Seawater Reverse Osmosis Facilities Research Articles

Techno-economic feasibility of photovoltaic solar electrodialysis with bipolar membranes

Electrodialysis with bipolar membranes (EDBM) can transform concentrated brines into acids and bases through the application of an electric field. Nevertheless, the widespread use of EDBM is limited by its high energy consumption, typically based on fossil fuels. Yet, the integration of EDBM with renewable energy sources, like solar photovoltaic (PV), remains unexplored. This study presents a techno-economic analysis of PV-EDBM to produce NaOH and HCl from seawater reverse osmosis (SWRO) brines. An integrated PV-EDBM model was developed and applied to a hypothetical PV-EDBM plant located in the SWRO facility of Lampedusa (Italy). Results revealed that PV has no negative impact on the performance in terms of product concentration, specific energy consumption and current efficiency. Meanwhile, the levelized cost of NaOH for PV-EDBM was reduced by 20 % in comparison to the electrical grid mix, achieving 210 €·ton−1 NaOH on an annual average for PV-EDBM. Therefore, the investment associated with PV is offset by the benefits of reduced electricity costs from the grid. Consequently, EDBM emerges as a feasible solution to address resource scarcity, representing a significant step towards integrating renewable energies with advanced wastewater treatment technologies, thus paving the path to a greener future.

Technical and Environmental Feasibilities of the Commercial Production of NaOH from Brine by Means of an Integrated EDBM and Evaporation Process.

Electrodialysis with bipolar membranes (EDBMs) is a technology that offers a great potential for the introduction of the principles of a circular economy in the desalination industry, by providing a strategy for the recovery of HCl and NaOH from brine via the process of seawater reverse osmosis (SWRO). Both chemicals are widely employed in desalination facilities, however NaOH presents a special interest due to its higher requirements and cost. Nevertheless, the standard commercial concentrations that are commonly employed in the facilities cannot be obtained using the state of the art EDBM technology itself. Therefore, the aim and main purpose of this work is to prove the technical and environmental feasibilities of a new approach to produce commercial NaOH (50%wt.) from SWRO brine by means of an integrated process of EDBMs followed by a triple effect evaporation. The global process has been technically evaluated in terms of the specific energy consumption (SEC) (kWh·kg−1 NaOH) and the environmental sustainability performance has been analyzed by its carbon footprint (CF) (kg CO2-eq.·kg−1 NaOH). The influence of the current density, and the power source in the EDBM stage have been evaluated on a laboratory scale while the influence of the feed stream concentration in the evaporation stage has been obtained through simulations using Aspen Plus. The lowest SEC of the integrated process (SECOV), 31.1 kWh·kg−1 NaOH, is obtained when an average current density of 500 A·m−2, provided by a power supply (grid mix), is applied in the EDBM stage. The environmental burdens of the integrated process have been quantified by achieving reductions in the CF by up to 54.7% when solar photovoltaic energy is employed as the power source for EDBMs, with a value of 5.38 kg CO2-eq.·kg−1 NaOH. This study presents a great potential for the introduction of the principles of a circular economy in the water industry through the recovery of NaOH from the high salinity waste stream generated in SWRO facilities and opens the possibility of the reuse of NaOH by its self-supply in the desalination plant.

Economics and Energy Consumption of Brackish Water Reverse Osmosis Desalination: Innovations and Impacts of Feedwater Quality.

