Innovative Inland Brine Disposal Options

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INNOVATIVE INLAND BRINE DISPOSAL OPTIONS

Shamia Hoque, Graduate Research Assistant, Department of Civil, Architectural and Environmental Engineering, Drexel University, 3141 Chestnut Street, Philadelphia, PA 19104, U.S.A.; [email protected] Terry Alexander, Undergraduate Research Assistant, Department of Civil, Architectural and Environmental Engineering, Drexel University, 3141 Chestnut Street, Philadelphia, PA 19104, U.S.A.; [email protected] Patrick L. Gurian, Assistant Professor, Department of Civil, Architectural and Environmental Engineering, Drexel University, 3141 Chestnut Street, Philadelphia, PA 19104, U.S.A.; [email protected] ABSTRACT

Growing demand, concerns over droughts, over-allocation of surface water resources, and depletion of freshwater aquifers have all made desalination of brackish groundwater an increasingly important option for inland communities. However, these communities must find a means to dispose of the concentrated saline residual waste stream in an environmentally sound manner. Evaporation ponds are one of the primary options, but this technology has a large land requirement, which makes it costly. A concern for large facilities is that this technology is one of the few treatment methods that offers decreasing returns to scale due to increasing boundary layer resistance for larger ponds.

This study evaluated a number of innovative options for improving the performance of evaporation ponds. Viable methods identified from the literature are: 1) fabric evaporators, 2) wetted boundary layer breakers, 3) salt-tolerant plants, and 4) droplet spraying. Two cost models are developed, one for boundary layer breakers and one for droplet spraying. Incremental costs and incremental evaporation enhancements are compared with site-specific cost information for a wastewater treatment facility in California's Central Valley. Results indicate that both boundary layer breakers and spray technologies are cost-effective compared to a simple expansion of the pond area. Boundary layer breakers appear to be more cost-effective per gallon incremental capacity but have a lower evaporation enhancement capacity compared to droplet spraying (24% enhancement vs. 35% enhancement). For a new facility, an example calculation with preliminary cost information indicates that spray evaporation is more cost-effective because of avoided pond excavation and lining costs. Boundary layer breakers are preferred as a retrofit to an existing facility, if they provide sufficient additional capacity to avoid the need for an expansion of the pond.

Keywords: desalination, residuals, evaporation pond 1 INTRODUCTION Evaporation ponds are lined detention basins, into which wastewater is discharged and held to allow evaporation to decrease the water’s volume. Since the cost of disposing of wastewater depends on volume and not on concentration, it is more cost effective to

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dispose off a small amount of extremely saline water than a large amount of slightly saline water. Evaporation ponds can be a cost-effective alternative for dewatering compared to other methods, which require energy and maintenance. They are used mainly in semi-arid regions where the cost of land is low. Evaporation ponds have some disadvantages. These include the expense of using an impervious liner to avoid seepage of saline waters into the aquifer and the necessity of large quantities of land when high levels of evaporation are required (1). Research has hence focused on finding methods which will increase the evaporation rate. Enhancing the evaporation rate would result in reducing the size of the evaporation ponds and decreasing costs for both the liner and the land (2). The objective of this report is to review and evaluate available alternatives to enhance evaporation from these ponds. The first section of this report provides a detailed look at the methods available in the literature for increasing evaporation. In the next section, the currently available methods are reviewed and compared. Recommendations and conclusions follow. 2 LITERATURE REVIEW Several researchers have looked at different methods to enhance evaporation rates (3-5). Kingdon (3) explored the concept of adding foreign gas molecules to weaken hydrogen bonds. The author suggested that the hydrogen bonds of water could be weakened by attaching foreign molecules to the surface. This would result in an increase of the evaporation rate. The gases examined included helium, nitrogen, butane, and oxygen. Butane worked best. Barthakur (4) studied a method using air ions in an electric field to evaporate water faster. He discovered that the electric wind created at a high voltage (5250V) produced turbulence in the water resulting in a four-fold increase of the evaporation rates. Other researchers have looked at the possibility of adding dye to maximize the utilization of solar energy (6-8). A colored solution would absorb more solar energy, increasing temperature, and resulting in lower surface tension, higher saturation vapor pressure, and subsequently increased evaporation rate (2). The researchers observed an increase in evaporation rate through the addition of methylene blue dye (7) and recommended the addition of three and a half grains of dye per cubic foot of brine (8). Other possible methods to enhance evaporation include spraying the brine, increasing turbulence in the pond, passing the brine over inclined rough surfaces and creating airflow over the pond (2). Among the various alternatives, the following four options were identified for a more detailed review: 1. Wind-aided intensified evaporation (WAIV) 2. Wetted floating fins 3. Salt tolerant plants 4. Spray method These methods are summarized in Table 1 and are discussed in more detail in the following sections. 2.1 Wind-aided intensified evaporation (WAIV) Wind-aided intensified evaporation (WAIV) is a method in which water is pumped onto fabrics to provide additional surface area for evaporation (1). The authors (1) had two different configurations for the WAIV experiments. The first was a roof top set up


