Operation Of Desalination Plants Research Articles

Comparative economic and environmental assessments of centralised and decentralised seawater desalination options

This study presents comparative life cycle assessments (LCAs) and levelised cost (LC) analyses of desalination supply systems, integrated with a spatial–temporal model at three geographical scales: a centralised scenario and two alternative decentralised scenarios. For the centralised scenario we focused on a proposed 320,000m3/day SWRO desalination plant to support future urban expansion in the northern corridor of Perth, Western Australia. The alternative, decentralised scenarios each integrate several medium sized plants into the same geographical water demand area as the centralised scenario and also produce 320,000m3/day in total. Results indicate that environmental impacts would be ~20% lower and LC 7% to 18% lower for the decentralised scenarios than for the centralised scenario. Contribution analysis revealed that, for the centralised scenario, although economies of scale resulted in lower environmental impacts from the desalination plant construction and operation phases, these savings were outweighed by the environmental impacts associated with the construction and operation of the water transfer mains required to connect the large plant to the network. Perth water stakeholders and policy makers can use our results to inform development decisions, and the proposed LCA method can be implemented in other metropolitan areas for desalination planning.

Characteristics of membrane fouling by consecutive chemical cleaning in pressurized ultrafiltration as pre-treatment of seawater desalination

Chemical cleaning of membranes is one of the most important strategies in pressurized hollow fiber ultrafiltration (UF) as a pre-treatment for seawater desalination. Various physical cleaning strategies such as backwashing, aeration and air-scrubbing or chemically enhanced backwashing (CEB) have been investigated in order to remove foulants from the UF membrane. However, the limitation in their cleaning effects being found during long-term operation leads to the need of cleaning in place (CIP) for the recovery of membrane performance. In this study, we used oxalic acid and sodium hypochlorite as chemical cleaning agents. The cleaning in series of oxalic acid–sodium hypochlorite–oxalic acid showed the optimal cleaning efficiency and was applied for the consecutive chemical cleaning. The recovery efficiency of the CIP after first, second, third and fourth cleanings was 96.8%, 95.8%, 98.3% and 99.9%, respectively. It was almost fully recovered to the previous recovered value. However, membrane surface structure was deformed by contact with chemical cleaning agents during cleaning time, because, hydrophilic inorganic foulants are still adhered on the membrane surface even after several cleanings although hydrophobic organic foulants were removed easily by chemical cleaning. An improved CIP strategy should be developed to remove hydrophilic foulants for long-term operation of desalination plants.

Operation of Cap Djinet desalination plant and dilution of brine with power station cooling water

The aim of this work was to describe the operation of the desalination unit at the thermal power plant of Cap Djinet (Eastern Algeria) and the management and characteristics of the brine. The desalination unit at the thermal power plant of Cap Djinet (Eastern Algeria) operates a multi-stage flash distillation (MSF). The desalinated water passes through a demineralization step to obtain water with characteristics according to a boiler feed water at high pressure. During rejection, the brine is subjected to dilution with cooling water. This causes a decrease in the brine water salinity from 70 to 40 g/l and conductivity of 85 to 56 ms/cm which is equal to the conductivity of seawater. For other parameters, we found the same results as seawater based on the results of various analyses, we can say that the rejection of brine diluted station Cap Djinet is similar to seawater as probably it does not affect the receiving marine environment.

Fault Detection and Isolation in a Spiral-Wound Reverse Osmosis (RO) Desalination Plant

Sensor fault detection and isolation (SFDI) approaches, based on support vector regression (SVR) plant sensor models and self-organizing-map (SOM) analysis, were investigated for application to reverse osmosis (RO) desalination plant operation. SFDI-SVR and SFDI-SOM were assessed using operational data from a small spiral-wound RO pilot plant and synthetic faulty data generated as perturbations relative to normal plant operational data. SFDI-SVR was achieved without false negative (FN) detections for sensor deviations of ≳|10%| and FN detections of, at the most, ≲|5%|, and for sensor deviations of ≳|4%| at sensor fault detection (FD) thresholds of up to ∼|4%|. False positive (FP) detections were almost invariant, with respect to sensor FD, being ≲|5%| for sensor deviations of ≳|5%|. Corrections of faulty sensor readings were within SVR model accuracy (AARE < 1%) for SFDI-SVR and ≲|5%| for SFDI-SOM. Although SFDI-SOM has lower detection accuracy, it requires a single overall plant model (or SOM), while providing pictorial representation of plant operation and depiction of faulty operational trajectories.

