Seawater Reverse Osmosis Desalination Research Articles

Biofouling in seawater reverse osmosis (SWRO): Impact of module geometry and mitigation with ultrafiltration

Since no pretreatment method is foolproof for the removal of foulants in reverse osmosis (RO) systems, the aim is to keep the production process efficiency as high as possible. In the vast majority of RO desalination plants, biofouling of membranes is considered as one of the most common operational problems. In this study, a full-scale seawater reverse osmosis (SWRO) desalination plant which was subject to severe biofouling was investigated. Autopsy showed higher biofilm concentrations near the inlet of the module likely due to the abundancy of nutrients. CFD simulation was also used to realize how the geometry of the module inlet could impact the flow within the membrane leaves and thus biofouling. A pilot-scale system including silicon carbide ultrafiltration (SiC-UF) membranes was established in order to filter biological matters. According to the results of this study, SiC-UF membranes appeared to be a reliable pretreatment method for removing almost 100% of all micro-organisms.

A comparison of gravity-driven membrane (GDM) reactor and biofiltration + GDM reactor for seawater reverse osmosis desalination pretreatment

In this study, permeate quality, membrane performance, and microbial community in a gravity-driven microfiltration (GDM) reactor and a biofiltration (BF) + GDM reactor for seawater reverse osmosis (RO) desalination pretreatment were compared at both lab-scale and pilot-scale. The presence of BF column was more efficient in removing soluble organic substances by biosorption/biodegradation, leading to superior permeate quality from BF + GDM and subsequently lower RO fouling than GDM. Compared to the biofilm-saturated anthracite media, the granular activated carbon media in BF improved the assimilable organic substances removal in BF + GDM. Although less organic substances and microbial cells were accumulated on the membrane in BF + GDM, its permeate flux was 10–20% lower than GDM. Furthermore, BF lowered the amounts and diversity of prokaryotes (due to less organic substances) and eukaryotes (due to BF media rejection and lacking of prokaryotic preys) in the membrane biofilm of BF + GDM, but did not cause significant shifts of predominant species. Thus, the lower flux in BF + GDM was attributed to the limited predation and movement of eukaryotes in membrane biofilm, which may result in the formation of less porous and compact biofilm layer. The cost analysis indicated that BF + GDM-RO requires 5.2% less operating cost and 1.5% less water production cost than GDM-RO.

Biological and Physical Effects of Brine Discharge from the Carlsbad Desalination Plant and Implications for Future Desalination Plant Constructions

Seawater reverse osmosis (SWRO) desalination is increasingly used as a technology for addressing shortages of freshwater supply and desalination plants are in operation or being planned world-wide and specifically in California, USA. However, the effects of continuous discharge of high-salinity brine into coastal environments are ill-constrained and in California are an issue of public debate. We collected in situ measurements of water chemistry and biological indicators in coastal waters (up to ~2 km from shore) before and after the newly constructed Carlsbad Desalination Plant (Carlsbad, CA, USA) began operations. A bottom water salinity anomaly indicates that the spatial footprint of the brine discharge plume extended about 600 m offshore with salinity up to 2.7 units above ambient (33.2). This exceeds the maximum salinity permitted for this location based on the California Ocean Plan (2015 Amendment to Water Quality Control Plan). However, no significant changes in the assessed biological indicators (benthic macrofauna, BOPA-index, brittle-star survival and growth) were observed at the discharge site. A model of mean ocean wave potential was used as an indicator of coastal mixing at Carlsbad Beach and at other locations in southern and central CA where desalination facilities are proposed. Our results indicated that to minimize environmental impacts discharge should target waters where a long history of anthropogenic activity has already compromised the natural setting. To ensure adequate mixing of the discharge brine desalination plants should be constructed at high-energy sites with sandy substrates, and discharge through diffusor systems.

