Large-scale Seawater Reverse Osmosis Research Articles

Optimize and analyze a large-scale grid-tied solar PV-powered SWRO system for sustainable water-energy nexus

The lack of clean water and access to energy are two major obstacles to global sustainable systems. The development of solar photovoltaic (PV) technology gained the attention of water desalination projects due to its cost decline, carbon-free emission, and the on-site energy production. However, studies on in-depth analysis of the performance of these systems remain rare. This study performs a comprehensive a design optimization and seven-factor analysis (energy, exergy, economic, environmental, energoeconomic, exergoeconomic, enviroeconomic - 7E) of a grid-tied PV system powering a large-scale seawater reverse osmosis (SWRO) plant. First, an optimal design model is developed based on real hourly measured data for the SWRO load demand and renewable resources, while considering net energy metering mechanism. The objective function is delineated to diminish the energy cost of the system, concomitant with the imposition of operational constraints. Second, an analytical model is established to perform exergetic calculations for the optimal design. Third, a sensitivity analysis is conducted to show how the model parameters affect the system design and costs. The results show that the optimal system relies on a 4.25 MW solar PV array and a 3.125 MW grid-tied inverter. This configuration reduces the levelized cost of energy by 48.3 % and carbon emissions by 50 % compared to a grid-only system. The implementation of net-metering has also maximized the designed system's revenues to 263,834 $/year. Further, the optimally designed system achieves a lower levelized cost of water (0.2217 $/m3), minimal capacity shortage, and negligible unmet load ratios (0.048 %) despite grid outages. From the exergetic assessment, the proposed system has a high exergy efficiency (9.3 %) which can be achieved despite the high value of the exergy loss. Moreover, the energoeconomic and exergoeconomic indicators have recorded tiny values (3.35E-5 kWh/$ and 0.0311 kWh/$, respectively), which are considered a desired outcome. Notably, a profit of 4285.4$ is achieved through the sale of carbon emissions reduction. The sensitivity analysis revealed an increase in the system's total cost of 4.91 % and 9.36 % and the system's energy cost of 4.91 % and 8.7 % if the energy purchase price raised by 10 % and 20 %, respectively. Also, it indicates that a fall in the electricity sellback rate of 10 % would remarkably raise the system's energy cost by 47.3 %. Finally, reducing the PV-Inverter costs by 15 % would drop the system's net present and energy costs by 51.4 % and 60 %, respectively. Overall, the insights from this study have the potential to expedite the realization of sustainable development goals 6, 7, and 13, particularly in developing nations abundant in solar energy resources.

Energy and water without carbon: Integrated desalination and nuclear power at Diablo Canyon

A seawater reverse osmosis (SWRO) desalination plant collocated with an existing nuclear plant would have low electricity costs, could share the power plant’s seawater intake and outfall, and would have zero carbon footprint during operation. Unlike thermal desalination technologies, electrically-driven SWRO is ideal for retrofitting existing power plants because the turbines and condensers would not need expensive modifications. Here, we evaluate the techno-economic feasibility of collocating a large-scale SWRO plant with an existing nuclear power plant, specifically the 2.2 GWe Diablo Canyon Nuclear Power Plant on California’s central coast. The seawater that cools the nuclear plant’s condensers provides the feed water for desalination. The desalination brine is diluted with the remaining condenser coolant before being discharged to the ocean. A brushed-screen intake structure, serving both the nuclear power plant and the desalination plant, can comply with strict California regulations protecting marine organisms. This coproduction arrangement has a significant cost advantage relative to a stand-alone desalination plant. The levelized cost of water (LCOW) ranges from US$0.77 to US$0.98 per m3 of fresh water, with water distribution to offtakers adding US$0.02 to US$0.21 per m3 over 20–185 km. In comparison, California’s largest desalination plant, in Carlsbad, has an LCOW of about US$1.84 per m3. These cost savings result from reduced power costs (about US$0.054 per kWh) and from sharing some expensive infrastructure. Further, nuclear electricity allows a Carlsbad-size SWRO to avoid 47 kt/y of CO2 emissions relative to grid electricity. Examination of substantially larger desalination plants introduces additional considerations. This study is the first to show that collocated SWRO and nuclear power are strongly coupled and have a significant economic advantage over seawater desalination at other sites. These benefits should apply to dozens of existing nuclear power plants worldwide.

