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The effect of cell thickness and flow velocity on product water cost was investigated in order to obtain data for optimizing electrodialysis membrane stacks in water desalination. The calculations were carried out by means of a computer program; the experimental data were obtained from the determination of limiting current densities. The results indicate that a reduction of cell thickness to approximately 0.2 mm with a corresponding flow velocity of 0.13–0.17 m/s yields a cost minimum. However, this minimum cannot be identified exactly. Moreover it would be difficult to manufacture adequate sealing frames and to obtain a homogeneous flow distribution in such cells simultaneously. For industrial membrane stacks applied to water desalination, a cell thickness of 0.4–0.6 mm and a flow velocity of about 0.1 m/s seem to be the economically most reasonable design criteria.

The first seawater desalination plant by electrodialysis in the world started its operation in September, 1974 at Noshima island of Hofu city, Yamaguchi Prefecture, Japan. The capacity of the plant is 120 m3/day and the plant has been supplying fresh water from the sea for the 800 inhabitants of the island. Batchwise operation is utilized to simplify the process because of its relatively small capacity, but the operation is fully automatic to supply fresh water continuously using a storage of proper capacity. The water cost is relatively high but lower than that of conventional distillation processes of the same capacity.

An experimental RO seawater system has been in operation for two years at Eilat on the Red-Sea shore. Simplified seawater pretreatment, comprising only sand filtration and acid dosing was applied. Hollow fiber and spiral wound membranes were tested. Evaluation of pretreatment effectiveness and comparative membrane performances are reported. Investment and water cost analysis of a 4,000 m 3 /day RO seawater desalting system under various operating conditions is given. The analysis is based on the results of experimental site operation, current technology development and updated industrial quotations. The resulting water production cost from a one-stage system, adequate to produce desalted water acceptable for local drinking water standards, is approximately $ 1.1/m 3 .

There is growing concern over the quality of the nations groundwater resources. Instances of ground water contamination from organic chemicals have been reported in virtually all states. Longterm p...

This paper presents a short review of solar distillation followed by a description of conventional distillation methods and associated energy consumption. The paper then presents a system where solar energy is used to generate steam to drive a multieffect distillation plant. The system is optimized on the basis of minimum water cost . The analysis shows that enhancement of heat-transfer coefficients in the distillation section and increasing steam temperature from solar boiler result in lower water cost as well as increase the output per unit area of solar collectors. This study shows that a solar boiler producing saturated steam at 60 C in combination with an evaporator-condenser, developed and tested at this Laboratory, resulted in minimum water costs ranging from $1.40 to $3.70 per m3 for brackish water feed and $2.15 to $4.70 per m3 for seawater feed. At these conditions, the daily productivity per unit area of solar collectors ranged from 45 to 130 liters per m2. This study also shows that when the steam temperature was increased from 60 C to 88 C . the minimum water cost decreased from $2.15/m3 to $1.37/m3 for brackish water feed and from $3.60/m3 to $2.05/m3 for seawater feed. Also, at these conditions, the daily productivity per unit area of solar collector increased to 288 l/m2 for brackish water feed and to 151 l/m2 for seawater feed. These predicted values for the daily productivity are as much as seventy times the average productivity of simple solar stills at the assumed value of solar insolation.

An Idea to use a cement concrete as an evaporator shell material of a desalting plant is expected to lead to reduction of product water cost, as well as realization of durable and maintenance-free evaporator shell. p]Based upon the above idea, series of fundamental researches had been carried out on the subject such as resistivity of concrete exposed to hot sea water and hot distilled water, and changes of concrete properties exposed to an elevated temperature, which were followed by the studies on structural problems related to thermal stresses and air permeability of concrete evaporator shell. As the results of the research, the study using Test Plant with concrete evaporator shell modules was started in order to solve problems which would be encountered on the way of design, construction and operation of the plant, obtaining many Know-Hows and Experiences which lead to the design, construction and operation of the 100,000 m3/day Test Module Plant.

