Operation Of Desalination Plants Research Articles

The potential of laser scanning cytometry for early warning of algal blooms in desalination plant feedwater

When algal blooms (such as red tide) occur, early detection of increased algal growth in intake water offers desalination plant operators advanced warning of severe fouling and provides the necessary time for preventative measures. Monitoring basic water quality measurements such as turbidity, silt density index (SDI), dissolved oxygen, and bulk fluorescence can approximate algal activity; however, these measurements lack the resolution needed to accurately track growth throughout all phases of a bloom event. This study investigates the use of a laser scanning cytometer (LSC) that detects algal cells over a wide range of concentrations (50–150,000 cells/ml), and characterizes cell shape, size, and distribution parameters through fluorescence signal imaging. Water samples are filtered to collect algae on a 0.2-μm membrane surface. Sample volume is variable so cells can be concentrated. The membrane surface is scanned with a 635-nm diode laser and the signal is processed to generate a cell count and distribution image. LSC performance was comparable to fluorescence microscopy and flow cytometry over a range of concentrations that may be encountered during a bloom event. The applicability of LSC was demonstrated using laboratory-grown cultures and seawater samples taken during a bloom event off of the coast of Long Beach, CA.

Operation of desalination plants using renewable energies and hybrid control

This paper presents a control system for the operation of desalination plants powered by locally generated renewable energy. To cope with the variability of the water demands and the available energy, the amount of water produced must be manipulated optimally. This is carried out by regulating a variable speed pump, using hybrid predictive control, which takes into account the operational limits of both the pump and the process. The operation is complex because the scheduling of the cleaning operations and the optimization of the energy consumption must be performed simultaneously to the control of the plant, fulfilling a set of additional constraints. The paper uses a continuous reformulation of the problem in order to simplify the optimization process. Simulations of a specific plant show that an optimal operation reduces the extra energy consumption, and makes it possible to supply the variable water demand.

Effect of the Discharge Water which Mixed Sewage Disposal Water with Seawater Desalting Treated Sewage for Bottom Sediment and Hypoxic Water Mass

For every time in summer season, hypoxic water mass has formed at the inner part of Hakata Bay. Field observation study has carried out at the inner part of Hakata Bay since 2004 with the particular aim of tracking the movement of hypoxic water mass. Hypoxic water masses form the end of June to September on this area because the consumption of oxygen in bottom water layers exceeds the re-supply of oxygen from the atmosphere. Under such hypoxic conditions, the seawater desalination plant has begun to use in 2005. After seawater desalination plant operation starting, hypoxic water mass tends to improve. In this research, the authors show the following result. After seawater desalination plant has begun to operate, the hypoxia around the mixed discharge water outlet tends to be improved.

Seawater intake and partial pre-treatment with Neodren - results from investigation and long-term operation

In the last few years the efforts to improve operation and maintenance of seawater intake systems and of the pre-treatment of seawater for desalination plants have been enforced, especially for those designed on the basis of the membrane process reverse osmosis (RO). Driving forces have been the increasing importance of seawater desalination with RO, the need for the reduction of related costs, and the minimization of the impact of the operation related side effects on the environment. This concerns, e.g., the discharge of water resulting from rinsing and cleaning processes, that are also influenced by agents used in the pre-treatment. Thereby as one very important aspect it has to be considered, that the intake and the pre-treatment of seawater have to be adapted to the specific conditions at the construction site of each plant. These can differ however in a wide range. Beside the influences determining the rawwater quality, also items like the geological situation, environmental aspects and details related with infrastructure or logistic are usually different and have to be considered consequently during design, construction and operation of a desalination plant. A successful possibility to reduce these efforts has shown to be the seawater intake and partial pre-treatment system Neodren, that allows for a reliable and long-term operation of desalination plants with nearly no need for chemicals, under certain circumstances even without them. The system is based on porous drains that have been installed with a specially developed horizontal directional drilling technology in about 4–7 m depth in the stratum below the seabed. This is acting as a natural filter and helps to avoid completely usual problems at seawater intakes, like influences on the marine habitat or weather induced contamination peeks. Even if the first system is in trouble-free operation since 1996, and in June 2008 nine systems with a total capacity of about 382,000 m3 of Neodren-filtrate per day have been installed and are successfully in operation, further investigation is carried out by Catalana de Perforacions and cooperation partners, to take advantage of all benefits of these systems. As one option has been identified to operate them in combination with ultrafiltration. That would allow for increasing the productivity of the RO units, or, if compared to an operation with conventional pre-treatment, for a reduction of the necessary membrane area for the production of the same capacity respectively. Related results from investigation are presented together with an overview of Neodren systems with long-term operation, that confirm the economical and ecological sustainability of the Neodren technology, and details of a new installation.