Design strategies for reducing energy and total costs for large-scale seawater reverse osmosis plants

One of the main obstacles limiting seawater reverse osmosis (SWRO) from becoming a more widespread solution to water shortages is the overall capital and operational costs, partially driven by energy consumption required for the SWRO process. Since its inception, however, the power requirement for SWRO has decreased dramatically through numerous factors, including improved RO membrane performance, the introduction of energy recovery systems, and improved design practices and efficiency. While many of these solutions relate to technological advances, membrane system design can be optimised during the design stage and maximise total cost savings of using SWRO. Improving design practice of SWRO to reduce power consumption requires a thorough analysis of all components, such as operating conditions, recovery, system flux, and membrane model selection. This paper presents essential design considerations that impact energy use and strategies for maximising total cost savings for SWRO plants.

Determination of optimal design factors and operating conditions in a large-scale seawater reverse osmosis desalination plant

A large-scale seawater reverse osmosis (SWRO) plant was designed with a capacity of 10 million imperial gallon per day (MIGD) and to optimize design factors and operating conditions of the plant, various evaluations were undertaken. These involved pretreatment investigations, split partial simulations, evaluation of the final water quality with respect to production capacity, and a performance comparison with other SWRO plants using the normalized specific energy consumption (SEC). As a result, the turbidity and silt density index values of the pretreatment permeates were not affected by the productivity of the plant during the operation period. Additionally, the optimum split partial ratio of the RO membranes was determined to be 4.5:5.5 which satisfied the final produced water quality and energy consumption requirements. Based on the split partial ratio, the total dissolved solids (61–280 mg/L) and boron (0.1–0.9 mg/L) concentrations of the final permeate satisfied the Korean standards at all capacities (5.7, 8.0, 10 MIGD). In particular, the total SEC of the 10 MIGD train was estimated as 3.66 kWh/m3, which is greatly lower compared to that of other SWRO plants with similar capacities. Thus, these specific performance evaluations will be useful in determining the optimal design factors and operating conditions for other large-scale SWRO plants.

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.

Characterization of microbial communities in water and biofilms along a large scale SWRO desalination facility: Site-specific prerequisite for biofouling treatments

Biofouling impacts seawater reverse osmosis (SWRO) desalination plants by hindering module performance, increasing energetic demands, and incurring further costs. Here we investigated the spatial–temporal dynamics of microbial communities along the feedwater, pretreatment, and reverse osmosis stages of a large-scale SWRO desalination facility. While the composition of water-based microbial communities varied seasonally, the composition of biofilm microbial communities clustered by locations. Proteobacteria dominated throughout the water and biofilm communities while other dominant phyla varied seasonally and spatially. The microbial community composition significantly differed along the pathway locations of feedwater, rapid sand filtration (RSF), cartridge filters (CF), and the reverse osmosis (RO) membranes. Biofilms on the RSF and CF were composed of more diverse microbial populations than RO biofilms as determined by the effective number of species. Biofilms that developed along the treatment pathway (CF) served as inocula enhancing biofouling downstream on the RO membranes. Subsequently, we believe that prior to the development of advanced antibiofouling treatments for the desalination industries, the site-specific microbial community of feedwater, pretreatment and RO biofouling should be characterized. Site specific identification of these communities will enable optimization of pretreatment and cleaning procedures and can ultimately reduce chemical usage and incurred costs.

Optimal operations for large-scale seawater reverse osmosis networks

Optimal operation of large-scale seawater reverse osmosis (SWRO) systems, which include multiple RO plants and storage tanks, are studied to reduce the energy cost; and at the same an effective computing method was introduced for the purpose of real time optimization. With well developed models of the RO process and storage tanks based on the first principle, the optimal operation problem is subsequently formulated in the form of differential-algebraic optimization problems (DAOPs). Simultaneous collocation method was used to transform the problem into a large-scale nonlinear programming problem, and then IPOPT solver, combined with an efficient initial-value and finite-element meshing technique, was used for fast solution. Then the optimal operation problem with different variable parameters that significantly affect the performance and the energy saving of the SWRO system were investigated through case studies. Computational results show that the optimal operation problem under different conditions can be solved with high efficiency and stability, and significant energy-saving potential can be obtained through the optimal operation proposed in this paper.

Seawater desalination as an option to alleviate water scarcity in South Africa: the need for a strategic approach to planning and environmental decision-making

In the last decade, seawater reverse osmosis (SWRO) has come to be seen by policy-makers as a novel technology that will significantly advance water security in South African coastal regions. Water purveyors, from the private sector, local/district municipalities and provincial authorities, are undertaking studies to explore the feasibility of SWRO to meet growing demand and relieve mounting pressure on current bulk water supply infrastructure. With this in mind, it is suggested that national strategic planning should be introduced to present the opportunities and constraints of the desalination option within the national water and energy policy. In absence of this, piece-meal decisions will be made at local authority levels and the construction of SWRO plants will be determined by regional circumstances (e.g. drought) as opposed to national water policy agenda. This paper explores the value of such a strategy by considering the drivers of SWRO in South Africa, the risk of unplanned large-scale SWRO implementation (with a focus on environmental impacts) and the initial steps that could be taken toward a Strategic Environmental Assessment for SWRO in South Africa.

