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As on land, plants are the real producers in the sea, and on them depend all marine living resources and the basic sustainability of ecosystems. Primary production is performed by chlorophyll-bearing plants ranging from the tiny phytoplankton to the giant kelps through the process ofphotosynthesis. Zooplankton play an important role as secondary producers, and together with phytoplankton they support the vast assemblages of marine food chain with all their diversity and complexity. Data on chlorophyll pigments, phytoplankton and zooplankton are regarded as a sound basis for environmental appraisal of ecosystems. This paper presents a set of data collected from the Saudi Arabian coastal waters near the desalination plants in AI-Jubail. Materials were collected from six different sites covering the intake and discharge zones during cruises carried out in 1997–1998. Analyses of chlorophyll pigments were made using the spectrophotometric method. Plankton samples were collected using a Nansen plankton net with a mesh size of 75 μ and analyzed following standard procedures. Chlorophyll a, b, c and phaeophytin are the most commonly occurring pigments in seawater. Their concentrations showed wide fluctuation. The phytoplankton community was composed of 35 genera representing the Diatoms, Dinoflagellates and blue- green algae. Zooplankton were composed ofProtozoa, Coelenterata, Ctenophora, Aschelminthes, Annelida, Mollusca, Arthropoda, Echinodermata and Chordata. Arthropoda, represented by Cladocera, Copepoda and Crustacean larvae, formed the largest group followed by Chordata. The distribution of phyto- and zooplankton was examined and discussed on a seasonal, annual and inter-annual basis. In terms of species, overall species composition was not affected by plant discharge. The study brings out a greater understanding of the changes experienced by biotic communities as a result of impingement, entrainment and entrapment consequent to water passage through the plant structures. The study reflects the ecological relationships that the phytoplankton and the zooplankton of the region possess with respect to intake and discharge. Further, the study has brought to light a very redeeming feature of the ecosystem to sustain its productivity and planktonic abundance. It was observed that seawater temperature, conductivity and total suspended solids did not act as limiting factors. Besides throwing much light on the little known biological aspects of desalination sites, the data provided constitute a significant addition to the knowledge base of marine living resources in an industrial zone of Gulf coastal waters.

The problem of macrofouling has serious implications in the performance of desalination and power plants. Intake structures, screens, seawater piping systems and heat-exchanger tubes are the sites worst affected in the plants, causing an overall decline in plant efficiency at great economic cost. The last half century has witnessed significant advancements in the development ofmacrofouling control technologies. Materials of inherent antifouling properties are widely used in the construction sector. Control technologies available include antifouling paints and coatings, injection of biocides, marine bio-active compounds, materials of inherent antifouling properties, heat treatment, pulse-power devices, UV and nuclear radiation, scrubbing devices, biological control, etc. A literature search carried out during the last few years has yielded about 450 references. This paper presents, in a very concise manner, state-of-the- art macrofouling control technologies pertinent to desalination and power plants in the Kingdom. The paper also discusses the issues of biofouling control in the Al-Jubail plants based on the results of an on-line macrofouling experiment conducted in one of the turbine condensers of Al-Jubail phase-I MSF/power plants.

Earlier work at Saline Water Conversion Corporation (SWCC) R&D Center showed that nanofiltration (NF) pretreatment of seawater feed to seawater desalination plants removed from its turbidity and microorganism, caused significant rejection of the scale forming hardness ions, reduced TDS in Gulf seawater and produced a new, partially desalinated seawater product, considerably different and superior to seawater in qualities and without the problems normally associated with seawater of high concentration of scale forming ions, high TDS, high turbidity and high bacteria count. Integration of the NF unit with one of the conventional desalination processes to form for example an NF-SWRO lead to a significant improvement in the seawater desalination processes, for example by doubling the SWRO product water output and recovery ratio and the production of high purity permeate (TDS

A study was carried out in the sea adjacent to a major MSF plant where a new 24MGD SWRO plant is being commissioned. Data were collected on the topographical feature of the marine basin, water quality and plankton of the intake zone. The incidents of planktonic bloom, influx of invasive organisms like jellyfish and macrofouling organisms and ingress of marine algae were monitored regularly. The Intake Bay of the plant is a well designed man-made structure studded to the coast. The marine basin in Al-Jubail, is for geological reasons, a shallow gently sloping shelf while the bay proper is a dredged, deeper basin. The area outside the bay is a vast sea grass bed and the seafloor sediment is sandy. The drag of seawater maintained by the intake pumps facilitates the transport of sediment particles, uprooted algae and floating objects creating fouling problems inside the plant. Seawater temperatures, conductivity, pH, dissolved oxygen and trace metals were found to be very much benign to the trouble free operation of the plant. Influx of jellyfish, noticed during the summer, was not found to be very severe. Data on plankton showed the presence of many phyto and zooplankton organism of biofouling potential in the plant. Total suspended solids indicated the possibility of the intake bay becoming a source of elevated Silt Density Index (SDI) for the new SWRO plant. The paper considers the data in detail and discusses the effects of environment on the desalination plant in Al-Jubail and suggests certain strategies for the protection of seawater intakes and some points useful in the siting and design of coastal seawater intakes in the region.