Ocean current and temperature analysis using satellite data for the effective operation of SWRO desalination plant in Gijang-gun, Busan, South Korea

The salt concentration of seawater is a significantly sensitive factor in the seawater reverse osmosis desalination plant that applies different pressures in freshwater production, depending on the salinity of the seawater. For the efficient operation of the plant, it needs to be grounded on investigations and analyses of seawater salt concentration and water temperature distribution and change. The conventional research methods, however, have temporal and spatial limitations. This research uses the latest satellite data to analyze the flows and the seasonal temperature distributions of ocean currents that affect mostly the changes in the seawater salt concentration in the neighboring waters of the seawater desalination plant that is being built in Gijang-gun, Busan, South Korea. The results of this research showed that the ocean current in the neighboring waters of Gijang-gun, Busan had a relatively slow velocity (average: 0.05 m/s) but formed very comprehensive flow shapes as the warm and cold currents met and that the degree of the salinity change was significant because the temperatures of the sea surface differed considerably in summer unlike in the other seasons.

Thermal and economic analyses of solar desalination system with evacuated tube collectors

Conventional seawater desalination technology could solve the problem of fresh water shortage, but consumes a large amount of fossil fuel and causes the environmental problems such as global warming and acid rain. On account of this, solar desalination is one of the promising methods. The thermal and economic performance on solar desalination system with evacuated tube collectors and low temperature multi-effect distillation is researched in this paper. Mathematical and economic models are established based on mass and energy conservation, which conclude evacuated tube collector model, heat storage tank model, flash tank model, multi-effect distillation model and electrical heating and cooling model. Taking actual operation into account, the influence of the heating steam temperature of the first effect and the effect number of multi-effect distillation system on system performance is analyzed. The cost constitution of solar desalination system with evacuated tube collectors is shown, and the proportion of the cost of evacuated tube collector is the largest. The water cost is given out to appreciate the economic performance of the solar desalination system. The conclusions are helpful to the design and operation of solar desalination plant.

The research on thermal and economic performance of solar desalination system with salinity-gradient solar pond

Conventional seawater desalination technology could solve the problem of fresh water shortage, but consumes a large amount of fossil fuel and causes the environmental problems such as global warming, acid rain, etc. On account of this, solar desalination is one of the promising methods. Mathematical and economic models of solar desalination system with salinity-gradient solar pond (SP) which both supplies the energy and store energy in system are established. A Visual Basic and A MATLAB computer programs of solar-powered low temperature multi-effect distillation (LT-MED) processes are developed. It is researched that the effect of the temperature of stream entering into the external heat exchanger and the temperature of stream returning to SP on thermal and economic performance of solar desalination system. The conclusions are helpful to the design and operation of solar desalination plant.

Optimizing desalinated sea water blending with other sources to meet magnesium requirements for potable and irrigation waters

Sea water desalination provides fresh water that typically lacks minerals essential to human health and to agricultural productivity. Thus the rising proportion of desalinated sea water consumed by both the domestic and agricultural sectors constitutes a public health risk. Research on low-magnesium water irrigation showed that crops developed magnesium deficiency symptoms that could lead to plant death, and tomato yields were reduced by 10–15%. The World Health Organization (WHO) reported on a relationship between sudden cardiac death rates and magnesium intake deficits. An optimization model, developed and tested to provide recommendations for Water Distribution System (WDS) quality control in terms of meeting optimal water quality requirements, was run in computational experiments based on an actual regional WDS. The expected magnesium deficit due to the operation of a large Sea Water Desalination Plant (SWDP) was simulated, and an optimal operation policy, in which remineralization at the SWDP was combined with blending desalinated and natural water to achieve the required quality, was generated. The effects of remineralization costs and WDS physical layout on the optimal policy were examined by sensitivity analysis. As part of the sensitivity blending natural and desalinated water near the treatment plants will be feasible up to 16.2 US cents/m3, considering all expenses. Additional chemical injection was used to meet quality criteria when blending was not feasible.