Brackish water desalination, using the reverse osmosis (BWRO) process, has become common in global regions, where vast reserves of brackish groundwater are found (e.g., the United States, North Africa). A literature survey and detailed analyses of several BWRO facilities in Florida have revealed some interesting and valuable information on the costs and energy use. Depending on the capacity, water quality, and additional scope items, the capital cost (CAPEX) ranges from USD 500 to USD 2947/m3 of the capacity (USD 690–USD 4067/m3 corrected for inflation to 2020). The highest number was associated with the City of Cape Coral North Plant, Florida, which had an expanded project scope. The general range of the operating cost (OPEX) is USD 0.39 to USD 0.66/m3 (cannot be corrected for inflation), for a range of capacities from 10,000 to 70,000 m3/d. The feed-water quality, in the range of 2000 to 6000 mg/L of the total dissolved solids, does not significantly impact the OPEX. There is a significant scaling trend, with OPEX cost reducing as plant capacity increases, but there is considerable scatter based on the pre- and post-treatment complexity. Many BWRO facilities operate with long-term increases in the salinity of the feedwater (groundwater), caused by pumping-induced vertical and horizontal migration of the higher salinity water. Any cost and energy increase that is caused by the higher feed water salinity, can be significantly mitigated by using energy recovery, which is not commonly used in BWRO operations. OPEX in BWRO systems is likely to remain relatively constant, based on the limitation on the plant capacity, caused by the brackish water availability at a given site. Seawater reverse osmosis facilities, with a very large capacity, have a lower OPEX compared to the upper range of BWRO, because of capacity scaling, special electrical energy deals, and process design certainty.

Organic compounds and microbial assessment of a seawater reverse osmosis facility at Tampa Bay Water, USA

The Tampa Bay Water seawater reverse osmosis (SWRO) facility is the first large-capacity seawater desalination plant in the United States. The feedwater source for the facility is an estuarine system that is biologically very productive and contains naturally-occurring high concentrations of algae, marine bacteria, total organic carbon (mostly dissolved), transparent exopolymer particles (TEP), the biopolymer fraction of natural organic matter, and phosphate. The high-organic composition of the feedwater places stress on the conventional sand pretreatment system utilized at the facility resulting in high organic passage into the membrane process and flow through into the permeate. In particular, the direct passage of particulate TEP (p-TEP) into the membranes has a major impact on the biofouling rate. Based on the data collected, the pretreatment is ineffective at removing key organic components that impact the rate of membrane biofouling, particularly bacteria and p-TEP. Perhaps the pretreatment could be re-designed to use a dissolved air floatation system (DAF) followed by ultrafiltration as a remedy that would likely move the biofouling problem to the ultrafiltration process, which has an easier cleaning process. Consideration could be given to using a groundwater source of feedwater as a permanent remedy to the operational issues.

Potential biofoulants in open-ocean SWRO desalination station in Jeddah, KSA

Abstract Currently, water desalination is an essential solution for the high demand for water worldwide. A sea water reverse osmosis (SWRO) facility fulfills the need for pure water. Conventionally, these plants use open-ocean water that is rich with natural organic matter (NOM) and transparent exo-polymers (TEP). Marine flora increases the demand for fouling the membrane in the SWRO facility that raises the pressure and results in the halting of the station. Therefore, water samples were collected from SWRO stages during high-pressure problems to probe the factors that play a key role in membrane biofouling. NOM and TEP particles physically disappeared after the dual-media filter (DMF). However, turbidity significantly increased after the DMF stage, which is indicative of the fragmentation of NOM and TEP particles. Chlorophyll and phycoerythrin disappeared after the DMF stage but were observed in the reject stage (brine). Therefore, NOM and TEP are playing a role indirectly in membrane biofouling. Fifteen potential species of heterotrophic prokaryotes are identified and recorded in all stages of the SWRO. The characteristics of these species imply that they form a cooperative consortium that potentially creates the biofilm in the RO membrane. Therefore, SWRO facilities that use open-ocean water must develop highly sophisticated pretreatment technology to eliminate the seeds of the biofilm that fouls RO membranes.

Seabed gallery intakes: Investigation of the water pretreatment effectiveness of the active layer using a long-term column experiment