This paper considers distillation systems where all the plant's thermal energy requirements are provided by solar energy. Fairly small capacity plants are considered operating in remote arid regions. Such systems consist of solar collectors and thermal storage coupled to a distillation plant. Each of these aspects is considered as well as the type of control strategy to be used. Using a dynamic computer simulation model, two solar-driven systems are considered: one using flat-plate collectors and a 76°C MEE desalination plant, the other using evacuated tubular collectors and a 95°C MEE plant. Various combinations of collector area and thermal storage volume are considered, and optimal values determined for each case. For the particular example chosen (lOOm3/day, located at 23 1 2 °S) the flat-plate collector system was superior at current prices, giving an overall water cost of $5.82/m3 versus $7.34 for the second system. Both these costs are considerably less than water costs from conventional solar stills.

The current and the near-term thermal converters and the long-range fast breeders for seawater desalination are analyzed based on the fundamental principles, present technology and future development of nuclear reactors. By using the available data of light-water reactors, the trends of current and near-term thermal converters and long-range fast breeders are predicted and discussed. The unit plant cost, and the total nuclear power cost (consisting mainly of the fixed charge, the fuel cycle cost and the operating, maintenance cost) versus the cumulative and the net plant capacity (or reactor size) are respectively shown by curves. The first and the equilibrium core costs and the plant thermal efficiency versus the cumulative plant capacity are illustrated. The comparison of water cost versus net plant capacity and plant load factor for the single-purpose and the multipurpose nuclear desalting plants are also given. The feasibility and development of nuclear agro-industrial complexes and the vertical tube evaporators for desalting seawater technology are briefly discussed.

Multi-stage flash distillation and multiple effect boiling distillation are not entirely different processes, but the two ends of a continuum. The defining variable in the continuum is the rate of brine circulation relative to distillate product. The multi-stage flash “end” is characterised by morphological simplicity as compared with the MEB end which is morphologically complex. This simplicity is obtained at the cost only of increased circulation, i.e. pumping power. No water cost improvement is obtainable from the MEB system except by increasing performance ratio well beyond that achieved by multi-stage flash up to date. Multi-stage flash systems can be designed to give higher performance ratios also, and it is to this end that effort should be directed with greater acumen All argument for reversion to the MEB system is based on the assumption that in the VTE film boiling embodiment assured high heat transfer coefficients can be obtained and maintained in practice.

This study investigates economies associated with size of New England water utilities. Regression analysis techniques were applied to annual water cost and production data reported in the American Directory of Water Utilities (1968-1969). Modest economies of size in the production of water were found. Because in large communities more water is used per person, total cost increases at a slightly faster rate than population increases, but per unit costs of producing water decline. Substantial economies occurred when the number of customers was held constant and volume of water per customer increased. This study indicates possible economies when two or more of the many very small utilities combine activities to form a larger unit and by encouraging present customers to use more water.

The historical record of the cost of pumping groundwater in Arizona is examined. Measures used are the cost per acre-foot per foot of lift, the cost per acre-foot, the water cost per acre for important crops, and the total water cost per farm for representative general crop farms. Costs are presented in actual dollars and dollars adjusted by GNP implicit price deflators. Whereas pumping depths have been rising rapidly, costs per acre-foot per foot of lift have been falling, adjusted costs per acre-foot have been almost constant, and per acre costs and total farm costs relative to both total costs and total returns have fluctuated throughout the time period examined, sometimes being lower but often being higher than costs at the present time.

Dry-type cooling towers offer a solution to power plant siting problems related to thermal pollution and water supply. Dry cooling towers are being used successfully with steam electric generating plants in other countries (particularly in Europe) and in the United States. At present, only two small dry cooled electric generating units are operating in the United States but plans for a 200-mw dry cooled generating unit in Wyoming have been announced recently. The advantages of the dry cooling tower can be realized at a relatively low cost even if certain offsetting economies are not considered. All or part of the cost penalty related to dry cooling may be offset by fuel cost savings, water cost savings, transmission savings, or other savings resulting from the flexibility in plant siting permitted by the use of dry cooling systems.