A new, energy-efficient approach for boron removal from SWRO plants

A different approach for the operation of seawater reverse osmosis desalination plants, in which the boron concentration in the product water should not exceed 0.3 mgB/L, was recently introduced. The new approach is based on strong acid (either H2SO4 or HCl) dosage to the feed seawater to attain pH ∼ 4.3, followed by almost complete CO2 stripping and subsequently strong base addition to pH 9.0–9.25. At this high pH range, a high B removal efficiency can be attained even by the new generation of ultra-low energy (high-flux) membranes. This paper addresses the energy saving potential stemming from the elimination or size reduction of the 2nd reverse osmosis (RO) pass and from the use of high-flux elements, both made possible by the new approach. Additionally, total dissolved solids removal from the 1st RO pass permeate can be obtained by operating a smaller, more energy efficient, 2nd RO pass.

Renewable desalination: a methodology for cost comparison

The increasing water demand and the impacts of climate change call for the construction of a large number of new desalination capacities, causing—besides environmental impacts—a relevant amount of additional power consumption. Consequently, new power plants need to be installed and operated as base load plants in order to supply power continuously to the desalination units. As fossil fuel prices are characterized by high volatility and a clear trend upwards, the use of renewable energies allows for saving fossil fuels and therewith reducing risks related to energy price escalation along the whole desalination life cycle. However, the fluctuant nature of renewable energies conflicts with the—ideally—continuous operation of desalination plants. In contrast to technologies such as photovoltaic (PV) and wind power, which are prone to fluctuating and intermittent power generation, concentrating solar power (CSP) is able to supply firm capacity on demand and can be fully integrated into conventional power utilities. On the other hand, CSP is currently considered to be more expensive than other renewable energy technologies. This work highlights the key importance of comparing technology options with equal quality of supply in order to obtain resilient results. Within this work, a representative site in the Middle East and North Africa Region has been analyzed by two different methodologies in order to demonstrate the potential large difference of results. The first method assumes that any variations of renewable energy supply can be compensated by the electricity grid, while the second method assumes that the addition of load to the electricity grid will require the addition of an equivalent firm power supply capacity. Hourly solar and wind data of a typical meteorological year have been used as inputs for a techno-economic simulation. Different options for CSP solar field layout, thermal energy storage, PV, and wind installed capacity, are analyzed and compared in terms of power and water cost for reverse osmosis and multieffect distillation plants.

Optimum operation of desalination plant to minimize power consumption and water shortage risks in Okinawa, Japan

ABSTRACT Okinawa Island is located in the southern region of Japan and has a population of 1.22 million. Okinawa Prefectural Enterprise Bureau (OPEB) supplies 410,000 m3/d of water to 24 municipalities. Although OPEB uses multiple water resources including dam reservoirs and groundwater, increased water demand resulted in occasional water shortages until a seawater desalination plant (40,000 m3/d) started operations in 1997. In this study, a model was developed to simulate the water supply system of Okinawa Island using precipitation and OPEB operational data from 2009 to evaluate the role of the desalination plant in reducing risks associated with drought and power consumption of the plant. The simulation results indicate that without the desalination plant, the dam reservoir storage falls below 50% for 70 days, whereas with the desalination plant, storage remains above 50%. If the plant was operated at full capacity, the dam reservoir storage increased by 17.2% after 1 year of simulation time. However, ...