Modular pumps bring efficiencies

Positive displacement, water lubricated axial piston (AP) pump technology can be used in a modular arrangement to replace less efficient, centrifugal (CF) pumps that are currently the dominant solution for high pressure pumping used in large scale seawater reverse osmosis (SWRO) systems. A preliminary review of the modular positive displacement axial piston pump system reveals this new concept is not only a cost effective alternative to traditional centrifugal pump systems, but may have other advantages during the SWRO facility operating period.

Technical review and evaluation of the economics of water desalination: Current and future challenges for better water supply sustainability

Desalination capacity has rapidly increased in the last decade because of the increase in water demand and a significant reduction in desalination cost as a result of significant technological advances, especially in the reverse osmosis process. The cost of desalinated seawater has fallen below US$0.50/m3 for a large scale seawater reverse osmosis plant at a specific location and conditions while in other locations the cost is 50% higher (US$1.00/m3) for a similar facility. In addition to capital and operating costs, other parameters such as local incentives or subsidies may also contribute to the large difference in desalted water cost between regions and facilities. Plant suppliers and consultants have their own cost calculation methodologies, but they are confidential and provide water costs with different accuracies. The few existing costing methodologies and software packages such as WTCost© and DEEP provide an estimated cost with different accuracies and their applications are limited to specific conditions. Most of the available cost estimation tools are of the black box type, which provide few details concerning the parameters and methodologies applied for local conditions. Many desalination plants built recently have greater desalinated water delivery costs caused by special circumstances, such as plant remediation or upgrades, local variation in energy costs, and site-specific issues in raw materials costs (e.g., tariffs and transportation). Therefore, the availability of a more transparent and unique methodology for estimating the cost will help in selecting an appropriate desalination technology suitable for specific locations with consideration of all the parameters influencing the cost. A techno-economic evaluation and review of the costing aspects and the main parameters influencing the total water cost produced by different desalination technologies are herein presented in detail. Some recent developments, such as the increase of unit capacity, improvements in process design and materials, and the use of hybrid systems have contributed to cost reduction as well as reduction in energy consumption. The development of new and emerging low-energy desalination technologies, such as adsorption desalination, will have an impact on cost variation estimation in the future.

Desalination plants in Australia, review and facts

Australia is the driest continent on earth and despite this the installed desalination capacity is still around 1% of the total world's desalination capacity. This paper reviews the main seawater issues considered in every desalination project—the history, the present situation and the future of desalination in Australia, the suitability of applying reverse osmosis (RO) and the project details of two desalination plants (Sydney and Perth). Ocean currents, seawater temperature and salinity are signifi cant indicators in the assessment of the feasibility of desalination as they aff ect the production costs, the maintenance frequency and the quality of the product water. Seawater reverse osmosis (SWRO) is the only type of desalination technology currently used or proposed for future large-scale desalination plants in Australia. Every capital city except Darwin has considered building at least one desalination plant as a means of providing water security after several years of unprecedented drought that has signifi cantly reduced dam storage levels. Perth was the fi rst major city to use desalinated water for drinking water supply and by early 2009 Sydney will be the second city. Thirteen other large-scale SWRO plants are being planned or proposed at several locations for the purpose of supplying drinking water.

Utilization of waste heat from a flue gases up-stream gas scrubbing system

A thermal seawater desalination plant which utilizes waste heat from flue gases upstream, flue gas desulphurization (FGD), is discussed. This type of “low-grade” heat is suitable for low-temperature desalination technologies such as multi-effect distillation (MED) technology. Two different alternatives for using the heat is analyzed and compared. In these schemes, about 8,500–10,000 m3/d of high-quality water (∼10 mg/l TDS) may be produced from one 575 MW generating unit. Moreover, a great amount of water is saved due to reduction in flue gas temperature and therefore reduction in water evaporation in the flue gas scrubber. An economics evaluation of the alternatives is presented. The water cost obtained is in the range of 53–62 US cent/m3 and depends on the MED and gas cooler capital costs, unit capacity factor and required rate of return. The obtained costs are comparable to water cost obtained from state-of-the-art, large-scale sea-water reverse osmosis (SWRO) plants even without taking into account the higher water quality.