Theoretical and experimental investigation of an absorption refrigeration and pre-desalination system for marine engine exhaust gas heat recovery

Absorption-refrigeration-cycle-based exhaust gas heat recovery technology is effective in improving the thermal efficiency and fuel economy of marine diesel engines. However, the absorption refrigeration system is inflexible in the start–stop operation, and this cannot fulfil the fluctuating demand of refrigeration. This paper presents both the theoretical and experimental investigations of an absorption refrigeration and freezing pre-desalination-based marine engine exhaust gas heat recovery system. The energy storage subcycle is introduced to overcome the energy underutilisation and balance the excessive refrigerating output of the absorption refrigeration cycle. Seawater is utilised as the phase-change material and it is pre-desalinated in the energy storage subcycle. A mathematical model of the system is established and experimental investigation is conducted. Furthermore, the theoretical and experimental performances are compared, and an economic analysis of seawater desalination is performed to evaluate its economy. The results show that the total refrigeration output of the system ranges from 6.1 kW to 9.9 kW, and the system COP (Coefficient of Performance) can reach 16% under the experimental operating conditions. Additionally, the salinity of pre-desalinated seawater can be reduced to below 10 ppt. Moreover, the cost of RO (Reverse Osmosis) seawater desalination can be reduced by 26% through the pre-desalination process of seawater.

The carbon footprint of desalination: An input-output analysis of seawater reverse osmosis desalination in Australia for 2005–2015

This study examines greenhouse gas emissions for 2005–2015 from seawater desalination in Australia, using conventional energies. We developed a tailor-made multi-regional input-output-model. We complemented macroeconomic top-down data with plant-specific desalination data of the largest 20 desalination plants in Australia. The analysed capacity cumulates to 95% of Australia's overall seawater desalination capacity. We considered the construction and the operation of desalination plants. We measure not only direct effects, but also indirect effects throughout the entire value chain. Our results show the following: We identify the state of Victoria with the highest emissions due to capital and operational expenditures (capex and opex). The contribution of the upstream value chain to total greenhouse gas emissions increases for capex and decreases for opex. For capex, the construction of intake and outfall is the driving factor for carbon emissions. For opex, electricity consumption is the decisive input factor. Both in construction and operation, we identify the critical role of the electricity sector for carbon emissions throughout the supply chain effects. The sector contributes 69% during the zenith of the construction phase and 96% during the operating phase to the entire emissions. We estimate the total emissions for 2015 at 1193 kt CO2e.

Chronic effects of brine discharge from large-scale seawater reverse osmosis desalination facilities on benthic bacteria

Seawater desalination facilities continuously discharge hyper-saline brine into the coastal environment which often flows as a concentrated plume over the seafloor, hence possibly impacting benthic microorganisms. Yet, the effects of brine discharge from desalination plants on benthic bacteria, key players in biodegradation of organic material and nutrient recycling is unknown. In this study, we tested the chronic (years) effects of brine discharge from three large-scale desalination facilities on the abundance, metabolic activity and community composition of benthic bacteria. To this end, four sampling campaigns were carried at the outfall areas of the Ashkelon, Sorek and Hadera desalination facilities. The effects of the brine were compared to corresponding reference stations which were not influenced by the brine (i.e., water temperature and salinity). Our sampling data indicate that bacterial abundance and activity that includes bacterial growth efficiency were 1.3–2.6-fold higher at the outfall area than the reference station. Concomitant analysis pointed out that the bacterial community structure at the brine discharge area was also different than the reference station, yet varied between each desalination facility. Our results demonstrate that the impact of brine effluent from desalination facilities on benthic bacteria are site-specific and localized (<1.4 Km2) around the discharge point. Namely, that the effects on benthic bacteria are prominent at the brine mixing zone and change according to the discharge method used to disperse the brine as well as local stressors (e.g., eutrophication and elevated water temperature). Our results contribute new insights on the effects of desalination-brine to benthic microbes, while providing scientifically-based aspects on the ecological impacts of brine dispersion for decision makers.