Optimization of energy costs for SWRO desalination plants

The global expansion of seawater desalination and the associated excessive energy consumption have serious economic and environmental consequences. Various technological and operational approaches have been applied in an attempt to mitigate these impacts by improving the desalination process and by increasing plant efficiency, with the emphasis on reduction of the energy consumption and costs. In this study, a Linear Programming (LP) model was developed to optimize operation of a large Seawater Reverse Osmosis desalination plant (140 MLD). The objective was to minimize energy costs, using the extra hourly installed capacity of the plant and the advantages offered by the power pricing system, based on time and peak load demand (Time Load Tariff [TLT]). For annual production of 45 million m3 of desalinated water (88% of the maximum possible production capacity), a reduction of 15% of the electricity bill, equal to a saving of about US$ 2 million, can be achieved reflecting a weighted average cost of 7.66 ¢/kWh vs. a normative weighted average tariff of 8.95 ¢/kWh. The results indicate that the LP model could serve as an effective decision-making tool of desalination plants that are dependent on the supply of power from the national grid, where the price of energy is based on TLT. The model can assist in the daily operation and maintenance of the plant. It can also serve as a planning tool during the design stage. The model can be used to optimize the trade-off between plant capacity and its related investment cost to the energy expenses. It can be used to compare a smaller capacity plant having a lower investment cost but higher annual energy costs, to a plant with extended capacity having a higher investment cost but lower annual energy costs.

Overview of existing water and energy policies in the MENA region and potential policy approaches to overcome the existing barriers to desalination using renewable energies

Most countries in the Middle East & North Africa (MENA) region currently face water scarcity and rising water demand. In order to respond to these challenges, many MENA countries proceed to the use of desalination. As desalination processes are highly energy-intensive, the use of conventional energy for the operation of desalination plants contributes to climate change through greenhouse gas emissions, with negative impacts on the water cycle. The use of renewable energy sources to supply desalination plants with electricity can be a more sustainable and environmentally friendlier option to bridge the water demand gap. The present paper outlines the main barriers to desalination using renewable energies (referred to in short as ‘renewable energy desalination’, RED) in most MENA countries, gives an overview of main features of the water and energy policies in the MENA region, and compares them to the framework conditions in Australia or Spain. Supportive policy approaches to overcome the existing barriers and to promote RED are highlighted. The paper advocates the importance of adopting a more consistent legal framework to foster the deployment of RED and thereby reduce the effects of climate change and water scarcity.

Nuclear desalination: Practical measures to prevent pathways of contamination

Seawater desalination using nuclear energy is an inevitable option for the production of potable water. It is a reliable and economical way to alleviate global concerns on climate change and water scarcity issues. However, producing potable water from a co-located nuclear power plant raises some concerns regarding pathways of contamination of radioactivity to the final water. This paper examines all possible contamination pathways and analyses the preventive measures that are used both in design and operation of nuclear desalination plants. Innovative measures such as the use of heat pipes are also presented. Experience with the commissioned systems and practices related to the quality of the product water for 250 demonstrated reactor-years, shows no examples of contamination.

Seawater Desalination Plant Optimization Based on Membrane Replacement and Cleaning

Operating expenses (OPEX) for a seawater reverse osmosis (SWRO) desalination plant result primarily from energy use, membrane cleaning, and maintenance, all of which are influenced by RO membrane performance. Desalination plant operators can reduce energy consumption and increase water output by cleaning membranes more frequently or replacing aging RO membranes; however, doing so increases cleaning and maintenance costs. In addition, such actions may not improve overall OPEX of the desalination plant. This article evaluates how membrane element replacement and cleaning strategies affect OPEX generally and the Perth Seawater Desalination Plant specifically.

The Effects of Gold Coast Desalination Plant Operations on the Marine Environment

Australia's Gold Coast Desalination Plant (GCDP) provides a climate-independent source of water to the South East Queensland Water Grid. Potential environmental impacts were identified and addressed in the plant's design and construction, with particular focus on marine intake and brine discharge. Pursuant to regulatory approval and good environmental practices, various marine-monitoring programs were implemented to assess marine impacts and benefits resulting from the operation of marine seawater intake and brine outfall systems. The monitoring programs— receiving environment monitoring program, entrained organism monitoring program, and monitoring of diffuser and intake structures—are the focus of this article. Based on the results, it has been concluded that the plant's features and operational procedures ensure minimal environmental impact on biological parameters.

