Unit Cost Of Water Research Articles

Optimization theory of stomatal behaviour: I. A critical evaluation of five methods of calculation

There are two principal aims in this first manuscript, first, to compare five methods for calculating the marginal unit water cost of plant carbon gain (E/A) of leaves of two Australian tropical tree species, and second, to test the hypothesis that E/A of tropical tree leaves is constant when leaf-to-air vapour pressure difference (D) varies. Few differences in the absolute values of E/A or the form of the response were found between species. However differences did exist between methods of calculation. Importantly, E/A was rarely constant with changing D. Stomatal limitations of net photosynthesis caused by a reduction in internal carbon dioxide concentration as stomatal conductance declined caused E/A to increase when D was increased. Some methods are applicable to canopy scale field measurements whilst others could only be used in laboratory settings where sufficient control of the environment is possible. The best method of calculation of E/A varied according to the criteria used to judge best. However, overall, despite the large numbers of independent data sets required, Method 1 was judged best for calculating E/A for individual leaves as, although it relies on the largest number of independently derived relationships, it has the fewest assumptions. Methods 2 and 3 were applicable to the field when a number of simplifying assumptions were made.

Optimization theory of stomatal behaviour: II. Stomatal responses of several tree species of north Australia to changes in light, soil and atmospheric water content and temperature

In a companion paper several methods of calculating the marginal unit water cost of plant carbon gain (∂E/∂A) were tested to determine whether stomata were behaving optimally in relation to regulating leaf gas exchange. In this paper one method is applied to several tropical tree species when leaf-to-air vapour pressure difference (D), photosynthetic photon flux density, leaf temperature, and atmospheric soil water availability were manipulated. The response of leaves that had expanded during the dry season were also compared to that of leaves that had expanded in the wet season. Few differences in absolute value of ∂E/∂A, or the form of the relationship, were observed between species or between seasons. In the majority of species, ∂E/∂A increased significantly as either leaf-to-air vapour pressure difference increased, at a leaf temperature of either 33°C or 38°C, or as photosynthetic photon flux density increased. In contrast, as leaf temperature increased at constant D, ∂E/∂A was generally constant. As pre-dawn water potential declined, ∂E/∂A declined, indicating increased efficiency of stomatal behaviour. The relationship between ∂E/∂A and D did not differ whether internal or ambient carbon dioxide concentration were kept constant. It is concluded that stomata are only behaving optimally over a very small range of D. If a larger range of D is used, to incorporate values that more closely reflect those experienced by tropical trees in a savanna environment, optimization is incomplete.

Microfiltration system as a pretreatment for RO units: Technical and economic assessment

Microfiltration (MF) seems to be a very attractive pretreatment technique that is increasingly being used in drinking water, seawater, and wastewater applications. Recently, it has been used as a pretreatment in reverse osmosis applications. This paper presents the results of a research project on the viability and the economics of MF as a pretreatment technique for a seawater reverse osmosis (SWRO) system. The overall performance of the MF unit indicates that the SDI of the surface seawater feed ranges between 0.26 and 3.10% with an average SDI value of 2.24. SDI of surface seawater feed is above 6.5%. Average filtrate flowrate is 3.20 m3/h. The optimal backwash interval is 10 min at variable feed flowrate. The MF unit is capable of reducing COD and BOD values and producing good quality water suitable as a feed for RO systems. The techno-economic study revealed that the total unit water costs produced by beachwell, MF and conventional surface pretreatment systems are 11.082, 12.264 and 28.153 fils/m3,† respectively. It is clear that the beachwell system is the most cost-effective among the three available techniques for seawater pretreatment. If for some reason the beachwell system is not technically feasible, then the MF system is the next most cost-effective system for seawater pretreatment. It has the added advantage of better water quality.

The analysis and performance of large-scale stand-alone solar desalination plants

The development of a simple dynamic computer model allows the performance and operational behavior investigation of a large solar seawater desalination system based on a multi-effect distillation plant and a solar pond, which is believed to be the most promising large-scale solar desalination technology known today. The whole system of dynamic behavior of the whole system is investigated, and annual water yield predictions are made during the thermal transient build-up and quasi-steady-state system operation. The effect of various design and operational parameters on system behavior are investigated. Results are offered for system sizing, design and water yield predictions, as well as system economic evaluation. Based on up-to-date construction experience, rates and market costs of components and labor, as well as updated costs of commercially available desalination plants, predictions of the unit water cost are made according to which appears to be most competitive with water cost from conventional resources in several arid and semi-arid geographical locations.