Reservoir evaporation losses can be high in semiarid areas with high evaporative demand. The volume of water evaporated from a reservoir is a function of the free water surface area. In agricultural reservoirs this water surface varies depending on the volume of water stored. As reservoirs are usually relatively full of water over long periods of time, evaporation water losses are consequently high. Evaporation water savings could be achieved if a pumping policy that considered evaporation losses were developed. However, optimal pumping scheduling models proposed up to now do not take these losses into account. This paper presents a new optimal pumping scheduling model that integrates the evaporation losses from the reservoirs into the optimisation algorithm and provides the optimal pumping policy that minimises both pumping and water costs. The developed model was tested using a real irrigation water distribution system located in southeast Spain to serve as a case study. When evaporation losses were considered, water and energy savings were achieved in comparison to the optimal solution found when evaporation is not considered in the optimisation process.A sensitivity analysis of the optimal solutions to the price of water was then performed. For increasing water prices, the optimal solutions provided by the model tend to delay the pumping decisions with the aim of diminishing the evaporation losses. Although this implies a slight increase in the energy cost, it is compensated with the higher reduction in the water cost.

In desalination, similarly with other industries, the cost of the final product is one of the most important criteria that define the commercial success of a specific technology. Therefore, when new projects are planned or new technologies are proposed, the analysis of the expected costs attracts a lot of attention and is compared to (perceived) costs of state-of-the-art desalination or costs of alternative fresh water supply options. This comparison only makes sense if the cost assessment methodologies are based on the same principles and use common assumptions. This paper assesses: (i) the methodologies used to calculate the water cost; (ii) the boundary conditions and (iii) the input data and assumptions. It has been found that most papers in the literature use suitable equations and boundary conditions. Also certain elements like land costs are ignored, but in most cases this is duly acknowledged and justified. However, the quality of the input data for the hardware costs, the operating costs, and the financial parameters are not always appropriate. Guidance for the methodology, data and assumptions that should be used is provided depending on the purpose for which the cost of the desalinated water is calculated.

In the present paper, using an urban water supply and distribution system as a case study (city of Kozani, Greece), the components of the full water cost (direct-DC; environmental-EC; resource-RC) are analysed, introducing approaches for their reliable calculation. Regarding the DC, the marginal capacity cost and the necessary preconditions for its integration to the final water price are analyzed. Regarding EC, the role of non urban water users in creating EC is presented. Regarding RC, water losses are introduced as a competitive use. The role of “next more expensive solution” approach in defining ways for costs proper calculation is analyzed.

Tig. 2. Economic Repair Point as a Function of Water Cost THE losses MATTER has received of a great water-system deal of losse has received a gr at deal of attention especially during the Northeast drought of 1961-66. Then, the paucity of water made some people aware that losses from major city systems, such as New York City's, were quite large and could constitute a major potential source of "new water." Data on the extent of municipal-system losses are difficult to find. The

A reassessment of desalting plant design and product water cost based on current technology and energy and equipment costs has been made. Plant sizes in the range of 1 to 200 Mgd utilizing the multistage flash (MSF) and the vertical tube evaporator (VTE) were investigated. Process steam was assumed to be supplied by large nuclear dual-purpose plants or from fossil-fired low-pressure boilers. Plants applying the pH control method versus the threshold pretreatment method were compared. The potential benefits of applying low cost aluminum tubing in low-temperature VTE plants were also investigated.