Laboratory desalination experiments with some algal toxins

Over the last several decades, countries throughout the world have experienced an escalating and worrisome trend in the incidence of harmful algal blooms (HABs). A concern is that highly potent algal toxins might be retained in the treated water, posing a threat to human health. Seawater contaminated with saxitoxins, domoic acid, okadaic acid, and brevetoxins was desalinated using small (<100mL capacity) reverse osmosis and distillation equipment. Analyses of desalinated water samples indicated efficient removal of the four toxins to greater than 99%, except brevetoxins for which some carry-over was observed during distillation. Hypochlorite concentrations of 4ppm or higher were sufficient to react with all of the saxitoxins, domoic acid and okadaic acid in the samples that contained initial toxin concentrations up to 1250ngmL−1. Brevetoxins appeared to be unaffected in experiments in which the toxins were exposed to up to 30ppm hypochlorite in seawater at 35°C for 60min. These results and their implications in terms of desalination plant design and operation are discussed.

A novel approach for SWRO desalination plants operation, comprising single pass boron removal and reuse of CO2 in the post treatment step

A different approach is presented for the operation of seawater RO desalination plants in which the boron concentration in the product water should not exceed 0.3mgB/l. The approach is based on strong acid (either H2SO4 or HCl) dosage to the feed water to attain pH∼4.3, followed by CO2 stripping and subsequently strong base addition to pH 9.00–9.25. At this high pH range, a high B removal efficiency is attained, and since the water is practically devoid of carbonate species, no CaCO3(s) scaling takes place, and pH elevation is limited by Mg(OH)2(s) precipitation, expected only at pH>9.45. The approach enables operation in the absence of antiscalants. Furthermore, CO2 stripping is effected in stripping towers in two steps: the high CO2(aq) concentration is first stripped by vacuum-operated stripping towers and the CO2-rich air is used for dissolution of calcite in the post treatment stage. The remaining CO2 mass is stripped to the atmosphere using blower-assisted stripping towers. This paper aims at introducing the new concept and providing “proof of concept”. The paper addresses experimental and theoretical aspects of the proposed process, as well as engineering and economic evaluation. The proposed approach is shown to be both technically feasible and cost effective, as compared with conventional boron removal alternatives.

A joint power and desalination plant for Sinai and the Gaza Strip

Desalination can be a cost-effective way to produce fresh water and possibly electricity. The Gaza Strip has had a complex hydro-political situation for many years. Gaza is bordered by the Mediterranean sea in the west, by Israel to the north and east and by Egypt in the south. Water and electricity consumption in the Gaza Strip is expected to increase in the future due to the increasing population. In this paper, a solution for Sinai and the Gaza Strip is suggested involving the building of a joint power and desalination plant, located in Egypt close to the border with Gaza. The suggested joint project would increase drinking water supply by 500,000 m3/d and the power supply by 500 MW, of which two thirds is suggested to be used in Gaza and one third in Sinai. The present lack of electricity and water in Gaza could be erased by such a project. But Egypt will probably gain more: more water and electricity for the future development of Sinai and Gaza; a significant value will be added to the sale of Egyptian natural gas; more employment opportunities for Sinai people; the domestic market for operation and maintenance of desalination plants can be boosted by the suggested project; Egypt may naturally and peacefully increase its cooperation with and presence in Gaza, which should lead to increased security. This type of project could also get international support and can be a role-model for cooperation and trust-building between neighbours.

Long term membrane process and performance in Ashkelon Seawater Reverse Osmosis Desalination Plant

In this paper the operation of Ashkelon SWRO desalination plant since it was started five years ago is reviewed. This particular installation is key for the history of seawater desalination by reverse osmosis not only because of its permeate production capacity of 100 Million m3/a (later increased to 133 Million m3/a) but also due to the low cost of water attained (50 US $/m3) when it was started up. The performance assessment made to each one of the four stages in Ashkelon indicates that no major variation in terms of energy consumption, yearly production and permeate quality has occurred since the beginning of the operation. The evaluation has been made using normalization tools together with a direct comparison between the operating values collected at the start-up and the current performance. These findings are especially remarkable if we take into consideration that the big majority of the reverse osmosis elements installed in Ashkelon and still in operation are currently more than five years old.