Economics of seawater desalination by reverse osmosis

Abstract The ultimate goal in the scientific study of desalting and water purification is to design a process that produces potable water at the lowest possible cost. Presently two major techniques are commercially used in different parts of the world: distillation and membrane processes. The dominant distillation process is multi-stage flash (MSF), and the main membrane process is reverse osmosis (RO). Although cost factors vary by site, the total cost of producing potable water from seawater with the RO process is usually less than thermal desalting processes. In this paper results of a study carried out in Kuwait to compare the unit cost of water produced from one-stage and two-stage hollow fiber (HF) and spiral wound (SW) seawater RO systems are presented. Results indicate that an average reduction in product water cost of about 22% could be achieved when one-stage RO is used instead of two-stage RO to produce drinking water from seawater in Kuwait. Moreover, an average of 11.84% of the capital investment cost can be saved by using a one-stage instead of a two-stage RO system. A greater reduction in product water cost is expected in the future as there is more room for improvement in the design, operation and maintenance of seawater desalination by RO technology.

Technical Aspects of Reducing Desalting Water Costs in Distillation Methods

In Kuwait, the installed capacity of desalting plants has steadily increased [from 1 migd (million imperial gallons per day) in 1953 to 254 migd in 1989] and the water consumption per capita risen (from 57 l/day in the late fifties to 272 l/day in the mid eighties). Any decrease in the desalted water unit cost thus means the saving of millions of KD. In this paper, prospects of improvements in desalination technologies by distillation processes that may affect the desalted water unit cost are discussed. These prospects include the capital cost (i.e., equipment, site, etc.) and running costs (i.e., energy, chemicals, etc.) of the main distillation systems such as multi stage flash (MSF), multi effect boiling (ME), and vapor compression (VC) systems. The effects of the design and operating parameters that have impact on the costs are outlined as well as the practical constraints imposed on these parameters. These parameters include maximum brine temperatures, type of water treatment, number of stages or effects, means of supplying energy, material selection, etc. Case studies are reviewed where non-conventional designs have been adopted with the hope of decreasing cost.

Skid mounted mobile brackish water reverse osmosis plants at different sites in Kuwait

Abstract It has been realised that the storage of water to be used during emergency cases will not be sufficient to meet water demand if emergency cases lasted for an unexpected period. This lead to the idea of having small mobile Reverse Osmosis desalination units installed at various sites in Kuwait and to serve essential communities such as hospitals and army camps. Consequently, the authors set specifications for the supply of thirteen Skid Mounted Mobile Brackish Water Reverse Osmosis units of capacity 250,000 IGPD, each. The units are identical in all aspects and utilizing low pressure membranes. This paper describes the operation, maintenance, performance and unit water cost of one of the units during one year continuous operation.

Technical aspects of reducing desalting water cost by distillation methods

In Kuwait, the installed capacity of desalting plants is continuously increasing (from 1 mgd in 1953 to 263 mgd in 1989) as well as the water consumption per capita (from 57 1/d in late fifties to 272 1/s in mid eighties). Any decrease in the desalted water unit costs means saving millions of KD to Kuwait due to the huge amounts of desalted water production. In this paper, prospects of the present and near future improvements in desalination technologies by distillation processes that may effect the desalted water unit cost are discussed. These prospects include the capital cost (i.e., equipment, site, etc.) and running costs (i.e., energy, chemicals, etc.) of the main distillation systems such as multi-stage flash (MSF), multi-effect boiling (MEB), and vapor compression (VC) systems. The effects of the design and operating parameters that have impact on the cost are outlined, as well as the practical constrains imposed on these parameters. These parameters include maximum brine temperatures, Type of water treatment, number of stages or effects, means of supplying energy, material selection, etc. Case studies are reviewed where designs, different than conventional designs, were adopted with the hope to decrease the cost.

Desalination costs in Australia: A survey of operating plants

Abstract A survey of desalination costs in Australia was conducted using data obtained from plant operators, and is reported in second quarter 1986 A$. Unit water costs range from $0.76/kL (for a precursor to deionisation for boiler feed) to $14/kL (for emergency supplies for an island resort). However, an average figure for desalination of brackish water is $3–$4/kL, and for seawater, $5–10/kL in medium-sized installations. Capital costs for brackish water plants have been correlated with plant design capacity ranging from 10 to 3400 kL/d. There is insufficient information to allow a proper comparison between reverse osmosis and electrodialysis for brackish water desalination.

R.O. design optimisation

For given seawater feed conditions a range of RO plant designs can be formulated to produce the same output. As recovery factor increases the energy consumption falls, but at a cost of installing more membranes. Optimisation between membrane and power costs will thus produce the most economic design for a given set of conditions, analogous to the optimisation normally carried out for MSF distillation plant. This paper gives examples of a family of RO plant designs of 4500m 3/day output, at varying water recoveries and feed pressures. It is shown that an optimum recovery exists for each feed pressure, and that unit water cost falls with increased pressure. Sensitivity checks are included for the effects of membrane life and energy cost.

