Abdullah H.A. Dehwah

Determination of Hydraulic Conductivity from Grain-Size Distribution for Different Depositional Environments

Over 400 unlithified sediment samples were collected from four different depositional environments in global locations and the grain-size distribution, porosity, and hydraulic conductivity were measured using standard methods. The measured hydraulic conductivity values were then compared to values calculated using 20 different empirical equations (e.g., Hazen, Carman-Kozeny) commonly used to estimate hydraulic conductivity from grain-size distribution. It was found that most of the hydraulic conductivity values estimated from the empirical equations correlated very poorly to the measured hydraulic conductivity values with errors ranging to over 500%. To improve the empirical estimation methodology, the samples were grouped by depositional environment and subdivided into subgroups based on lithology and mud percentage. The empirical methods were then analyzed to assess which methods best estimated the measured values. Modifications of the empirical equations, including changes to special coefficients and addition of offsets, were made to produce modified equations that considerably improve the hydraulic conductivity estimates from grain size data for beach, dune, offshore marine, and river sediments. Estimated hydraulic conductivity errors were reduced to 6 to 7.1 m/day for the beach subgroups, 3.4 to 7.1 m/day for dune subgroups, and 2.2 to 11 m/day for offshore sediments subgroups. Improvements were made for river environments, but still produced high errors between 13 and 23 m/day.

Use of beach galleries as an intake for future seawater desalination facilities in Florida and globally similar areas

AbstractDesalination of seawater using the reverse osmosis process can be made less costly by the use of subsurface intake systems. Use of conventional open-ocean intakes requires the addition of a number of pretreatment processes to protect the primary RO process. Despite using the best designs possible for the pretreatment, seawater RO membranes tend to biofoul because of the naturally-occurring organic material and small bacteria present in seawater. These materials are not completely removed by the pretreatment system and they pass through the cartridge filters into the membranes, thereby causing frequent and expensive cleaning of the membranes. Quality of the raw water can be greatly improved by the use of subsurface intakes which can substantially reduce the overall treatment cost. There are a number of possible subsurface designs that can be used including conventional vertical wells, horizontal wells, collector wells, beach galleries, and seabed filters. The key selection criteria for the type of ...

Technical feasibility of using gallery intakes for seawater RO facilities, northern Red Sea coast of Saudi Arabia: the King Abdullah Economic City site

AbstractThe Kingdom of Saudi Arabia is dependent on desalination of seawater to provide new water supplies for the future. Desalination is expensive and it is very important to reduce the cost and lower the energy consumption. Most seawater reverse osmosis facilities use open-ocean intakes, which require extensive pretreatment processes to remove particulate and biological materials that cause operating problems such as membrane fouling or shutdown during algal blooms. Subsurface systems, using the concept of riverbank filtration, can be used as intakes. These systems include wells of various designs and galleries that provide natural filtration and biological treatment to improve the quality of feed water before it enters the desalination plant. This reduces operating cost, lowers chemical and energy consumption, and reduces environmental impacts. Technical feasibility of gallery-type intakes, beach and seabed types, for use as intakes to seawater reverse osmosis (RO) facilities was evaluated along the n...

Subsurface intake systems: Green choice for improving feed water quality at SWRO desalination plants, Jeddah, Saudi Arabia

An investigation of three seawater reverse osmosis facilities located along the shoreline of the Red Sea of Saudi Arabia that use well intake systems showed that the pumping-induced flow of raw seawater through a coastal aquifer significantly improves feed water quality. A comparison between the surface seawater and the discharge from the wells shows that turbidity, algae, bacteria, total organic carbon, most fractions of natural organic matter (NOM), and particulate and colloidal transparent exopolymer particles (TEP) have significant reductions in concentration. Nearly all of the algae, up to 99% of the bacteria, between 84 and 100% of the biopolymer fraction of NOM, and a high percentage of the TEP were removed during transport. The data suggest that the flowpath length and hydraulic retention time in the aquifer play the most important roles in removal of the organic matter. Since the collective concentrations of bacteria, biopolymers, and TEP in the intake seawater play important roles in the biofouling of SWRO membranes, the observed reductions suggest that the desalination facilities that use well intakes systems will have a potentially lower fouling rate compared to open-ocean intake systems. Furthermore, well intake system intakes also reduce the need for chemical usage during complex pretreatment systems required for operation of SWRO facilities using open-ocean intakes and reduce environmental impacts.

Impact of well intake systems on bacterial, algae, and organic carbon reduction in SWRO desalination systems, SAWACO, Jeddah, Saudi Arabia

AbstractThe intake system can play a significant role in improving the feed water quality and ultimately influence the performance of downstream components of the seawater reverse osmosis desalination processes. In most cases, open-ocean intakes produce poor feed water quality in terms of the abundance of naturally occurring organic matter, which increases the risk of membrane fouling. An alternative intake is the subsurface system, which is based on the riverbank filtration concept that provides natural filtration and biological treatment of the feed water prior to the entry of the water into the desalination plant. The use of subsurface intakes normally improves the raw water quality by reducing suspended solids, algae, bacterial, and dissolved organic carbon concentrations. Therefore, the risk of biofouling caused by these substances can be reduced by implementing the appropriate type of intake system. The use of well intake systems was investigated along the Red Sea shoreline of Saudi Arabia in the Je...