Residential Water Scarcity in Cyprus: Impact of Climate Change and Policy Options

This paper presents an assessment of the cost of water scarcity in Cyprus, today and in the next 20 years, taking into account the effect of projected climate change in the region. It focuses on the residential sector, accounting also for tourism and industry. Using a simple demand function, total scarcity costs in Cyprus are computed for the period 2010–2030, and three scenarios of future water demand are presented. The central estimate shows that the present value of total costs due to water shortages will amount to 72 million Euros (at 2009 prices), and, if future water demand increases a little faster, these costs may reach 200 million Euros. Using forecasts of regional climate models, costs are found to be about 20% higher in a “climate change” scenario. Compared to the loss of consumer surplus due to water shortages, desalination is found to be a costly solution, even if environmental damage costs from the operation of desalination plants are not accounted for. Finally, dynamic constrained optimization is employed and shows that efficient residential water prices should include a scarcity price of about 40 Eurocents per cubic meter at 2009 prices; this would constitute a 30–100% increase in current prices faced by residential consumers. Reductions in rainfall due to climate change would raise this price by another 2-3 Eurocents. Such a pricing policy would provide a clear long-term signal to consumers and firms and could substantially contribute to a sustainable use of water resources in the island.

Experience gained through the implementation and operation of a solar humidification—dehumidification desalination plant

The proposed work aims at evaluating the experience gained by the design, implementation and operation of a pilot solar thermal desalination plant installed in the Geroskipou municipality, Cyprus, based on the humidification-dehumidification technology. The design of the plant enables the direct use of the heat produced by the solar thermal system in periods of low water demand. The working principle and the technological solutions adopted for the specific application are presented. The various technical problems encountered during the installation and operation of the unit are discussed. Finally, the critical parameters which affect the performance of the desalination unit and the techno-economical sustainability of the installation as a whole are analysed.

Ripening of granular media filters for pretreatment of seawater in membrane desalination

The successful operation of a seawater reverse osmosis desalination plant depends greatly on the performance of the pretreatment step. The start-up of a pretreatment filtration process usually begins with a dynamic part called ripening, during which the filter media increases its adsorption ability and improves the removal of foulants from the seawater. In that period (typically lasting 30–60 min, depending on the system's conditions) the effluent often does not meet the quality requirements of the RO membranes and must often be disposed of. An observation and analysis of the ripening phenomena was performed using lab scale acrylic filter columns containing granular activated carbon. The seawater originated from the Yellow Sea in Korea and an inline coagulation was performed prior to filtration using an optimal dose of FeCl3 based on a jar test. The turbidity, total suspended solids concentration and dissolved organic carbon were measured before and after filtration with the goal of assessing the filtration performance. The filter media, which was cleaned and dried before filtration showed distinct ripening characteristics. The measurements were then used for parameter identification of a typical filtration model. Based on the fitted model one can predict the optimal filter depth that would reduce the waste stream production of the plant.