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where different evaporation surfaces were tested. The surfaces tested were nonwoven geotextile and woven netting fabrics. The fabrics were constantly wetted by a supply of water from the head tank or feed pipe. The fabrics had an exposed length of ~5.74 ft (1.75m) per length of fabric running from head tank to collection tank. There are several methods of implementing WAIV. All versions required pumping water to an elevated storage tank. The methods differed in the way water from the head tank reached the strip of fabric. In some cases it was through capillary action, in other cases gravity was used. The gravity method proved to be more efficient. From the elevated tanks, water would run down the fabric at a constant rate. The test areas were in the range of 2-6.5 ft2. The roof testing was done on brine with total dissolved solids (TDS) of 16-18 g/L and was supersaturated with respect to calcium. The second set up involved a larger evaporation surface (107-430 ft2). The surface was stretched over a vertical height of ~5ft and arranged in a rectangular array. In this method, it is essential to prevent the materials from drying out. In one case during a two-month study one of the fabrics dried out due to lack of feed water. In spite of rewetting, the material’s efficiency had fallen significantly. The authors suggested (1) that it was because the salts had deposited in the fabric and hence impeded the water flow. Every two months the material would have to be rinsed with water and if necessary citric acid (1). This would help reduce the amount of residual salts on the fabric and keep the material from drying out. The study concluded that woven netting fabric is a better choice over the nonwoven geotextile fabric because the woven netting had significantly less salt deposits on its surface. This method was tested against an open pan evaporation pond and it was shown that the procedure can increase the amount of evaporation by 50% on a given area of fabric compared to an open water surface (1). Overall a 13-fold increase in performance for a given land area is reported as it is possible to fit a large fabric surface area within a relatively small footprint. Also, the most severe test was done using water with a total dissolved solids (TDS) level of 18g/L. Concentrations of salt higher than those tested would produce more deposits on the fabric which would possibly increase the frequency and the cost of maintenance. 2.2 Wetted floating fins Another potential method is using floating aluminum fins to enhance the surface area available for evaporation. This does not require pumping and uses the absorbent properties of the material to elevate the water vertically. The floating fins would provide an additional area of exchange and also act as a boundary layer breaker (9). Experiments were conducted in the laboratory in a wind tunnel of cross-section 50cm by 50cm. The water container used was 100cm×19.5cm×10cm and was thermally insulated (9). An electric heater was used to heat the water from the bottom. The experiments looked at both parallel and perpendicular orientation of fins to the wind. Three parallel fins and five perpendicular fins were used. The dimensions of the parallel and perpendicular fins were 88cm×3.8cm×0.32cm and 19.5cm×3.8cm×0.32cm respectively. The fins were covered with a cotton cloth to keep them permanently wet through the wicking action of the cotton (9). Temperature, humidity and wind speed were also measured.


