Ce travail a été réalisé dans le cadre d’une étude lancée par la compagnie HUTA sur ses installations de dessalement d’eau de mer. Le procédé de dessalement des eaux de mer le plus utilisé pour la production d’eau douce est l’osmose inverse (SWRO). Une station type, installée dans d’une zone industrielle, a été choisie pour mener cette étude d’optimisation du fonctionnement pour réduire les coûts d’exploitation. L’impact des rejets des rejets sur le milieu naturel a été également étudié. La station de dessalement sélectionnée pour les travaux de recherches est située dans la région Ouest de l’Arabie Saoudite à 160 km au nord de Djeddah, dans une zone industrielle pétrochimique (Raffinerie PETRO RABIGH), site ultra sécurisée, les captages des eaux de mer se font dans la zone côtière proche du site en Mer Rouge.L’étude se concentre principalement sur 3 parties : La première concerne la prise d’eau "INTAKE", différent mode captage ont été testé avec l’installation d’un ouvrage développé spécifiquement pour la station de Rabigh en s’adaptant aux règles imposées par les autorités Saoudienne. La deuxième est réservée aux procédés membranaires et l’importance des prétraitements dans la filière de désalinisation. La dernière partie concerne l’étude d’impact environnemental des rejets industriels "OUTLET" sur le milieu récepteur. / This study was carried in some seawater desalination plants of HUTA Company. The most used seawater desalination process for freshwater production is Reverse Osmosis (SWRO). A typical station, installed in an industrial zone, was selected to conduct this optimization study in order to reduce operating costs. The desalination station selected for this research work is located in the western region of Kingdom Saudi Arabia (KSA), at 160 km north of Jeddah city, in a petrochemical industrial zone (PETRO RABIGH Refinery), an ultra security site, seawater catchments occur in the coastal zone close to the site in the Red Sea.The study focuses mainly on 3 parts, the first one concerns the water intake "INTAKE", different intake mode were tested with the installation of a prototype structure developed specifically for Rabigh station in order to respect the Saudi authorities regulation. The second part is reserved to the membrane processes and the importance of pretreatments in desalination process. The last part focuses on the environmental impact of industrial waste "OUTLET" on the aquatic system. Finally the best decision and the best operation conditions have been concluded.

Increasing demand for fresh water in arid and semi-arid areas, similar to the Middle East, pushed for the use of seawater desalination techniques to augment freshwater. Seawater Reverse Osmosis (SWRO) is one of the techniques that have been commonly used due to its cost effectiveness. Recently, the use of Ultrafiltration (UF) was recommended as an effective pretreatment for SWRO membranes, as opposed to conventional methods (i.e. sand filtration). During UF operation, intermittent cleaning is required to remove particles and contaminants from the membrane's surface and pores. The different cleaning steps consume chemicals and portion of the product water, resulting in a decrease in the overall effectiveness of the process and hence an increase in the production cost. This research focused on increasing the plant's efficiency through optimizing the cleaning protocol without jeopardizing the effectiveness of the cleaning process. For that purpose, the design of experiment (DOE) focused on testing different combinations of these cleaning steps while all other parameters (such as filtration flux or backwash flux) remained constant. The only chemical used was NaOCI during the end of each experiment to restore the trans-membrane pressure (TMP) to its original state. Two trains of Dow™ Ultrafiltration SFP-2880 were run in parallel for this study. The first train (named UF1) was kept at the manufacturer's recommended cleaning steps and frequencies, while the second train (named UF2) was varied according to the DOE. The normalized final TMP was compared to the normalized initial TMP to measure the fouling rate of the membrane at the end of each experiment. The research was supported by laboratory analysis to investigate the cause of the error in the data by analyzing water samples collected at different locations. Visual inspection on the results from the control unit showed that the data cannot be reproduced with the current feed water quality. Statistical analysis using SAS JMP® was performed on the data obtained from UF2 determined that the error in the data was too significant, accounting for 42%. Laboratory inspection on water samples concluded that the water quality feeding to the UF membranes was worse than that of the raw water. This led to a conclusion that severe contamination occurred within the main feed tank where the water was retained before arriving to the UF modules. The type of contamination present in the feed tank is yet to be investigated. Though, frequent cleaning or flushing of the feed tank is recommended on regular basis.