Prospects of operation of MSF desalination plants at high TBT and low antiscalant dosing rate

Control of scale formation on heat transfer surfaces is one of the basic problems in thermal desalination processes. There are several commercial antiscalants available in the market mostly derived from condensed polyphosphates, polyelectrolytes and organophosphonates. A comprehensive study was carried out for direct performances in comparison of three of the most widely used antiscalants. They include a maleic acid based copolymer antiscalant #1, a maleic acid based copolymer antiscalant #2 and a phosphonate based antiscalant #3. The comparative study was performed in a MSF pilot plant under harsh operating conditions. For each of the three antiscalants, the MSF pilot plant was operated at a TBT of 119 °C, a dose rate of 1 ppm and a brine recycle concentration factor of 1.9 for one month. A baseline test was performed under the same TBT and concentration factor without the use of an antiscalant. Test results reveal that antiscalants were quite effective in suppressing scale formation under the selected operating conditions. It is recommended to reconsider current scale control operating conditions of commercial MSF plants especially with regards to optimization of antiscalant dose rate and brine concentration factor.

State of the reverse osmosis membrane of sea water corso plant desalination (Algiers)

Seawater reverse osmosis (SWRO) desalination is being increasingly emphasized as a strategy for conservation of limited resources of freshwater. Although desalination has been developed for the last few decades, the SWRO operation is still affected by membrane fouling. The membrane fouling of SWRO has a significant impact on operation of desalination plants. We follow the evolution of the permeate conductivity during three months of the sea water Corso (Algiers) plant desalination. The purpose of this work is to conduct an autopsy of fouled membranes in seawater using the scanning electron microscopy (SEM) coupled by an analysis EDX. This membrane shows a change of the surface morphology, which justifies the abrupt increase in the conductivity of the permeate in May 2006. In order to identify the nature of the fouling deposit, we analysed this deposit by Xrays diffraction (XRD).

Artificial neural network model for optimizing operation of a seawater reverse osmosis desalination plant

An artificial neural network (ANN) was developed to predict the performance of a seawater reverse osmosis (SWRO) desalination plant, and was then applied to the simulation of feed water temperature. The model consists of five input parameters (i.e., feed temperature, feed total dissolved solids (TDS), trans-membrane pressure (TMP), feed flow rate, and time) and two output parameters (i.e., permeate TDS and flow rate). Then, the one-year operation data ( n = 200) from the Fujairah SWRO plant was divided into three data sets (i.e., training, validation, and test data set) to develop the ANN model. The trained ANN model was subsequently found to produce good agreement between the observed and simulated data (TDS: R 2 = 0.96; flow rate: R 2 = 0.75) in the test data set. The results of this study show that the variation of the feed water temperature and TMP was found to significantly affect both the permeate TDS and flow rate. From subsequent simulations with various temperature controls, it is further suggested that the permeate TDS can be reduced using a linear increase control (from 27.5 to 29.5°C) for the feed temperature in an SWRO hybrid system with multi-stage flash (MSF) distillation, such as the Fujairah plant.

Development of a package model for process simulation and cost estimation of seawater reverse osmosis desalination plant

Seawater reverse osmosis (SWRO) desalination is rising as an alternative solution for the water shortage problem which is more severe than before. In this study, a package of process models was developed and tested by four-year SWRO plant operation data obtained from Fujairah in UAE, as a tool not only for simulating the performance of SWRO desalination process but for estimating the total profits of the plant operation. The simulation results based on the developed process models were reasonably satisfied to predict the SWRO desalination plant performance in terms of permeate water concentration and flow rate. And the results of cost estimation show a possibility that the models can successfully predict total annual profits (TAP) within the order of magnitude of USD/year, according to operating date, feed water concentration, and permeate water condition. Consequently, the developed package model is applicable to support design criteria and efficient operation of SWRO desalination plant as references.