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The author (9) defined a coefficient of effective additional fin area, ε . Its value was determined through experiments and mathematical analysis. The value of ε determines the equivalent free surface area of a unit of fin area added. For example, for a fin area of a , the additional equivalent free surface area would be aε .The study showed that in heated water (45-65oC) for perpendicular fins and at wind speeds of 5m/s the value of

0.76ε = while parallel fins have an 0.16ε = . Hence, the fins would have to be placed perpendicular to the wind flow to obtain maximum advantage. When the water temperature was <20oC for perpendicular fins, ε varied between 0.26 for wind speeds of 1m/s to 1.2 for wind speeds of 5m/s. A 24% enhancement of evaporation could be obtained in uncontrolled ambient conditions for a value of 0.6 forε (9). The effectiveness of the fins depended on fin orientation, relative humidity and wind speed. The author also determined that the most effective spacing between each fin would be five times the height of the fin. 2.3 Salt tolerant plants Although it would require more maintenance compared to the first two, enhancing evaporation with salt tolerant plants is another alternative. The plants that could be used are a group of plants called “halophytes”, which are tolerant to high levels of salts. By utilizing the natural processes of transpiration (evaporation through leaf stomata) in plants, the effective surface area in which evaporation occurs is increased. A study on salt tolerant plants concluded that saltwater cordgrass (Spartina alterniflora) and great bulrush (Scirpus validus) were acceptable to treat water which contained greater than 100g/L of total dissolved solids and about 60 g/L of chloride (10). Other species of halophytes tested were: coastal dropseed (Sporobolus virginicus), perennial glasswort (Salicornia virginica), sawgrass (Cladium jamaicenese), and vermillion cordgrass (Spartina alterniflora var. vermillion). For dissolved solids of roughly 3% or less, several-fold increases in evaporation rate are possible. Winter weather would decrease the evapotranspiration rates; however this would still be higher than the open surface evaporation rates (10). The extra maintenance cost could be offset by potential sales of the harvested halophytes. The water evaporated and the salt covered leaves of the plants would have to be tested for the specific facility. In the previous study, tests on the salt covered leaves did not find significant levels of toxic contaminants, and hence cattle were allowed to graze on the halophytes (10). The economics of the process would have to be investigated before any application, but it is reported to be economically feasible (7).

2.4 Spray method Spraying water droplets into the air was among the different alternatives discussed in the literature for enhancing evaporation from evaporation ponds. The increase of evaporation is due to the increased area of the air water interface (5). The spray method could be implemented by constructing a sprinkler system on the pond or by installing a cooling tower on the evaporation pond. 2.4.1 Sprinkler system To determine the enhancement of evaporation due to a sprinkler system or a spray pond an experiment was developed involving the construction of a pond of 172ft×112ft (52m×34m) and fitted with an array of 24 nozzles at the center of the pond (5). The


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nozzles sprayed at a pressure of 10psig and at a flow rate of 8gpm/nozzle. A low pressure was maintained to reduce any spray drift. In the month of June in Wyoming, an evaporation rate increase of 0.34 inches was observed. Modifications in height, nozzle angle and flow rate of sprinklers yielded an overall evaporation rate increase of ~ 35%. Evaporation losses by a single droplet during flight range from 2-15%, with smaller droplets losing more because of their higher surface area to mass ratio (11). Other researchers have also reported enhanced evaporation through spraying (12). Performance is affected by relative humidity, air temperature, rate of application and wind loss. A study based in California noted that evaporation from stationary sprinklers could range between 0 to 50% over short periods and 3 to 4 times more evaporation could occur during the daytime compared to night time in California’s Imperial Valley (13). For a sprinkler system a concern is the water droplet travel when sprayed. The droplets traveled further with increasing diameter (11). The maximum diameter noted in the paper was 0.2 inches (5mm), which traveled 65ft (20m) when released from a nozzle of height 14.5ft (4.5m) at a flow rate of 0.008gpm (5.5×10-4dm3/s) and at a jet inclination of 25o (11). However, in most cases the distance traveled for droplets ranging from zero degrees to ten degrees of nozzle angle was within 15ft depending on the nozzle height (4ft -13ft) for droplet diameters ranging between 0.02 inches (0.5mm) to 0.1 inches (2.5mm) (11). The data provided above were based on fresh or tap water and not on brine. 2.4.2 Cooling tower The cooling tower method has not been researched in detail in the literature with regard to evaporation loss. However, the installation of a cooling tower would ensure that spray droplets are contained, and high wind velocities will not become a source of concern. A cooling tower is a heat rejection device that releases heat into the atmosphere by cooling a water stream to a lower temperature. The heat raises the air temperature and relative humidity. During the cooling process a small amount of water evaporates causing the overall temperature to further reduce. Cooling towers can be cross-flow, counter flow or parallel flow depending on the airflow direction. Water is pumped to the top and flows to the bottom and is usually sprayed or dripped through internal fill material to increase the efficiency of the mixing of air and water (14). There are three ways water is lost in a cooling tower: drift, blowdown and evaporation, which is the most significant of the three (15). Blowdown is water that is removed from the recirculating cooling water to reduce contaminant buildup in the tower water (14). Drift is a loss of water from the cooling tower in the form of mist carried out of the tower by an air draft (14). Drift is usually in a range of 0.002-0.2% of the water circulation rate (15). According to ASHRAE evaporation loss averages approximately 1% for each 12.6oF (7oC) drop in water temperature (15). Another estimate is a “loss of 1.2% of the rate of flow of the recirculating water passing through the tower for every 10oF decrease in water temperature”(14). The performance of a cooling tower is governed by three important characteristics: the temperature difference between the inlet and outlet water flow, the dry bulb and wet bulb temperature difference, i.e., the humidity and finally the maximum possible temperature difference observed in a cooling tower.