A simple, more accurate criterion for economic evaluation of desalination projects

Economic evaluation of desalination projects is usually done by calculating a unit cost of water from the capital charges plus first year's operating costs. In this paper we show that this method can be unduly harsh on projects with high capital and low operating costs, such as solar plants, under inflationary economic conditions which are now the norm in Western societies. Standard economic evaluation methods for engineering projects are examined and it is found that none is ideal for selecting desalination processes. A new criterion — the EVAC (equal value annual cost) is introduced. It has the following advantages. it is relatively easy to calculate it is based on rigorous economic criteria and allows sound decisions to be made it can be used as the basis for pricing water. The EVAC makes allowances for cost escalation and inflation.

Optimizing design and cost of seawater reverse osmosis systems

The influence of design parameters, such as raw water temperature and total dissolved solids content (TDS), design pressure, and recovery, on total unit cost for the production of desalinated water from the Arabian Gulf in Saudi Arabia by means of reverse osmosis is presented for plant capacities ranging from 75,000 m3/d to 700,000 m3/d. It is concluded that total unit water cost is significantly influenced by raw water TDS, design pressure and design recovery. It is recommended to investigate the feasibility of operation at increased pressure. Finally, total water costs for reverse osmosis desalination are presented also as a function of salinity, with TDS levels ranging from 3000 mg/l to 55,000 mg/l.

Desalting - prospects for improvement in technology and reduction in costs

Abstract Desalting can already be considered as a reliable means of water production or water quality improvement. At the beginning of this decade, more than 2000 land-based desalting units having a combined capacity of more than 7 million cubic meters per day were operating or under construction. Many of these plants were reported to be operating reliably, demonstrating high plant availability factors. However, in most cases, the desalted water costs are still to high, especially for use in agriculture. In the past decade, desalting cost (in prevailing prices) increased, in some cases very drastically, despite improvement in technology. The main reasons for this were, obviously, the steep increase in energy costs and high rate of overall price inflation. In some cases, however, the cost of desalting was not increased in real prices, especially when using processes having relatively low specific energy consumptions. Desalting of brackish water even decreased in real prices due to impressive improvement in membrane processes, mainly reverse osmosis. For seawater desalting, recent developments and especially those now under development related to reverse osmosis membranes and efficient power recovery systems, are expected to reduce significantly the specific investment and overall operating costs. In the field of distillation, one of the more promising desalting options is that of low temperature multieffect distillation (MED) plants coupled to coal or nuclear power plants. A large prototype MED, using cheap alluminum tubing, has been recently built by Israel Desalination Engineering and is scheduled to start operation in the latter part of 1982. Various potential improvements of the MED process and optimized matching of system parameters with considered power plants will be analyzed. The two above discussed desalting options will be evaluated economically by assuming a common set of economic groundrules. The evaluation will be made for two stages of technological developments; current technology and projected technology. Recently made cost evaluations for large capacity plants, applying the two above-mentioned desalting options indicate specific investments in the range oa about $2/m 3 -year and unit water costs in the range of 60 to 70 cents/m 3 , for current or near term technology and in the range of 40 to 60 cents/m 3 for projected technology. The two more important cost factors affecting competitiveness of these two options are unit energy and membrane replacement cost. A detailed analysis of these, as well as other cost factors, along with a breakdown of the cost effectiveness of the various projected technological improvements will be given and analyzed.

Continuous Countercurrent Ion Exchange for Desalination and Tertiary Treatment of Effluents and Other Brackish Waters

A continuous countercurrent ion exchange (CCIX) process has been developed for desalination of mineralized effluents and brackish water. The process utilizes macroporous resins in a strong cation/weak anion sequence. Removal of organic matter by the anion resin results in colour and odour removal and approximately 70% reduction of the COD of humus tank effluent. No pretreatment is required and resin has been in use over the equivalent of more than two years of continuous operation without significant fouling or loss of capacity. Any required degree of desalination is attinable. The basic four-colunn system (cation load and regeneration pair and anion load and regeneration pair) of countercurrent fluidized bed multistage contactors attains greater than 80% water recovery using up to 1,0 N sulphuric acid and 0,2 N lime slurry as regenerants. Low solubility of CaSO4, in the cation waste liquid and column operating problems if high lime concentrations are used set limits on the water recovery. Calcium content of the feed water affects water recovery. New techniques using five-column systems permit byproduct recovery and/or reuse of spent regenerants and result in over 90% water recovery. The capital cost estimate for a 10 000 kℓ/day plant is R5 million while unit costs of water are 30 to 40 c/kℓ. for removal of 500 mg/ℓ TDS. Present work involves lime contacting improvements and evaluation of carbon adsorption polishing of the ion exchange product to produce potable water.