Multi‐objective performance optimization of irreversible molten carbonate fuel cell–Stirling heat engine–reverse osmosis and thermodynamic assessment with ecological objective approach

AbstractThis paper aims to investigate a hybrid cycle consisting of a molten carbonate fuel cell (FC) and a Stirling engine which, by connecting to a seawater reverse osmosis desalination unit, provides fresh water. First, a parametric evaluation is performed to study the effect of some key parameters, including the current density and the working temperature of the FC and the thermal conductance between the working substance and the heat reservoirs in the Stirling engine, on the objective functions. The objective functions include the energy efficiency, the exergy destruction rate density, the fresh water production rate, and the ecological function density. After investigating each double combination of these objective functions, two scenarios are defined in quest to concurrently optimize three functions together. The first scenario aims to optimize the energy efficiency, the exergy destruction rate density, and the fresh water production rate; and the second scenario attempts to optimize the energy efficiency, the fresh water production rate, and the ecological function density. A multi‐objective evolutionary algorithm joined with the nondominated sorting genetic algorithm (NSGA‐II) approach is employed to obtain Pareto fronts in each case scenario. In order to ascertain final solutions between Pareto fronts, three fast and robust decision‐making methods are employed including TOPSIS, LINMAP, and Fuzzy. Finally, a sensitivity analysis is conducted to critically analyze the performance of the system.

Techno-Economic Feasibility Study of a Hypersaline Pressure-Retarded Osmosis Power Plants: Dead Sea–Red Sea Conveyor

In this study, three pressure retarded osmosis (PRO) power plants are proposed to be built on the Red Sea–Dead Sea (RSDS) water conveyance project, to generate power from the salinity gradient between two water streams at different salt concentrations. The first two proposed plants are to be built after sea water reverse osmosis (SWRO) desalination plants, where Red Sea water and the rejected brine from SWRO plants are used as feed and draw solutions, respectively. In the third proposed plant, Red Sea water and Dead Sea water will be used. Results showed that the three proposed plants are technically feasible while the third plant is the only one that is economically feasible with a 134.5 MW capacity and a 0.056 $/KWh levelized cost of electricity (LCE). The power generated from the third PRO power plant accounts for about 24.7% of the power needed for the RSDS project that can be used to power SWRO-2 in order to reduce the electricity consumption by 49.3%. If the generated power from the proposed PRO plant is sold to the Jordanian national electricity grid at the current selling price in accordance with Jordanian prices of electricity, a saving of about 21.2% can be attained. It is found that using the power generated by the current proposed plants for desalination project purposes will significantly reduce the price of desalinated water produced from SWRO desalination plants.

Performance analysis of hybrid system of multi effect distillation and reverse osmosis for seawater desalination via modelling and simulation

The coupling of thermal (multi stage flash, MSF) and membrane processes (reverse osmosis, RO) in desalination systems has been widely presented in the literature to achieve an improvement of performance compared to an individual process. However, very little study has been made to the combined multi effect distillation (MED) and reverse osmosis (RO) processes. Therefore, this research investigates several design options of MED with thermal vapor compression (MED_TVC) coupled with RO system. To achieve this aim, detailed mathematical models for the two processes are developed, which are independently validated against the literature. Then, the integrated model is used to investigate the performance of several configurations of the MED_TVC and RO processes in the hybrid system. The performance indicators include the fresh water productivity, energy consumption, fresh water purity, and recovery ratio. Basically, the sensitivity analysis for each configuration is conducted with respect to seawater conditions and steam supply variation. Most importantly, placing the RO membrane process upstream in the hybrid system generates the overall best configuration in terms of the quantity and quality of fresh water produced. This is attributed to acquiring the best recovery ratio and lower energy consumption over a wide range of seawater salinity.