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While most studies have focused on reducing evaporative losses in cooling towers, for this scenario the focus is on maximizing the evaporation loss in the towers and hence from the ponds. A study on the performance of a cross flow cooling tower installed in the south of Tunisia showed that on an annual basis the actual water lost by evaporation represent 4% of the total flow rate (16). 3 EVALUATION OF ALTERNATIVE APPROACHES Each of the methods discussed above have their advantages and limitations. In this section, the potential of each of the four methods is evaluated. However, in general there is a lack of information required for a comprehensive design and cost analysis. 3.1 WAIV method The WAIV study (1) used brine with TDS concentration of 16-18 g/L and was supersaturated with respect to calcium. However, the authors did not do a parametric study involving the influence of the concentration of the brine on the efficiency of the system. To design this method an optimum area of fabric would have to be determined. It would also involve the development of a design for overhead tanks (size and number) for each pond. The study also fails to give a detailed insight into the influence of different weather conditions on the method i.e. the influence of humidity and wind speed on the evaporation rate. To determine the practicality of the method controlled experiments will have to be done. In a search for more information, the company who created this method was contacted and a patent search was completed which turned up no new information. There was no response from emails to the company either. 3.2 Wetted floating fins The application of this method depends on the optimization of the number of fins and the dimensions of the fins. Based on the study previously described (9) a spacing of five times the fin height was recommended. This spacing was estimated to result in a 24% enhancement of evaporation. Materials for the fins’ cover will have to be chosen to obtain the best hydrophilic/hydrophobic relationship to maximize evaporation. There is likely to be a tradeoff between the wicking ability of the fabric and the rate of evaporation from the fabric. Calculations based on literature data show that the capitalized cost of evaporative capacity per gallon per year through the adding of 700 solid fins is 64 cents using a cotton fabric (Appendix A) for additional evaporation of 24%. The cost reduced to 2 cents per gallon of additional evaporative capacity per year if an aluminum screen is used instead of a flat pane. The calculations were based on a fin height of 3 inches of which 2 inches was above water, keeping in accord with the literature. A higher fin height would allow more of the boundary layer to be accessed by the fin. A small experiment conducted in our laboratory indicates that conventional fabrics have enough wicking ability to allow a greater fin height to be wetted. One inch of cotton fabric was dipped in a 3.5 inches deep pan ( 27 16′′ ′′× ). A height of 12 inches was reached after 24 hours. The experiment was repeated for 3 hours with a Dri-Fit fabric (82% polyester, 18% spandex) and a height of eight inches was seen. Cost and the ability of water to evaporate from the fabric would further influence the choice of fabric. The experiments (9) have used fresh water without added salts or dissolved solids. Incorporating the influence of the solids on the wicking as well as the required