Seabed gallery intake systems used for seawater reverse osmosis facilities employ the same principle of water treatment as slow sand filtration in freshwater systems. An investigation concerning the effectiveness of the active layer (top layer) in improving raw water quality was conducted by using a long-term bench-scale columns experiment. Two different media types, silica and carbonate sand, were tested in 1 m columns to evaluate the effectiveness of media type in terms of algae, bacteria, Natural Organic Matter (NOM) and Transparent Exopolymer Particles (TEP) removal over a period of 620 days. Nearly all algae in the silica sand column, 87% (σ = 0.04) of the bacteria, 59% (σ = 0.11) of the biopolymer fraction of NOM, 59% (σ = 0.16) of particulate and 32% (σ = 0.25) of colloidal TEP were removed during the last 330 days of the experiment. Total removal was observed in the carbonate sand column for algal concentration, while the bacterial removal was lower at 74% (σ = 0.08). Removal of biopolymers, particulate and colloidal TEP were higher in the carbonate column during the last 330 days with 72% (σ = 0.15), 66% (σ = 0.08) and 36% (σ = 0.12) removed for these organics respectively. Removal of these key organics through the 1 m thick column, representing the active layer, will likely reduce the rate of biofouling, reduce chemical usage and minimize operating cost in SWRO systems. The data show that the media will require several months at the beginning of operation to reach equilibrium so that high organic removal rates can be achieved. No development of a “schmutzdecke” layer occurred. The experimental results suggest that unlike freshwater slow sand filtration wherein most water treatment occurs in the upper 10 cm, in seawater systems treatment occurs throughout the full active layer depth of 1 m. The results of this study will help in designing and operating seabed gallery intake systems in varied geological conditions.

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.

Changes in feedwater organic matter concentrations based on intake type and pretreatment processes at SWRO facilities, Red Sea, Saudi Arabia

Transparent exopolymer particles (TEP), natural organic matter, and bacterial concentrations in feedwater are important factors that can lead to membrane biofouling in seawater reverse osmosis (SWRO) systems. Two methods for controlling these concentrations in the feedwater prior to pretreatment have been suggested; use of subsurface intake systems or placement of the intake at a greater depth in the sea. These proposed solutions were tested at two SWRO facilities located along the Red Sea of Saudi Arabia. A shallow well intake system was very effective in reducing the algae and bacterial concentrations and somewhat effective in reducing TEP concentrations. An intake placed at a depth of 9m below the surface was found to have limited impact on improving water quality compared to a surface intake. The algae and bacteria concentration in the feedwater (deep) was lower compared to the surface seawater, but the overall TEP concentration was higher. Bacteria and TEP measurements made in the pretreatment process train in the plant and after the cartridge filters suggest that regrowth of bacteria is occurring within the cartridge filters.

Hydrogeology, water quality, and microbial assessment of a coastal alluvial aquifer in western Saudi Arabia: potential use of coastal wadi aquifers for desalination water supplies

Wadi alluvial aquifers located along coastal areas of the Middle East have been assumed to be suitable sources of feed water for seawater reverse osmosis facilities based on high productivity, connectedness to the sea for recharge, and the occurrence of seawater with chemistry similar to that in the adjacent Red Sea. An investigation of the intersection of Wadi Wasimi with the Red Sea in western Saudi Arabia has revealed that the associated predominantly unconfined alluvial aquifer divides into two sand-and-gravel aquifers at the coast, each with high productivity (transmissivity = 42,000 m2/day). This aquifer system becomes confined near the coast and contains hypersaline water. The hydrogeology of Wadi Wasimi shows that two of the assumptions are incorrect in that the aquifer is not well connected to the sea because of confinement by very low hydraulic conductivity terrigenous and marine muds and the aquifer contains hypersaline water as a result of a hydraulic connection to a coastal sabkha. A supplemental study shows that the aquifer system contains a diverse microbial community composed of predominantly of Proteobacteria with accompanying high percentages of Gammaproteobacteria, Alphaproteobacteria and Deltaproteobacteria.

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

The 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 Jeddah region. Data were collected from a seawater reverse osmosis (SWRO) plant with a capacity of 10,000 m3/d. The well system produces feed water from an artificial-fill peninsula that was constructed atop of the seabed. Ten wells have been constructed on the peninsula for extracting raw seawater. Water samples were collected from nearby surface seawater as a reference and from selected individual wells. The percentage of algae and bacterial removal by induced filtration process was evaluated by comparison of the seawater concentrations with the well discharges. Transparent exopolymer particles and organic carbon fractions reduction was also measured. The quality of raw water extracted from the well systems was highly improved compared with the raw seawater source. It was observed that algae were virtually 100% removed and the bacterial concentration was significantly removed by the aquifer matrix. The detailed analysis of organic carbon fraction using liquid chromatography-organic carbon detection instrument showed a high-percentage removal of the organic fractions consummate with the molecular weight. The results of this study can be used to improve the intake system design of existing SWRO facilities that might require expansion in future or new facilities that will be located along the Red Sea coastline.