Comparison of solar RO and solar thermal desalination systems

Abstract In this paper the unit water costs from 100m3/day solar RO and solar distillation plants are compared. RO plants powered by photovoltaic cells are already available, and distillation plants operated from solar collectors are being constructed. For the size chosen and these options it is concluded that distillation is cheaper than RO for salinities above about 6,000ppm. Solar ponds can provide both thermal and electrical energy more cheaply than the above options, but they do not yet have the market penetration of the more accepted systems. If solar ponds are used then distillation is cheaper than RO only for salinities above about 10,000ppm.

OPTIMIZATION OF WATER RESOURCES FOR IRRIGATION IN EAST JORDAN1

ABSTRACTThe paper describes an approach towards optimal allocation of surface and ground water resources to three agricultural areas in the Jordan Valley under conditions of scarce water supply. The optimizing model allocates water from three main rivers, each with reservoir storage, and from two ground water sources to three irrigation regions. Productivity of irrigation water, expressed as the net present value of the regional agricultural output, but allowing for crop water deficits, is first maximized using nonlinear programming. The allocation process then adopts techniques of linear programming to determine the least cost alternative based on the unit cost of water from each resource at each destination, as it varies with time.

A review of scale control methods

Abstract The methods of scale control used in MSF evaporators, namely sodium polyphosphate, acid dosing and organic polymers are reviewed. Temperature limitations, scale control performance and plant corrosion are discussed for each method. It is shown that unit water costs reduce with increasing brine temperature and that organic polymers are now competitive with acid dosing. Recent developments in scale control for MSF and other evaporation processes are briefly discussed, including sulphate ion exchange, fluidized bed evaporators and the use of surfactants.

Guidelines for the Determination of the Feasibility of Desalting Sea Water

This article discusses the first step in preparing the capital cost approximations for a desalting facility, which is to establish the following preliminary design conditions: plant capacity in gallons per day; plant operating factor; and, economic ratio. The article provides a method for the determination of the estimated desalting facility capital cost, four cost elements that go into the determination of the unit cost of water, the elements of the fixed‐charge rate on capital investment, and other unit costs.

Economic evaluation of desalting sub-system as a part of the total water system

This paper shows that a higher unit cost for water from a desalination plant as compared with other sources could be justified. The economics of desalination is considered from the total water system of which the conversion plant may be only a component. The concept of limited planning horizon is discussed and the water system is synthesized in relation to the long term demand function. The alternative of a mix between the surface water collection systems and desalination is introduced. The traditional two alternative competition is shown to be just a special case of the general mix alternative. The optimum mix is determined on the basis of minimizing the present worth of costs in relation to demand. The variation of cost parameters with plant capacity is considered in determining the optimum capacity and life of each component. Through the use of continuous discounting (interest) and exponential approximations for the demand functions, the effects of the rate of return and rate of growth in demand on the optimum plant characteristics are shown in a direct, simple manner. This could form a basis for a consideration of the uncertainties associated with forecasted data and cost functions. With respect to the individual water supplies, capital cost allocation over the plant's life is made in such a way as to be proportional to the demand pattern. Accordingly, the concept of an equivalent marginal water pricing is formulated. This price is then minimized. The optimum life, investment and capacity are thereby determined.

Optimum Depth of Wells in Crystalline Rocksa

AbstractWater‐bearing properties of crystalline rocks are dependent on the occurrence of joints and faults and the extent of weathering. Interstitial openings caused by weathering are mostly at depths of less than 100 feet. Joints are less abundant and openings along joint planes are smaller as depth increases. Openings along fault surfaces also tend to close with depth. These geological observations which indicate a decrease in rock permeability with depth are verified by a study of well yields and water‐injection tests. Mean yields per foot of well are 0.23 to 0.30 gpm at 100 feet but only 0.013 to 0.04 gpm at 1000 feet. Mean injection rates per foot of drill hole under 100 psi pressure are 0.11 to 0.4 gpm at 100 feet but only 0.014 to 0.038 gpm at 1000 feet. Median values of both well yields and injection rates are from one‐half to one‐third of the mean values. Geologic structure is more important than rock type in determining yields and injection rates. The decrease in rock permeability with depth indicates an increase in the unit cost of water with depth. The optimum depth of a well is, therefore, determined largely by economic factors. Unless geologic factors are favorable, wells in crystalline rocks should be less than 600 feet deep. In general, domestic wells should be less than 150 to 250 feet deep.