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maintenance would definitely result in higher costs than those estimated but could still be acceptable. This remains to be investigated. 3.3 Salt tolerant plants An increase in evaporation of 30% was reported (7) for an 840 gallon/day application with 100,000 mg/L of total dissolved solids and about 60,000 mg/L of chloride. Higher removals may be possible, if low TDS effluent streams can be identified and selectively treated with this method. Overall, this approach looks attractive with the potential of generating revenue if a suitable market is available for the plants grown. The attractiveness of the halophyte as a potential feed will have to be judged to ensure future revenue. The suitability of the weather conditions to the respective halophyte will also have to be considered in detail to ensure their growth. 3.4 Spray method The spray method it is an energy-consuming, active system. This requires at the very onset pumping of the saline water into either nozzles or cooling towers. Considering 2% evaporation from a single nozzle the cost of additional evaporation capacity per gallon per year for electricity for pumping (60psi and 60% efficiency) is 7 cents (Appendix B). Lower pump pressures are probably feasible. The optimization of the sprinkler system would be dependent on the nozzle height, number of nozzles and diameter of spray. The cooling tower method would require a greater capital input for items such as the tower structure and pumps of higher capacity but should offer greater containment of droplets. A cooling tower with water circulation rate of 14gpm, 15oF cooling (from 105oF to 90oF) and wet bulb temperature of 74oF costs $820 (Therflow cooling tower model#TFR-3). For water circulation rate of 90gpm, the cost rises to $2990 (Therflow cooling tower model#TFR-20). Experiments in the literature have been conducted on water without TDS. Hence, in the presence of salt and other minerals the sprinkler size and maintenance would be of significant concern so as to avoid any blockage. For a large facility, the chances of the spray drifting out of the pond is minimal, except during high wind conditions. Hence a higher pumping rate and a larger diameter of spray could be considered for both systems. For the cooling towers the amount of water circulated and the extent of cooling occurring would have to be optimized to achieve the best balance between maximizing evaporation and minimizing cost. A higher circulation rate would incur higher pumping costs and higher cooling tower installation costs but would also increase evaporation. The cost of maintenance and installation of cooling towers would also play a significant role. 4 CONCLUSIONS

A literature review identified four options for enhancing the performance of evaporation ponds for which some performance data are available: wetted floating fins, salt tolerant plants, the WAIV process, and spray methods. Only small-scale experimental results are available for the WAIV and wetted fins processes. Full-scale data are available for the spray method and salt tolerant plant methods. This literature review cannot identify a preferred alternative for a particular application with any degree of confidence, but some conclusions based on available information are summarized below.


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The WAIV process has the greatest potential to increase evaporation, as increases of 13-fold are reported over open water on an equivalent footprint basis. However, this method requires a large amount of fabric and a pumping system, and would continually consume electricity. A cost-effectiveness evaluation has not been reported in the literature for this system. The remaining three methods are reported to increase evaporation by 24% (wetted fins) to 30% (salt-tolerant plants) to 35% (spray evaporation). Increases could be significantly larger for the salt-tolerant plant method if lower TDS waste streams could be selectively treated. These differences in reported performance are small compared to the degree of uncertainty in actual, full-scale performance at a given site. Thus, selection among these processes may be driven by other factors, such as complexity of implementation and cost-effectiveness. The use of salt-tolerant plants is probably the most complicated of these three (i.e., excluding the WAIV process) as it requires at least some expertise in agriculture. The economics of the process were not evaluated here, but it is reported to be cost-effective (7). The use of wetted floating fins appears to be the simplest process with spray evaporation falling between this method and the salt-tolerant plant method in complexity. The cost-effectiveness of the wetted fins approach and of electricity required for the spray method appeared favorable based on preliminary cost models.

Cost will rise somewhat as additional factors are included in the models, but an effort was made to identify major costs. Based on the available data and literature, it would seem that the wetted fins approach is attractive as a retrofit option, as it appears to be the most cost effective in the preliminary analysis conducted here and is probably the least complex to implement. It does have the lowest reported increase in evaporation capacity. If these methods are implemented for a new facility, they would avoid capital costs by reducing the required footprint of the facility. Thus, costs should be based on the combined cost of the pond construction plus the evaporation enhancement method:

tenhancemenalconventionenhancealconventionalconvention CostQFCostQtFacility ***cos += where Qconventional is the annual evaporative capacity of the pond without any enhancement, Fenhance is the fraction by which the enhancement increases capacity, and Costenhance and Costconventional are the capitalized unit costs of the enhancement and the conventional pond, respectively. The overall units cost is the facility cost divided by the total capacity:

alconventionenhancealconvention

tenhancemenalconventionenhancealconventionalconvention

QFQCostQFCostQ

tUnit*

***cos

++

=

which simplifies to:

enhance

tenhancemenenhancealconvention

FCostFCost

tUnit+

+=

1*

cos

In the following examples, it is assumed that pond construction costs $1/gallon annual capacity. Using the preliminary cost estimates as an example, implementing the spray evaporation method costs an additional $0.05/gallon annual capacity and enhances capacity by 24%:

82.024.01

24.05.01cos =+

∗+=tUnit


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The spray method is estimated to increase evaporation by 35% and cost $0.07/gallon annual capacity: This analysis would suggest that the spray method is favored for new ponds. Although it is more expensive than the wetted fins approach on a per unit treatment capacity basis, it provides a greater enhancement to the pond’s capacity, which avoids the cost of additional pond area, leading to an overall lower facility cost. This analysis is provided as an example analysis only. At this point costs information is too preliminary to determine which approach would be most cost effective in practice.

This research has identified several options for enhancing the performance of evaporation ponds. Preliminary estimates suggest that these methods may be cost-effective. Further research, ideally using a combination of physical experiments and mathematical modeling methods would be required to assess the performance of alternative designs and identify an appropriate conceptual basis of design.

ACKNOWLEDGMENTS Financial support from Musco Olives, Inc. is gratefully acknowledged. REFERENCES (1) Gilron, J.; Folkman, Y.; Savliev, R.; Waisman, M.; Kedem, O., WAIV-wind aided

intensified evaporation for reduction of desalination brine volume. Desalination 2003, 158, 205-214.

(2) Ahmed, M.; Shayya, W., H.; Hoey, D.; Al-Handaly, J., Brine disposal from Inland desalination plants. Water International June 2002, 27, 194-201.

(3) Kingdon, K. H., Enhancement of the evaporation of water by foreign molecules adsorbed on the surface. Journal of Physical Chemistry 1963, 67, 2732-2737.

(4) Barthakur, N. N.; Arnold, N. P., Evaporation rate enhancement of water with air ions from a corona discharge. International Journal of Biometerology 1995, 39, 29-33.

(5) Gault, T., Evaporation enhancement through the use of sprays. Plant/Operations Progress 1986, 5, 23-26.

(6) Winans, D. C. 1967. The relative stability of six dyes in a saline brine of constant salinity [Master of Science Thesis]. New Mexico:New Mexico State University.

(7) Keyes, C. G. 1966. The effect of dye on solar evaporation of brine [Doctor of Science Thesis]. New Mexico:New Mexico State University.

(8) Bloch, M. R.; Farkas, L.; Spiegler, K. S., Solar evaporation of salt brines. Industrial and Engineering Chemistry 1951, 43, 1544-1553.

(9) Guitierrez, O., R. Roman, Effect of wetted floating fins on water atmosphere heat exchange. Journal of Energy Engineering April 1993, 119, 32-42.

(10) Negri, M. C.; Hinchman, R. R.; Settle, T. Salt tolerant plants to concentrate saline waste streams. In Phytoremediation; Schnoor, J., L., Zehnder, A., Eds.; John Wiley and sons, 2003.

(11) Lorenzini, G., Water droplet dynamics and evaporation in an irrigation spray. American Society of Agricultural and Biological Engineers 2006, 49, 545-549.

76.035.01

35.07.01cos =+

∗+=tUnit


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(12) Burt, C. M.; Mutziger, A. J.; Allen, R. G.; Howell, T. A., Evaporation Research: Review and Interpretation. Journal of irrigation and drainage engineering 2005, 131, 37-58.

(13) Hermsmier, L. F., Evaporation during sprinkler application in a desert climate. Americal Society of Agricultural Engineers 1973, 73-216.

(14) Water management options: Cooling and heating. North Carolina Department of Environment and Natural Resources Division of Pollution Prevention and Environmental Assistance, 2006. Available: http://www.p2pays.org/ref/04/03101.pdf [accessed July 20 2007].

(15) Qureshi, B., Ahmed; Zubair, A. S., Prediction of evaporation losses in wet cooling towers. Heat transfer engineering 2006, 27, 86-92.

(16) Kairouani, L.; Hassairi, M.; Tarek, Z., Performance of cooling tower in south of Tunisia. Buiding and Environment 2004, 39, 351-355.