Innovation Addresses Environmental Issues at Sydney Desalination Plant

As water storage levels declined in Sydney, Australia, during 2003 and 2004, the New South Wales government imposed water restrictions and directed government agencies to conduct feasibility studies on new water supplies. Sydney Water commenced a desalination feasibility and planning study in 2005. By 2006, all planning and environmental approvals had been obtained. To confirm negligible impacts from operating a desalination plant, Sydney Water conducted an extensive marine monitoring program. Information required for the design phase was completed in mid-2007 and used to develop a blueprint that served as a proof of concept and hastened the procurement process. Information gathered included seawater-quality and current monitoring, physical modeling of diffusers, and ecotoxicity testing. Current baseline studies began in early 2007 and will continue until the plant is commissioned next year. The studies include water-salinity monitoring, reef habitat surveys, and organism recruitment studies. The studies will be repeated during the project's post-commissioning phase for three years. When collected, both datasets will be used to verify the environmental assessment's prediction of negligible effects on the marine environment resulting from desalination plant operation.

Experimental biological effects assessment associated with on-shore brine discharge from the creation of gas storage caverns

Most of the studies on biological and ecological effects associated with brine discharge into the marine environment are related to the operation of desalination plants, for the production of freshwater. In this study we analysed the biological effects of a brine effluent from a completely different source, produced from the lixiviation of rock salt caves, for the creation of natural gas storage caverns. Lethal and sub-lethal endpoints following exposure to the brine were studied in a range of macrofauna species characteristic of the soft and hard bottom habitats in the vicinity of the discharge area, namely the isopod Eurydice pulchra, the annelids Sabellaria alveolata and Ophelia radiata, the sea-urchin Paracentrotus lividus and the bivalve Mytilus galloprovincialis. In a first series of experiments, brine, with salinity above 300, was diluted in distilled water to a salinity value close to that of the seawater in the discharge area (salinity 36) and, surprisingly, none of the exposed species was able to survive or develop into viable larvae. A second series of experiments exposed the species to brine diluted with seawater, simulating more realistic discharge circumstances. All the tested species at all the measured endpoints (adult survival, larval abnormal development, sperm fertilization success) showed negative biological effects in brine solutes always at a lower salinity than that of a salinity control obtained with concentrated seawater. The sub-lethal experiments with larval development of P. lividus, S. alveolata and M. galloprovincialis, and the fertilization success of P. lividus gave EC 50 values for the brine solute with salinity in the range of 40.9–43.5, whereas the EC 50 values for the concentrated seawater were in the range of salinity 44.2–49.0. It is hypothesised that differences in the ionic composition of the brine cause the inability of the species to tolerate the exposure to brine.

Jellyfish blooms:Crambionella orsini(Scyphozoa: Rhizostomeae) in the Gulf of Oman, Iran, 2002–2003

In 2002, a jellyfish bloom occurred throughout the Gulf of Oman and the Persian Gulf causing decreased catch in artisanal and industrial fisheries, damage to fishing gear, interrupted operation of desalination plants, and damage to the seawater cooling systems of coastal power plants. The cause and source of the bloom and the species of medusa were unknown. Here, the temporal and spatial distribution of the medusa are described using data from incidental catches in Iranian fisheries surveys, and morphological and molecular evidence are used to identify the medusa asCrambionella orsini(Vanhöffen). This species is endemic to the western Indian Ocean and adjacent basins which dismisses species introduction as the cause of this bloom. Furthermore, because the bloom was geographically widespread, it probably was not caused by local coastal degradation. Although human activities with large-scale effects cannot be ruled out, large-scale oceanographic or ecosystem conditions, perhaps part of natural climate cycles, that yielded moderate sea surface temperatures (in terms of the annual mean monthly anomaly for each year since 1982) were the most likely causes of the bloom of this endemic jellyfish.