Technical feasibility of a seabed gallery system for SWRO facilities at Shoaiba, Saudi Arabia, and regions with similar geology

AbstractSubsurface intakes can be used as part of the pretreatment system for seawater reverse osmosis facilities. Wells of various designs and galleries are being used for intakes at many sites globally to reduce pretreatment costs, chemical usage, biofouling potential, and environmental impacts (entrainment and impingement). The goal of using a subsurface intake is to reduce or replace conventional pretreatment processes. A field and laboratory investigation was undertaken to assess the feasibility of developing a seabed gallery intake offshore near the Shoaiba seawater RO (SWRO) plant site (150,000 m3/d treatment capacity) that could be used to replace the current intake used for only the RO capacity. A survey of the beach and offshore area was made and 51 sediment samples were collected from the seabed for laboratory analysis of grain size distribution, porosity, and hydraulic conductivity. Field observations showed that the marine bottom has a low slope from the shoreline seaward a distance of about ...

Subsurface intakes for seawater reverse osmosis facilities: Capacity limitation, water quality improvement, and economics

The use of subsurface intake systems for seawater reverse osmosis (SWRO) desalination plants significantly improves raw water quality, reduces chemical usage and environmental impacts, decreases the carbon footprint, and reduces cost of treated water to consumers. These intakes include wells (vertical, angle, and radial type) and galleries, which can be located either on the beach or in the seabed. Subsurface intakes act both as intakes and as part of the pretreatment system by providing filtration and active biological treatment of the raw seawater. Recent investigations of the improvement in water quality made by subsurface intakes show lowering of the silt density index by 75 to 90%, removal of nearly all algae, removal of over 90% of bacteria, reduction in the concentrations of TOC and DOC, and virtual elimination of biopolymers and polysaccharides that cause organic biofouling of membranes. Economic analyses show that overall SWRO operating costs can be reduced by 5 to 30% by using subsurface intake systems. Although capital costs can be slightly to significantly higher compared to open-ocean intake system costs, a preliminary life-cycle cost analysis shows significant cost saving over operating periods of 10 to 30years.

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...

The availability and security of water production using reliable energy recovery technologies

Abstract The term availability can be defined as the probability of a system or piece of equipment, when used under the specified conditions, operates satisfactorily at any given time. The availability of the equipment installed in a seawater reverse osmosis (SWRO) facility is extremely important to the price, quality, and quantity of the final product—water. There are three critical components in the SWRO processes; the main high-pressure feed pumps, the reverse osmosis (RO) membranes, and the energy recovery device (ERD) system. The role that ERDs play is undeniably critical to the success or failure of an RO facility’s ability to produce and deliver water economically. The largest operating expense for an SWRO facility is the power consumed, which accounts for approximately 30% of the total RO operating expense. Typically for large facilities (>50,000 m3/d), the ERDs responsible for reducing energy consumption are only 1–2% of the entire initial capital cost—a small fraction—but one that can offer a substantial return on investment through energy savings. Selecting the proper ERD system can save millions of dollars over the life of a plant and provide owners and operators with a secure and reliable means of water production. This paper will focus on the economic benefits and importance of the availability of ERDs in SWRO desalination plants.

Unprecedented system efficiency and simplicity yields exceptionally low cost of permeate in 5,000 ton/day SWRO system

ABSTRACT The rising cost of energy has put extreme pressures on the design and operation of municipal seawater reverse osmosis (SWRO) facilities especially in localities where electricity rates are high. To meet this challenge, creative approaches to SWRO system design and energy recovery devices (ERD) selection and utilization are required. Any successful approach will have to take into consideration not only the energy transfer efficiency of the particular ERD, but its level of complexity, ease of start-up, and capital costs in order to build a system with the lowest possible specific energy consumption (SEC). This paper will describe how a 4,500 m3/day municipal SWRO facility with energy costs exceeding 0.28 kH-h and an ERD supplier recently met this challenge and produced a system with a SEC of < 2.46 kW-h/m3. The first section of this paper will review three ERD technologies available on the market today: the Pelton impulse turbine; isobaric chambers; and hydraulic pressure boosters. Attention will b...