Experimental and simulation studies of two types of 5-inch scale hollow fiber membrane modules for pressure-retarded osmosis

This study experimentally and theoretically analyzed the performance of two types of large-scale hollow fiber (HF) forward osmosis (FO) modules for pressure retarded osmosis (PRO). The effects of operating conditions on the module performance of the 5-inch scale HF modules with a cross-wound HF configuration were investigated. A modified analytical model, based on the friction-concentration polarization (FCP) model, which combined the PRO theory with water flux and salt leakage, was proposed for PRO performance estimation. The theoretical results agreed within 9.7% deviation with the experimental results under all conditions. The energy efficiency of the HF PRO module was also theoretically derived. The power generation estimation for the 5-inch membrane module revealed that 10 to 15% of the energy could be recovered from the reverse osmosis seawater desalination process. However, some parts of the membrane could not be used efficiently inside the modules because of the non-optimal dimensions. Therefore, new types of modules, having shorter lengths and larger module diameters, were proposed and provided greater net energy output, as compared with the original module, due to the reduction of both the region where the water was not sufficiently permeated and the pressure drop inside the HF membrane.

Risk analysis in seawater desalination sector: a case study of Beni Saf Water Company “BWC”

In this present paper, a risk analysis approach is applied to an Algerian reverse osmosis seawater desalination plant using the MADS MOSAR method. MADS MOSAR method is a stepwise risk analysis approach containing many phases. Our work begins with analyzing a review of past accidents triggered by the Ben in Saf Water Company (BWC) seawater desalination plant locating in the Algerian coast in Ain Temouchent region and analyzing their similar seawater desalination plants (or plants that using similar and potential equipment). Then, the MADS MOSAR method will apply essentially for the macroscopic vision (Module A). The macroscopic vision corresponds to a main risk analysis. In the current case study, we were able to identify eight subsystems where sources and scenarios of hazards are identified, accident scenarios are assessed, recognized and ranked by Severity×Probability grid. We found twenty-six scenarios whose we were able to assess them in function of their and using probability x severity grid criteria. At the end of the analysis, we were able to define and suggest the most appropriate prevention and protection barriers for the potential elements in the studied seawater desalination plant, including pipelines, transformers, compressors, high pressure pumps, pressure vessels and energy recovery devices.

Technical review, evaluation and efficiency of energy recovery devices installed in the Canary Islands desalination plants

Drinking water supply through desalination processes based on reverse osmosis is a technology widely used in the Canary Islands due to its modular capacity and lower specific energy consumption compared to distillation technologies. The first energy recovery devices were based in centrifugal devices like the Francis Turbine. Later these devices were replaced by Pelton Turbines until the eighties when engineers developed positive-displacement devices called isobaric chambers for seawater reverse osmosis. Due to the importance of these devices in the reverse osmosis desalination process, this work analyzes, through several interviews and surveys, the main commercial isobaric chambers installed and their behavior based upon the experience of >50 years of the managers of several seawater reverse osmosis desalination plants, which are currently in operation in the Canary Islands. The purpose is to establish which of the energy recovery devices is the most suitable for installing in the future in medium and large capacity desalination plants. These results indicate the value of the factors studied: operational data, maintenance, troubleshooting and specific energy consumption of each device studied.

Systems-level thermodynamic and economic analysis of a seawater reverse osmosis desalination plant integrated with a combined cycle power plant

This study includes thermodynamic and economic analyses of a seawater reverse osmosis (RO) plant integrated with a small-scale combined cycle natural gas (CCGT) plant ranging from 36–71 megawatts (MW). These analyses model electricity produced by the CCGT plant as power for the RO plant or for sale to the power grid. These analyses consider the coolant flow rate, carbon intensity, and capital and operating costs of the CCGT plant. For a case where the RO plant is sized according to the rated capacity of the CCGT plant, the maximum flow rate of coolant for the CCGT plant is only 8–10% of the total rate of seawater intake for the RO plant. Thus, no additional intake capacity is needed for the CCGT plant. The carbon intensity of the CCGT plant varies from 802-885 pounds per megawatt-hour (lb/MWh) compared to an average carbon intensity of 1285 lb/MWh for the Texas power grid. The economics of the integrated facility are evaluated using a levelized cost of water (LCOW) framework, which accounts for the capital cost associated with the CCGT plant and electricity sales to the grid. Results indicate that integrating an RO plant with a CCGT plant reduces LCOW by 8–10% compared to an RO plant powered by electricity from the Texas power grid. Citation: Reimers AS, Webber ME. 2018. Systems-level thermodynamic and economic analysis of a seawater reverse osmosis desalination plant integrated with a combined cycle power plant. Texas Water Journal. 9(1):82-95. Available from: https://doi.org/10.21423/twj.v9i1.7065.