Feasibility of using a subsurface intake for SWRO facility, south of Jeddah, Saudi Arabia

The Kingdom of Saudi Arabia is the largest producer of desalinated water with about 13% of the global desalination capacity. Most of these desalination plants use the open-ocean intakes to deliver ...

Aquifer Treatment of Sea Water to Remove Natural Organic Matter Before Desalination

An investigation of a sea water reverse osmosis desalination facility located in western Saudi Arabia has shown that aquifer treatment of the raw sea water provides a high degree of removal of natural organic matter (NOM) that causes membrane biofouling. The aquifer is a carbonate system that has a good hydraulic connection to the sea and 14 wells are used to induce sea water movement 400 to 450 m from the sea to the wells. During aquifer transport virtually all of the algae, over 90% of the bacteria, over 90% of the biopolymer fraction of NOM, and high percentages of the humic substance, building blocks, and some of the low molecular weight fractions of NOM are removed. Between 44 and over 90% of the transparent exopolymer particles (TEP) are removed with a corresponding significant reduction in concentration of the colloidal fraction of TEP. The removal rate for TEP appears to be greater in carbonate aquifers compared to siliciclastic systems. Although the production wells range in age from 4 months to 14 years, no significant difference in the degree of water treatment provided by the aquifer was found.

Effects of Well Intake Systems on Removal of Algae, Bacteria, and Natural Organic Matter

Analyses of the changes in concentration of algae, bacteria, transparent exopolymer particles (TEP), and the fractions of natural organic matter (NOM) impacts between surface seawater and the discharges of well intake systems were evaluated at seven different seawater reverse osmosis water (SWRO) treatment plants. In nearly all cases, travel of the raw seawater through the seabed into the aquifer and into the wells removed all of the algae. Bacteria removal was up to 98.5 %, but varied greatly between sites and in different wells at each site. The TEP concentration was significantly lowered compared to the natural seawater. The biopolymer fraction of NOM was significantly lowered at all sites, but the lighter fractions of the NOM were removed at lower percentages. The removal percentage of NOM fractions appears to be based on molecular weight (and size) with the lighter weight fractions removed at lower percentages. A key factor controlling the removal of organic material appears to by the hydraulic retention time which is controlled by the length of the flowpath and the type of aquifer porosity. Specific site geology does not seem to be a significant factor. Vertical well systems showed greater organic materials removal compared to horizontal and tunnel intake systems. Again, this appears to be related to the length of the flowpath and the hydraulic retention time. The horizontal well system at Alicante, Spain showed poor removal of organic matter and breakthrough of algae occurred in the system.

Effects of Intake Depth on Raw Seawater Quality in the Red Sea

It has been suggested that using a deep open-ocean intake would improve feed water quality and would reduce the cost of SWRO water treatment by lessening membrane biofouling potential. The feasibility of developing deep intake systems for large-capacity SWRO plants located on the Red Sea was assessed. A bathymetric survey showed that the continental shelf along the Red Sea nearshore has a nearly vertical drop into deep water beginning at depths between 20 and 40 m. The vertical nature of the bathymetric profile and the issue of active seismicity make the development of a SWRO intake at a depth of greater than 100 m below surface a very risky venture along the Red Sea coast of Saudi Arabia. Detailed assessment of temperature and salinity with depth show a decrease of 5 °C and an increase of 1100 mg/L respectively over 90 m. Concentrations of algae, bacteria, total organic carbon, particulate and colloidal TEP, and the biopolymer fraction of natural organic carbon all showed declines in concentration. However, the general water quality improvements in reduced concentrations of organic matter were insufficient to reduce the intensity of pretreatment for an SWRO system. Overall, the Red Sea does not appear to be a good location for the use of deep SWRO intakes because of the structural risk of installing and maintaining an intake at near or below 100 m of water depth.

Coastal Evaluation and Planning for Development of Subsurface Intake Systems

The feasibility of using a subsurface intake system for a seawater reverse osmosis (SWRO) water treatment plant is based on the site-specific hydrogeologic conditions which control the type of intake design that can be used and the capacity of the intake. Planning for future development of subsurface intake systems requires a careful analysis of the shoreline and shallow offshore area. Example regions, the Red Sea coast of Saudi Arabia and the shoreline of Florida (USA), were investigated to develop general feasibility criteria for possible development of SWRO intake systems. Within the Red Sea, it was found that various well intake systems could be feasible for low-capacity SWRO facilities and high capacity intake systems would be limited to seabed gallery intakes. Coastal Florida had more subsurface intake options available, including wells, beach galleries, and seabed galleries which could be used based on the required capacity and the specific site conditions. The presence of high transmissivity carbonate aquifers containing seawater in Florida would allow medium capacity SWRO systems to use conventional vertical wells. High capacity systems could be developed using beach gallery systems in many locations. The methods developed for shoreline and nearshore evaluation contained herein could be applied to any coastal region of the world for subsurface intake evaluation.