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Table 1: Evaporation Enhancement Options*

Alternative Physical Basis Potential Improvement Comments Reference(s) WAIV Water drips from

elevated tank and evaporates from vertical hanging cloth.

13-fold increase in evaporation

Only tested with TDS up to 18,000 ppm (“considered severest test”) and in small-scale applications.

(1)

Wetted floating fins (aluminum fins)

"Boundary layer breaker" and adds additional area for exchange.

24% increase in evaporation using cotton fabric for covering. Improvement may be greater in windier environments.

Fins must be perpendicular to wind. No information on large-scale applications is available. The effects of waves and differing salinity levels have not been studied and may affect performance.

(9)

Salt tolerant plants

Plants absorb water and filter.

30% at ~90,000 mg/l TDS, greater at lower TDS.

Tested in an 840gallon/day application. In the study, the plants grown were suitable for cattle to graze on (without removing salt crystals).

(10)

Fountain or misting during daytime

Spraying water droplets into the air resulting in increased air water interface.

Overall increase of evaporation is 30-35%. Results show that 2-15% of water sprayed is lost due to evaporation from a single nozzle.

Overall evaporation based on 24 nozzles in an evaporation pond of area 19264ft2. Most data based on fresh/tap water.

(5,11,12)

Cooling tower

Water is sprayed from the top into air resulting in lowering of the water temperature. Some water evaporates during the process.

Evaporation loss averages approximately 1% for each 12.6oF (7oC) drop in water

According to ASHRAE evaporation loss averages approximately 1% for each 12.6oF, drop in water temperature. The focus has been on minimizing evaporation losses in cooling towers. However, the information available can be used to optimize a cooling tower for this application.

(15)

*Maximum evaporation from open water surface is 0.16 inches/day based on observational data from NOAA using a class A evaporation pan (47.5 inch diameter and 10 inches deep) for the month of July 2006.


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Appendix A Determining capitalized cost for the wetted fin approach

Pan evaporation rate 0.13 inches/day Evaporation rate increase by fins (24%) 0.24

Additional evaporation 0.031 inches/day Pond surface area 204732 sq.ft Total evaporation 2218 cubic.ft/day 809544 cubic.ft/year 16590 gallons/day 6055392 gallons/year With fin Added evaporation 532 inches/day 1453294 gallons/year Fin dimensions L 270.00 Ft

H 3.00 Inches Fin height based on

literature. 0.25 Ft Height above water surface 2.00 Inches 0.17 Ft Width 0.50 Inches 0.04 Ft

Spacing between each fin 10.00 Inches Spacing is five

times the fin height 0.83 Ft Length of the pond 700.00 Ft No. of fins 700.00 Exposed area of each fin 45.00 sq. ft Total area of fins 47250.00 sq. ft 77.3*

Cost of Aluminum sheet (0.5" by 3" by 270")

$ 1,324.80 Quote

screen option per 3 hundred feet cost for 600 feet of screen

Cost of Cotton/yd $ 1.00

Bower Fabrics, by phone

Total cost of Aluminum required $ 927,360 Solid plate 24349.5

Screen

Total cost of Cotton $ 5,250

Total cost of materials $ 932,610 $ 29,599.50 cost of screen and fabric

Cost/gallon/year $ 0.64 $ 0.02 * http://www.technologylk.com/product_view.aspx?&source_ID=nextag&product_ID=9615


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Appendix B

Calculations regarding capitalized cost of pumping for spray evaporation

0.13 evaporation in inches/day 0.35 percent increase due to sprayer

0.0455 additional evaporation in inches per day size of pond

350000 ft2 area 3792 total evaporation ft2/day

28362 gallons/day

10,352,008 total evaporation capacity in gallons/year

1327 additional evaporation due to sprayer system, ft2/day

9926 additional evaporation in gallons/day

0.02 fraction of pumped water that is evaporated 496,329 gallons pumped/day

1.52 acre feet pumped/day

23.58 cost/acre foot for 60 PSI at .1 $/kwhr and 60% efficiency

http://www.olivenhain.com/PDF/pressure.pdf

http://westlandswater.org/wtrcon/handbook/pump.htm

35.9 $/day 13109 $/year

262190 capitalized cost

3,623,203 gallons/year 0.072 capital cost/gallon/year capacity


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