RIASSUNTO La produzione di acqua dolce dall'acqua marina ha avuto inizio nell'era moderna con l'affermazione della propulsione navale a vapore. Il susseguente sviluppo della desalinizzazione dell'acqua marina per fornire acqua dolce sulla terraferma ha di necessita seguito lo stesso principio economico. E da attendersi che la desalinizzazione si affermi sempre piu per entrambi gli scopi. Nei primi tempi della desalinizzazione in impianti a bordo delle navi, una societa scozzese raggiunse una posizione eminente, e gran parte del contributo del Regno Unito allo sviluppo in questo settore avvenne attraverso di essa. Le prime esperienze erano tutte connesse con i sistemi di ebollizione mediante apparecchi a multiplo effetto. Notevoli anche le ricerche tendenti a impedire il formarsi di incrostazioni. Tali studi condussero alla costruzione del primo impianto di desalinizzazione sulla terraferma, ed ebbero il loro culmine con la realizzazione dei grandi impianti di Aruba e di Curacao negli anni 1955–57. In quegli stessi anni venne affermandosi il processo di evaporazione a piu stadi, che permette di ridurre drasticamente il costo dell'acqua dolce. Questo processo ha in seguito progredito rapidamente; ricerche per migliorarlo sono tuttora in corso in tutto il mondo. Oggi l'interesse e puntato, oltre che sulla distillazione, sull'elettrodialisi e su altre tecniche. L'A. discute nei particolari quanto sopra esposto, e indica le linee di sviluppo e i possibili risultati futuri. ABSTRACT The artificial production of fresh water from sea water began in the modern era with the coming of steam in marine propulsion. The subsequent development of desalination of sea water for fresh water supply on land has necessarily followed the same economic principle. We may expect to see desalination used more and more throughout the world. In the early days of ship board desalination plant, a Scottish company held quite a prominent place and much of the U. K. contribution to the development of this field was made through this industry. The early work was all concerned with the boiling system of distillation and considerable work was done to improve the thermodynamics of this by using multiple effects. There was also a substantial amount of work done on research into methods of preventing scale formation. Such knowledge led to the establishment of the first land based distillation plants. These reached their peak realisation in the installations in Aruba and Curacao, installed in the period 1955/57. These same years, however, saw the inception of the multi-stage flash process which dramatically reduced the water cost. Subsequent development of this process has been rapid and research to improve it still further is now active all over the world. Interest is active not only on distillation but on electrodialysis and other possible techniques. The paper covers in detail most of the matters summarised above, with indications of the new lines of work and the possible future outcomes. RESUMe La production de l'eau douce a partir de l'eau de mer est commencee dans l' âge moderne par l'emploi de la vapeur dans la propulsion des navires. La subsequente diffusion du dessalage de l'eau de mer pour fournir l'eau douce aux populations de la terre a suivi, par necessite, le mcme critere economique. Il faut s'attendre a ce que le dessalage s'affirme de plus en plus pour ces deux necessites. Aux premiers temps du dessalage effectue dans les installations a bord des navires, une societe ecossaise atteint une situation eminente et c'est pour la plupart grâce a elle que le Royaume Uni contribua au developpement de ce secteur. Les premieres experiences avaient ete effectuees toutes par les systemes d'ebullition a L'Aide d'appareils a effet multiple. A remarquer aussi les recherches pour empecher la formation d'incrustations. Ces etudes eurent pour resultat la construction de la premiere installation terrestre de dessalage et aboutirent a la realisation des grandes installations d'Aruba et de Curacao en 1955–57. Pendant ces mcmes annees s'affirma le processus d'evaporation a plusieurs etages, qui permet de reduire nettement le cout de l'eau douce. Ce processus a fait ensuite de progres considerables; dans le monde entier on est encore en train d'effectuer des recherches pour L'Ameliorer. L'interet se porte, maintenant, sur la distillation aussi bien que sur l'electrodialyse et sur d'autres techniques. L'A. examine en detail ce qu'il a expose ci-dessus et indique les nouveaux criteres de travail ainsi que les possibles futurs resultats.

Rising water cost and drought-caused local shortage caused these authors to seek more economical strategies in the lab.