Seawater intake and pre-treatment/brine discharge — environmental issues

In some cases the only remaining option to satisfy the increasing demand for potable water in good quality for the growing population, is the desalination of seawater, being used more and more the membrane process reverse osmosis. But whereas for the design and the manufacturing of the desalination units itself meanwhile are available well known and approved technical solutions, the intake and the pre-treatment of the seawater, as well as, the discharge of the brine have to be adapted to the specific conditions at the construction site of each plant. These conditions can differ in a wide range, as beside the influences determining the raw water quality, also items like the geological situation and details related with infrastructure or logistic are usually very different and have to be considered consequently during design, construction and operation of a desalination plant. The same applies for the aspects concerning the environment, that are becoming more and more important due to changing local legislation, increasing public awareness, growing construction density at coastal areas and also due to findings regarding the impact on the marine environment based on long-term operation of desalination plants. Thereby one of the most important prerequisites for reliable long-term successful operation of reverse osmosis seawater desalination plants is a consistent high quality pre-treatment of the feed water. One possibility to fulfil this requirement is the use of directed drilled horizontal drains below the seabed as seawater intake and partial pretreatment system according to the patented Neodren technology. With these horizontal drains, that are based on an improved horizontal directional drilling (HDD) technology and high efficient patented filtering devices, the raw and fine screening, as well as, the conventional filtration of seawater and the dosage of different pre-treatment agents will not be necessary. Due to extremely low filtering velocities, this is achieved without impingement and entrainment of aquatic organism. This system, developed by Catalana de Perforacions with the first unit in operation since 1996, can be operated in sandy and karstic seabeds as ecological and economical alternative for conventional open seawater intake systems, and has even advantages in comparison with indirect seawater intake systems like beach well installations. Due to the modular design there is no limitation regarding the production of pre-filtered water. Also based on the HDD technology have been developed systems for a controlled brine discharge that consider the environmental conditions on site. Details of these different intake and discharge systems and their environmental impact will be compared.

Criteria and procedure for selecting a site for a desalination plant

Desalination plant site selection is very vital for the design, financing construction and operation of desalination plants under a public private partnership or a Turnkey basis. The site, comprised of inland and offshore parts, (i) must be located in a place where access and interconnections to the power supply grid, (or independent power production) and to the water supply networks are technically and economically feasible, (ii) the area extent and shape (size and geometry) must be the appropriate so that the marine intake head structures, the marine pipelines, the inland pit the seawater pumping station, the inland pipelines, the main facility structures, the post treatment system, the product delivery sub-system, and the power supply system (IPP or national grid substation) are adequately accommodated and optimally located so that civil, electrical, piping interconnections and other works costs are minimized, (iii) be suitably located in a marine environment where adequate quantity of feed water with a reasonable good, uniform and steady quality of feed seawater is abstracted at a reasonable cost, (iv) be at a location where the brine, backwash wastewater and other wastes are disposed without environmental adverse effects, (v) geologically and topographically are suitable for the construction and erection of the various structures at reasonable costs, (vi) environmental, town planning and rural planning regulations, law requirements and restrictions are met, (vii) the desalination plant shall have the social acceptance of the neighboring communities and other authorities and finally (viii) the local taxes are not prohibitive and the existing infrastructure shall make easier and cheaper the project implementation. This paper presents and analyses the site needs to accommodate a desalination plant, the need for the early site selection, the identification of the concerned partners, the composition and set up of the special committee, the terms of reference to the special committee, the criteria that should be taken into consideration, the time period, and the procedure to be followed for the selection of the most appropriate site. The selection of a technically, economically, environmentally and socially accepted site shall reduce the risks involved in the design, construction, the operation and maintenance of the project and generally decrease the unit cost of water.

Process modelling in desalination plant operations

Operation of desalination process is sometimes a difficult task, especially when the plant is getting older. Process engineers and operators are required to follow-up any changes or variations in process parameters either in control room or on-site measurements. Undetectable deviation and/or malfunctioning in any of measurement devices could occur specially during long-time successful operation without major shutdown for the entire plant or when the process is part of very complex integrated processes in an industrial site. This deviation, inaccurate-reading or malfunctioning values can be due to un-calibrated devices (i.e. flow-meters) or fouling of measurement devices (i.e. thermo-couples). Practically, process modelling is a useful tool that can assure and confirm that the process measurements parameters are accurate. Incorrect balancing of mass and/or energy can be detected easily as well as the productivity of the plant. In this paper, multi stage flash (MSF) desalination plant was illustrated and evaluated. Malfunction of measurement device showed the plant was producing distillate more than what was really measured or received by down stream processes. Excel spreadsheets was developed and utilized for process modelling and confirming the results.