Intensification and energy minimization of seawater reverse osmosis desalination through high-pH operation: Temperature dependency and second pass implications

Operation of seawater reverse-osmosis (RO) desalination using high flux membranes at pH > 9 was shown to be an energy-efficient approach for single-pass boron removal. This operational approach was previously studied only at 25 °C, however since RO desalination is highly temperature-dependent, the current work tested the high-pH approach throughout the typical temperature range of the Mediterranean Sea. Since total dissolved solids (TDS) removal in a high-flux-membranes single-pass is limited, the effect of applying a 2nd RO pass was also examined. Finally, the process cost was assessed at varying operational conditions. Results showed 1st pass permeate TDS to be ∼440, 290 and 200 mg/l at 54% recovery-ratio and 31, 25 and 15 °C, respectively. Boron removal was adequate (i.e. <0.4 mgB/l in permeate) at pH 9.5 throughout the temperature range. However, at 31 °C antiscalant had to be added to prevent Mg(OH)2 scaling. TDS and boron concentrations in the 2nd-pass permeate met the threshold limit (30 mg/l and 0.5 mgB/l) at 90% recovery ratio. The cost of applying the single-pass alternative process was lower by about $0.03/m3 permeate than the conventional alternative, for temperatures lower than 28 °C. The addition of a second pass increased the operational cost merely by a ∼$0.03/m3, making the described two-pass process competitive.

Different boron rejection behavior in two RO membranes installed in the same full-scale SWRO desalination plant

Today, one of the main targets of seawater reverse osmosis (SWRO) membrane manufacturers is to increase boron rejection. For drinking water, the regulations in Spain are quite strict in terms of maximum boron content. The aim of this work is to propose a prediction model for average boron permeability coefficient as boric acid by evaluating the fluctuations of boron permeate concentration due to the different operating conditions of the plant under study. The SWRO desalination plant used for this study is located in Spain and has 9 trains with a production capacity of around 7200 m3 d−1 per train. Data from about 1500 operating days were considered. Operating data including pressure, conductivity, flow, temperature, pH and boron permeate concentration were collected during the study period. All racks did not have the same number of pressure vessels or operating conditions. Boron permeate concentration was between 0.5 and 2 mg L−1 for the membrane element TM820S-400 and between 0.25 and 0.75 mg L−1 for the membrane element TM820L-440. The model is based on the superposition of three exponential functions considering the influence of feed pressure, feed-brine temperature and operating time. The obtained results with the proposed model showed more adaptable to the experimental data than previous model.

Elimination of chemical products in the pre-treatment section of Las Palmas III reverse osmosis desalination plant to control fouling

The paper analyses the extrapolation of the results obtained in a pilot plant to a full-scale seawater desalination plant. A technological system was implemented in the pre-treatment line of Las Palmas III seawater reverse osmosis (RO) desalination plant with a capacity of 36,000 m3/d. This system is aimed to control membrane fouling. It consists in the non-dosing of sodium hypochlorite or another biocide to seawater in order to minimize RO membrane biofouling. The pH regulation at 6.5 controls the scaling and the 12.5 ppm dosage of FeCl3 as a coagulant maximizes the coagulation efficiency of colloidal particles and controls the fouling process.

