Impact of desalination plants fluid effluents on the integrity of seawater, with the Arabian Gulf in perspective

Abstract

As generally seen benign, seawater desalination is not without environmental concerns of its own. All over the world, in thermal desalination plants, seawater feed is heated to extreme temperatures, mixed with chemicals and desalted to produce fresh desalinated water, together with by-product of concentrated brine-solutions that become released back into the sea. Today, all around the world, and in the Arabian Gulf Region in particular, much of the fresh water needs are being obtained from seawater through the various processes of desalination, which mainly include heatbased processes (e.g. Multi-Stage Flash (MSF), Multiple Effect Distillation (MED) and Vapour Compression (VC)) and membrane processes (Seawater Reverse Osmosis (SWRO)). Concentrated brines from MSF plants (with TDS exceeding that of the seawater-feed, elevated temperatures and containing chemical-residuals) are, regrettably, discharged into the oceans and seas without any treatment, with an overwhelming world-wide conscious-disregard to the potential of hidden dangers and virulent effects on global marine eco-systems, while the effluent temperature plays a vital role in this orchestration. In the Arabian Gulf alone, MSF desalination plants treat huge volumes of seawater (in excess of 25 million m 3/day) so to obtain desalinated water of ≈5–10 million m 3/d (forgetting-not the other heat-based processes, such as MED, that are increasingly emerging into use today). The remainder (in the neighbourhood of about 20 million m 3/day of very heated and concentrated brine) is returned back to the sea, an issue that has today become of growing controversial concerns. The product water recovery for most heat-based seawater desalination plants is between 15 and 50% (and that for membrane-based processes is between 30 and 40%), produced along with brine containing concentrated solution of all the dissolved solids that were originally present in the seawater-feed. On the other hand, the lesser saline brine (retentate) from SWRO desalination plants, where there is no heat involved (with less chemical (eynord) residuals), may have a relatively minor adversity on marine ecology. Regrettably, there exists NO strict and binding legislation on the quality control of fluid-effluents from desalination plants into the sea and NO treatments what-so-ever for these effluents. The vigilant observant may mistakenly-comprehend that desalinated water is indispensably required at any cost, regardless of the side-effect impacts of these effluents on marine environment and on seawater integrity, and the disturbances that this causes onto the ecological systems in the oceans and seas. This paper shall take a glance at the fluid effluents analysis-data from two MSF plants and two RO plants around the Arabian Gulf compared-against the Standard of Industrial Effluents limits for the Kingdom of Bahrain, to envision where-we-stand and where-we-should-be, and attempt to highlight the invisible dangers of desalination fluid-effluents. It would be also appropriate to articulate a digest with global vision on the availability of fresh water from oceans and seas and to illustrate an insightful-overview of seawater RO desalination history with global-insight touching on a few crucial water issues.