Environmental impact of brine disposal on Posidonia seagrasses

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.

Once known the results corresponding to the tests made by the experimental IEO with water spills on experimental parcels, like complementary works that have come developing on the part of the rest from the participant groups, the final conclusions of the study of the CEDEX, in which to tolerance to the increase of salinity of Posidonia, they were the following ones: 1. A criterion of sizing relative to the tolerance of Posidonia has settled down based on the obtained results of the different experimental approaches made and having in account the principle of precaution, what means all the values, adopted as a consequence of the present research must not been definitive results and can be modified in the future according investigations advances. 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 on sandy bottoms without flora.  If previous recommendation is not possible, the discharge must be such that never happen 25% of the time above 38.5 psu neither 5% of the time above 40 psu. 3. The previous values correspond to a dilution of the water so that, in agreement with the obtained results, the Posidonia would not undergo significant deterioration some due to the increase of salinity. However, it corresponds to the competent Environmental Authority in each case to authorize the spill to adopt the value that considers more advisable at sight of the results of the different studies. 4. Some results indicate that salinity tolerance of Posidonia locate at low depth and therefore with high level of lighting, is higher than the plants locate at deeper position, what suggest than depth is also a factor to be considered at disposal authorization time. 5. In the case of the SWRO Plant located at ´ Mazarron Bay the discharge of the brine is discharged through a 1600 mm HDPE pipe equipped with 20 fittings of diameter between 120 and 180 mm 1 m above the pipe. The discharge angle is 60 above the horizontal.