This study investigates the operation of dual media filter DMF during ambient and simulated algal bloom conditions, and the role of coagulation and dissolved air flotation (DAF) in mitigating the adverse effects of algal blooms on DMF performance. The study also highlights which AOM concentration as a function of biopolymer is critical to organic fouling in DMF pretreatment for Red Sea water desalination with RO. On the other hand, the present study has carried out another experiment on AOM fouling in comparison with bacterial organic matter (BOM) and humic organic matter (HOM) using two different pore sizes of UF ceramic membranes, 5 and 50 kDa. The main aim of this comparison is to examine fouling behavior and mechanism and removal efficiency. The study revealed that AOM can induce organic fouling in DMF during simulated algal bloom conditions at biopolymer concentrations as low as 0.2 mg C/L. DMF performance was strongly affected by AOM concentration as observed by flow rate decline through time. Liquid chromatography – organic carbon detection (LC-OCD) analysis showed higher removal rates of biopolymers than lower molecular weight fractions (i.e., humic substances, building blocks and low molecular weight neutrals) for all pretreatment scenarios. The study also indicated that while DMF performance was enhanced with coagulation and sedimentation, the most significant improvement in performance was observed for DMF operation preceded by coagulation and DAF. Hydraulic performance of DMF correlated well with biopolymers removal, with removal rates of 72%, 53% and 39%, for coagulation/DAF, coagulation/sedimentation, and no coagulation, respectively. For UF ceramic membranes, results showed that more TEP/organics were removed by the 5 kDa membranes compared to the 50 kDa membrane, which is accounted for lower MWCO. The UF 5 kDa membrane also showed low fouling formation than 50 kDa membrane for all of three types of organic matter tested. Analysis of the fouled membranes by SEM images showed that fouling was dominated by cake layer formation for the 5 kDa membrane while pore blockage followed by cake layer formation is apparent for the 50 kDa membrane.

Water samples were taken at the KAUST RO plant, the WDRC pilot plant and three other full-scale desalination installations in Saudi Arabia. The water was characterized using selected microbiological parameters, being conventional (heterotopic place count (HPC), total coliforms, Escherichia coli) and more novel and sensitive methods (adenosine tri-phosphate (ATP, a measure for bacterial activity), as well as total and intact bacterial cell concentrations (TDC using flow cytometry) and supporting parameters (pH, conductivity, residual chlorine and temperature). Selective samples were used to quantify the bacterial growth potential (“food for the bacteria”), applying a flow cytometer based easily Assimilable Organic Carbon (AOC) assay. Hypothesized was that no or very low bacterial numbers would occur after RO filtration in the plants due to the high rejection properties of the RO membranes and the produced water exceptionally low mineral and nutrient content. Key findings are that the (i) RO permeate contains bacterial cell concentrations exceeding 1.0 × 103 cells/mL. The highest percentage of cells are intact and active, based on the ATP and total cell counts (ii) advanced microbial parameters ATP and TDC enabled to detect and quantify bacteria numbers and activity while the less sensitive conventional plate counts based techniques did not, (iii) flow cytometer-based growth potential measurements indicate the presence of 8 µg AOC/L in the RO permeate. A typical last step in drinking water production is chlorination, effectively inactivating all the bacterial cells. The origin of the bacterial cells and the biodegradable nutrients enabling the bacterial growth in the RO permeate is not clear. There is a clear need to assess the origin of the nutrients and bacteria found in the RO produced water. It is not expected to be passing the RO membrane.

Desalination is considered to be a major source of usable water in the Middle East, especially the Gulf countries which lack fresh water resources. A key and sometimes the only solution to produce high quality water in these countries is through the use of seawater reverse osmosis (SWRO) desalination technology. Membrane fouling is an economic and operational defect that impacts the performance of SWRO desalination technology. To limit this fouling phenomenon, it is important to implement the appropriate type of intake and pre-treatment system design. In this study, two types of systems were investigated, a vertical well system and a surface-water intake at a 9m depth. The purpose of this investigation is to study the impact of the different intake systems and pre-treatment stages in minimizing the concentrations of algae, bacteria, natural organic matter (NOM) and transparent exopolymer particles (TEP), in the feed water prior to pre-treatment, through the pre-treatment stages, and in the product water and concentrate. Water samples were collected from the surface seawater, the intakes (wells for site A, 9 m depth open ocean intake at site B), after the media filter, after the cartridge filter, and from the permeate and reject streams. The measured parameters included physical parameters, algae, bacteria, total organic carbon (TOC), fractions of dissolved NOM, particulate and colloidal TEP. The results of this study prove that the natural filtration and biological treatment of the seawater which occur in the aquifer matrix are very effective in improving the raw water quality to a significant degree. The results demonstrated that algae and biopolymers were 100% removed, the bacterial concentrations were significantly removed and roughly 50% or greater of TOC concentrations was eliminated by the aquifer matrix at site A. The aquifer feeding the vertical wells reduced TEP concentrations, but to differing degree. There is a slight decrease in the concentrations of, algae, bacteria, TOC, NOM, and TEP in the feed water at 9 m depth compared to the surface seawater at site B. The pre-treatment was of significant effectiveness and the improvements in reducing the membrane fouling potential were quite high and strong at this site. Investigation of the permeate stream showed some breakthrough of bacteria which is of concern because it may indicate a problem within the membrane system (e.g., broken seal and perforation). The aquifer feeding the wells in the subsurface system plays a main role in the improvement of water quality, so the pre-treatment seems less effective in site A plant. This proves that the subsurface intake is better than open ocean intake in terms of providing better raw water quality and ultimately reducing membrane biofouling.