Salt carry-over due to excessive foaming in a multistage flash (MSF) distiller and detrimental foaming in the deaerator section have been reported in the Saline Water Conversion Corporation (SWCC) of Saudi Arabia and other desalination plants. The application of a suitable antifoaming agent has prevented distillate contamination and improved release of dissolved oxygen in the deaerator section, thus improving the operating efficiency of MSF plants. The developer of a polyoxypropylene glycol-based antifoaming agent collaborated with SWCC in carrying out trial runs to show that their product was as effective and economical as the one currently being used (a polyglycol blend in a hydrocarbon solvent) in SWCC plants. Trial tests were carried out at laboratory, pilot and commercial plant levels. Miscibility of this agent in water was determined initially in the laboratory, followed by field trial runs in an MSF pilot plant and the commercial plants of Al-Jubail I and II. Foam control, non-interference with antiscalant performance, distillate purity and stability at a low dose rate over a wide range of temperatures were some of the important criteria evaluated during testing of this antifoaming agent. During MSF plant runs, distillate conductivity and dissolved oxygen level in the feed were regularly monitored and found within the acceptable limits. Compatibility of this agent with antiscalant was also assessed. Heat transfer and plant performance data were found satisfactory confirming that this agent did not exhibit any adverse effect on the antiscalant used in Al-Jubail plants. Results of laboratory and field trial runs of this antifoaming agent are discussed.

In this new approach to membrane and thermal seawater desalination processes developed by the Saline Water Conversion Corporation (SWCC), R&D Center, a nanofiltration (NF) membrane unit, which received non-coagulated filtered seawater feed, was placed ahead of the SWRO and the MSF pilot plant units to form, for the first time ever, fully integrated desalination systems of an NF-SWRO, NF-MSF, and NF-SWROreject-MSF. Preliminary results were presented at the IDA World Congress, Madrid '97. Further results obtained in this investigation at a pressure of 22 bars showed that the NF unit reduced turbidity and microorganisms, removed hardness ions of Ca++, Mg++, SO4=, HCO3−, and total hardness by 89.6%, 94.0%, 97.8%, 76.6% and 93.3%, respectively. The system also resulted in the reduction of the monovalent ions of Cl−, Na+, K+ each by 40.3% and the overall seawater TDS by 57.7%. The seawater (NF permeate water) produced by this process is considerably different in composition from (Gulf) seawater, and quality-wise is far superior to it as a feed to seawater desalination plants, and moreover without the problems normally associated with high concentration in seawater of scale forming ions, high TDS, high turbidity and microorganisms. This made it possible to operate both the SWRO and MSF pilot plants at high water recovery: 70% and 80%, respectively. It also allowed for the successful operation of the MSF unit at top brine temperature of 120°C without the addition to the make-up of antiscalant or acid or antifoam. The said desalination arrangements lead to significant improvement in the seawater desalination processes by lowering their energy consumption, by about 25–30%, and reducing chemical consumption thereby making the process more friendly to the marine environment. The observed increases in their product water output and recovery ratio by more than 70% resulted in the ultimate benefit of lowering the estimated cost of fresh water production by more than 27%. The SWRO permeate produced from the NF-SWRO arrangement has very low TDS, ≤200 ppm, making the requirement for a second-stage RO treatment of the SWRO permeate unnecessary. Moreover, the use of the desalination arrangement NF-SWROreject-MSF should allow for the conversion of up to 90% of the NF product into fresh water, where about 65% of the NF product is converted to fresh water by the SWRO unit and 25% of SWRO reject is converted by the MSF unit. Definitely, the achievement of the above results represents a milestone in seawater desalination technology. The paper describes the results obtained, the experimental approach used in this investigation along with description of the NF-SWRO, NF-MSF and NF-SWROreject-MSF pilot plants employed in this study. A simulated desalination model which compares the operation of existing SWRO plants with and without the NF modification is also described along with the technoeconomics of process analysis.