growth at natural sea salinity.� With salinity around 40–41 psu the plantsgrowth is an average a 14% less than withnatural salinity of the sea.8. If the increase of salinity has not been

excessive, returning into the conditions ofnormal salinity, the rate of growth returnsto its normal values in high percentage,being reached a total recovery of the beamsgiven a treatment of 43 psu.9. The data which it has come to indicate

that to cause the effects of mortality anddiminution of the rate of growth it is notnecessary that the totality of the plant thissubmerged in the hypersalty water but thatis enough whereupon the basal part of thesame one is it.10. Of the recognitions of field it is possible

to emphasize that it has been verified that,independently of the effects that could origi-nate on the prairie the increase of salinity, theeffluent of the plant of Formentera at leastoriginates an increase in nutrients in thewater which can be origin of some of theeffects of degradation of the meadows whichthey have been possible to observe.

11. The prairie next to the emissary, in anadvanced state of degradation one was bathedby waters of salinity between 39 and 43.4 psu,although the evidence does not exist, accord-ing to the equipment of CEAB and UB, ofwhich the degradation has been originated bythe increase of salinity.12. The discontinuous meadows, with affec-

tion of the density and cover, one was bathedby waters between 38.6 and 40 psu.13. Finally, the continuous meadows, in

that the affection due to the increase ofsalinity is let notice at behaviour level andcharacteristics of the plants but that it doesnot seem to affect the density and coverof the prairie was, at the moment of themeasures, affected by salinities between38 and 39.5 psu.

6. Conclusions

Once known the results corresponding tothe tests made by the experimental IEO withwater spills on experimental parcels, like com-plementary works that have come developingon the part of the rest from the participantgroups, the final conclusions of the study ofthe CEDEX, in which to tolerance to theincrease of salinity of Posidonia, they werethe following ones:1. A criterion of sizing relative to the tol-

erance of Posidonia has settled down basedon the obtained results of the different experi-mental approaches made and having inaccount the principle of precaution, whatmeans all the values, adopted as a conse-quence of the present research must notbeen definitive results and can be modifiedin the future according investigationsadvances.2. Based on the previous assumption, the

recommendations of the investigation were:� Brine discharge from desalination SWRO

plants must be avoided on P. oceanica


meadows, being preferred to discharge onsandy bottoms without flora.

� If previous recommendation is not possi-ble, the discharge must be such that neverhappen 25% of the time above 38.5 psuneither 5% of the time above 40 psu.3. The previous values correspond to a dilu-

tion of the water so that, in agreement with theobtained results, the Posidonia would notundergo significant deterioration some due tothe increase of salinity. However, it correspondsto the competent Environmental Authority ineach case to authorize the spill to adopt thevalue that considers more advisable at sight ofthe results of the different studies.4. Some results indicate that salinity toler-

ance of Posidonia locate at low depth andtherefore with high level of lighting, is higherthan the plants locate at deeper position, whatsuggest than depth is also a factor to be con-sidered at disposal authorization time.5. In the case of the SWRO Plant located at

Mazarron Bay the discharge of the brine is dis-charged through a 1600 mm HDPE pipeequipped with 20 fittings of diameter between120 and 180 mm 1 m above the pipe. The dis-charge angle is 60� above the horizontal.

References

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