Subsurface intake systems are known to improve the feed water quality for SWRO plants. However, a little is known about the feasibility of implementation in coastal settings, the degree of water quality improvements provided by these systems, and the internal mechanisms of potential fouling compounds removal within subsurface intake systems. A new method was developed to assess the feasibility of using different subsurface intake systems in coastal areas and was applied to Red Sea coastline of Saudi Arabia. The methodology demonstrated that five specific coastal environments could support well intake systems use for small-capacity SWRO plants, whereas large-capacity SWRO facilities could use seabed gallery intake systems. It was also found that seabed intake system could run with no operational constraints based on the high evaporation rates and associated diurnal salinity changes along the coast line. Performance of well intake systems in several SWRO facilities along the Red Sea coast showed that the concentrations of organic compounds were reduced in the feed water, similar or better than traditional pretreatment methodologies. Nearly all algae, up to 99% of bacteria, between 84 and 100% of the biopolymer fraction of NOM, and a high percentage of TEP were removed during transport through the aquifer. These organics cause membrane biofouling and using well intakes showed a 50-75% lower need to clean the SWRO membranes compared to conventional open-ocean intakes. An assessment of the effectiveness of seabed gallery intake systems was conducted through a long-term bench-scale column experiment. The simulation of the active layer (upper 1 m) showed that it is highly effective at producing feed water quality improvements and acts totally different compared to slow sand filtration systems treating freshwater. No development of a “schmutzdecke” layer occurred and treatment was not limited to the top 10 cm, but throughout the full column thickness. Algae and bacteria were removed in a manner similar to slow sand filtration, but it took many months to produce consistent reductions in NOM fractions and TEP. The data suggested that a thicker active layer (2m) is needed to facilitate a more rapid reduction in the main potential fouling organics.

Shuqaiq-II IWP is a combined RO water desalination and power plant facility. It operates with an open intake that feeds the plant with 100,000 m3/h of raw water. The facility is located 140 km north of Jizan, in a small bay where the run-off discharges of two wadis converge. The run-off coming from the wadis are rich in alluvial sediments that dramatically decrease the raw water quality at the intake point, causing periodic shutdowns of the plant and increasing the operational cost due to membrane replacement. Subsurface water intakes are an alternative for improving raw water quality, as they provide natural filtering of the feed water as it flows through the systems. In this type of system water flow through the sediment matrix is induced and during the percolation, several physical, chemical and biological processes take place, cleaning the water from particulate matter, resulting in high quality feed water that can be directly sent to the RO process without any additional pretreatment. A full hydrogeological profile of the seabed needs to be performed in order to determine the applicability of one of these systems in each particular location. In this study, 1 km of beach area at Shuqaiq-II IWP was surveyed. Ninety-one (91) samples from the shore and offshore sediments were collected and analyzed for hydraulic conductivity, porosity and grain size distribution. The laboratory analysis showed that the construction of the seabed galleries was technically feasible, and the proposed intake system was design to meet the feed water requirements for the RO facility (530.000 m3/d). The preliminary design consists of 17 cells in total, 16 of which will be in constant operation, and 1 alternate for whenever maintenance is needed in one of the other cells. The seabed gallery design includes 5 layers of sands with a total depth of 5 m. A detailed underdrain design methodology is presented. The system would be operated at an infiltration rate of 10 m/d and an average hydraulic retention time of 7h. Each cell will have an area of 3.500 m2 that will supply 35.000 m3/d of feed water to each RO train.