Titan PX-1200 Energy Recovery device — test results from the Inima Los Cabos, Mexico, seawater RO facility

The Energy Recovery, Inc. (ERI®) PX Pressure Exchanger® energy recovery device recovers hydraulic energy from the high-pressure reject stream from a reverse osmosis (RO) system and transfers it to low-pressure feedwater. Pressurized feedwater from the PX device is sent to the membrane feed, merging with a stream of pressurized water from a high-pressure pump. This significantly reduces the duty of the high-pressure pump. The PX device operates at extremely high efficiency—up to 98% — and itself consumes no electrical power. Therefore, the overall energy consumption of a seawater RO process is cut in half or less compared to a system operating with no energy recovery or by 15 to 30% compared to a system operating with state-of-the-art centrifugal energy recovery devices. In addition, PX technology gives the operator the flexibility to vary the RO system recovery rate to maximize process productivity and energy efficiency over a wide range of feed conditions. The first PX device sold commercially in 1997—th...

Enhancing boron rejection in seawater reverse osmosis facilities

Linked to potential health problems and toxicity to crops, boron is present in seawater at concentrations of ranging from 4 to 7 mg/L, and not readily removed by reverse osmosis technology. Commercially available seawater reverse osmosis (SWRO) membranes possess a wide range of rejection characteristics for boron in seawater under ambient temperature and pH, ranging from approximately 50% for low-energy membranes to greater than 90% for the newest high rejection membranes. This level of rejection is typically insufficient to reduce boron concentrations in natural seawater to less than recommended levels. Current World Health Organization (WHO) drinking water concentrations for boron are limited to 0.5-mg/L. Two techniques utilized to mitigate boron concentrations are (1) increasing the dissociation of boric acid by increasing pH prior to SWRO; and, (2) utilizing a second pass reverse osmosis system, potentially coupled with pH adjustment. Utilizing these techniques, the authors tested commercially available SWRO membranes from three different manufacturers utilizing feed water alkalization, coupled with a second pass system. Utilizing feed water alkalization alone, the authors found that all three SWRO membranes were able to produce permeate complying with WHO regulations. Using second pass RO, a boron concentration of less than 0.5 mg/L was achieved for feed pH greater than 6, and less than 0.1-mg/L for pH of 10.

The malta seawater RO facility

The Polymetrics seawater reverse osmosis (RO) facility at Ghar Lapsi, Malta, is one of the largest seawater RO plants in the world, with an installed capacity of 20,000 m 3 /d (5.3 U.S. mgd). A second plant, provided under the same contract, has a capacity of 4,500 m 3 /d (1.2 U.S. mgd), utilizing highly brakish feedwater. The plants supply potable water for the island's 350,000 residents and its growing tourist trade. The seawater plant is a single pass design, utilizing DuPont permeators and is the first major installations incorporating energy recovery turbo-pumps. This paper summarizes the plant design, manufacture, assembly, and installation, and also reports up-to-date operation and maintenance data. The operating costs are presented.

The malta seawater reverse osmosis facility

The Polymetrics seawater reverse osmosis facility at Ghar Lapsi, Malta is one of the largest seawater RO plants in the world, with an installed capacity of 20,000 cubic meters per day (5.3 US mgd). The seawater plant, as well as a 4540 cubic meters per day (1.2 US mgd) brackish plant located at another Malta site, and supplied under the same contract, were scheduled to be operational in late 1982. The plants will supply potable water for the island's 350,000 residents and its growing tourist trade. The seawater plant is a single pass design, utilizing Du Pont permeators and is the first major installation incorporating high pressure energy recovery turbo-pumps. This paper will summarize the plant design, manufacture, assembly and installation by Polymetrics as well as report up-to-date operation and maintenance data.