Membrane capacitive deionisation as an alternative to the 2nd pass for seawater reverse osmosis desalination plant for bromide removal

Most Australian surface and ground waters have relatively high concentration of bromide between 400 and 8000 μg/L and even higher concentration in seawater between 60,000–78,000 μg/L. Although bromide is not regulated, even at low concentrations of 50–100 μg/L, it can lead to the formation of several types of harmful disinfection by-products (DBPs) during the disinfection process. One of the major concerns with brominated DBPs is the formation of bromate (BrO3−), a serious carcinogen that is formed when water containing a high concentration of bromide is disinfected. As a result, bromate is highly regulated in Australian water standards with the maximum concentration of 20 μg/L in the drinking water. Since seawater reverse osmosis (SWRO) desalination plays an important role in augmenting fresh water supplies in Australia, SWRO plants in Australia usually adopt 2nd pass brackish water reverse osmosis (BWRO) for effective bromide removal, which is not only energy-intensive to operate but also has higher capital cost. In this study, we evaluated the feasibility of membrane capacitive deionisation (MCDI) as one of the alternatives to the 2nd pass BWRO for effective bromide removal in a more energy efficient way.

Development and assessment of a novel solar heliostat-based multigeneration system

In this paper, a comprehensive study on thermodynamic analysis and assessment, through energy and exergy approaches, is conducted for a multigenerational solar based integrated energy system. The system proposed in this study is based on heliostat solar system integrated with steam turbine. The system is also integrated with seawater reverse osmosis desalination unit and absorption cooling system. The desalination unit operates with energy recovery through the utilization of Pelton turbine. The system produces cooling, heating, fresh water and hydrogen through electrolysis. It is furthermore designed to cover the demand of 4 MW electric power with the production of 1.25 kg/h of hydrogen and 90 kg/s of fresh water. The system advisor model software is applied on a case study for the solar heliostat optimization analysis.

Seawater desalination using pillared graphene as a novel nano-membrane in reverse osmosis process: nonequilibrium MD simulation study.

Herein, the applicability and efficiency of two types of pillared graphene nanostructures, namely, (6,6)@G and (7,7)@G, were investigated as membranes in reverse osmosis seawater desalination using extensive nonequilibrium molecular dynamics simulations. The water permeability for (6,6)@G and (7,7)@G membranes was estimated at 4.2 and 6.6 L h-1 cm-2 MPa-1, respectively. According to the results, a complete (100%) and pressure-independent salt rejection was estimated for both membranes. In addition, the mechanism of seawater desalination through the pillared graphene membranes was investigated via the density distribution profile of water molecules inside the pillar channels. Furthermore, a series of steered MD simulations were performed to construct the potential of mean force (PMF) profile of water molecules and salt ions passing through the membranes channels. The passing free energy barriers of Na+ and Cl- ions and water molecules are 0.86, 0.62, and 0.22 eV, respectively, for the (6,6)@G membrane. The corresponding quantities for the (7,7)@G membrane are 0.71, 0.44, and 0.11 eV, respectively.

A novel single-pass reverse osmosis configuration for high-purity water production and low energy consumption in seawater desalination

Seawater reverse osmosis (SWRO) desalination is required to produce high-quality water to meet stricter water standards, which could be satisfied with single-pass RO through the advancement of reverse osmosis (RO) membranes. In this study, a novel single-pass RO configuration was proposed to further improve permeate quality. Split partial single-pass (SSP) RO is a design in which the permeate from the rear RO element(s) in a pressure vessel is blended with the RO feed. This blending resulted in the dilution of the feed, leading to the production of high-quality permeate with lower energy demand. Modeling of the RO process demonstrates that SSP RO had the highest energy efficiency when the permeate from the 7th element (i.e., the last one in the single pass RO configuration) was circulated back and mixed with the feed. For typical SWRO operating conditions, SSP RO was effectively able to improve permeate quality. In fact, SSP RO produced an approximately 15% purer permeate compared to conventional single-pass RO. SSP RO was also always more energy-efficient than the two-pass RO configurations. The economic feasibility of the design was assessed further and the possibility of its practical application explored.