A new approach to meet the growing demand of professional training for the operating and management staff of desalination plants

For the expected installation and operation of additional seawater desalination plants, manpower is needed. Besides the financing and the manufacturing of these plants, the training of the future staff is a big challenge. It is assumed that in the MENA region each year more than 1000 people will have to be trained. The present and future problem at seawater desalination plants, i.e. the lack of experienced personnel, is also a lack of instructors. There are already existing institutions and facilities in various countries carrying out well-organized training programs at site. In addition, there are many excellent short courses and workshops organized by organisations like EDS or MEDRC — nevertheless, the crucial question remains whether these structures are strong enough to meet the growing demand for professional training in the future. When talking about training programs, the question of how to finance these measurements emerges directly. The solution can be found in an improvement of the availability of the plants. A higher availability resulting in a higher fresh water production rate could be obtained by well-trained staff able to react in a proper way to any disturbances or unstable operation modes of the plant. The so-called “Twinning-Model” could be a suitable approach to meet the demand for professional training. A central training facility called TFEU (based in Europe and affiliated to an existing university or a technical school) is one of the twins and plays the part as developer of training programs (curricula), as instructor for the trainers and as trainer for advanced and simulator courses. Following the curricula, additional experts from other universities or companies are integrated in the team. After an initial phase needed for the training of the trainers, the local “twin” called TFLO is responsible for the fundamental and main training program. A board comprised of participants from all parties involved (i.e. TFEU and TFLO, the manufacturers as well as the operators) surveys the curricula and examination procedures.

Experience feedback on operation of low-temperature vacuum evaporation-based desalination plant integrated with CIRUS

CIRUS is a 40 MWth, heavy water-moderated, light water-cooled and natural uranium-fuelled research reactor located at Trombay, Mumbai. The reactor has been in operation since 1960 with an average availability factor of about 70% for about three decades. During the early 1990s, the reactor exhibited signs of ageing. It was refurbished and put back into operation at high power in 2003. Bhabha Atomic Research Centre (BARC) has been engaged in R&D activities related to desalination. Using low-temperature vacuum evaporation technology, the centre has been studying the possibility of using the waste heat of nuclear reactors for seawater desalination. Based on this know-how, a 30 cu m per day (30 tonnes/day) pilot plant has been designed. With the aim of demonstrating the utilisation of waste heat from research reactor, it was decided to integrate the unit to CIRUS during refurbishing outage of the reactor. The work involved the design, installation and commissioning of a set-up to transfer heat from the primary coolant of CIRUS to the desalination unit through an intermediate demineralised water circuit. The unit has been operated at its rated capacity and its performance has been satisfactory. The product water has been utilised to augment the demineralised water inventory of the primary coolant system. This paper highlights the experience gained during the installation, commissioning and operation of the desalination unit.

Review and evaluation of desalination cost and costing methodologies

Recently, desalination is becoming a viable alternative for supplying potable water due to new developments in desalination technologies. At present, the cost of desalinated water is about US$0.5/m³ by RO and US$ 1.0/m³ by thermal processes. But these costs are location dependent. Thus the selection of an appropriate desalination technology for any location needs a reliable and accurate costing methodology. Better costing methodologies are also required for optimal process design and economical operation of desalination plants. There are so many costing methodologies reported in the literature with varying accuracy and details. Most of the publicly available costing methodologies are either black-box type with less details of costing methodology, or use thumb rules that do not sufficiently account local conditions. Therefore, there is a need to develop a more reliable and accurate costing methodology for public use. In this paper, desalinated water costs and costing methodologies with respect to accuracy and reliability are reviewed.