Recycling and Reuse 74 IDA J OURNAL | F IRST Q UARTER 2010 WWW. IDADESAL . ORG vaporation ponds are lined detention basins into which wastewater is discharged and held to allow evaporation to decrease the water’s volume. Be- cause the cost of wastewater disposal depends on volume, not concentration, it is more cost-effective to dispose of 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 energy-intensive methods and are used primarily in semi-arid regions where land costs are low. Evaporation ponds have some disadvantages, including the expense of impervious liners to prevent seepage of sa- line water into aquifers and the need for large quantities of land when high levels of evaporation are required (Gil- ron et al, 2003). Research has focused on finding ways to increase evaporation rates, which would result in reduc- ing pond size, liner costs, and land (Ahmed et al, 2002). This report evaluates available alternatives to enhance evaporation from these ponds. Literature Review Several researchers have explored ways to enhance evap- oration rates. For example, water’s hydrogen bonds may be weakened by attaching foreign molecules to the sur- face, resulting in increased evaporation rates (Kingdon, 1963). The gases examined included helium, nitrogen, butane, and oxygen, with butane working best. Another method used electric wind created at 5,250 V to produce turbulence in the water, resulting in a four-fold increase of evaporation rates (Barthakur and Arnold, 1995). Other researchers have explored the possibility of adding dye to maximize use of solar energy (Winans, 1967; Keyes, 1966; Bloch et al, 1951). A colored solution would absorb more solar energy, increase temperature, lower surface tension, increase saturation vapor pressure, and subse- quently increase evaporation rate (Ahmed et al, 2002). Researchers observed increased evaporation with the ad- dition of methylene blue dye (Keyes, 1966) and recom- mended adding 3.5 grains of dye per ft 3 of brine (Bloch et al, 1951). Other possible methods to enhance evaporation in- clude spraying the brine, increasing pond turbulence, passing the brine over inclined rough surfaces, and creat- ing airflow over the pond (Ahmed et al, 2002). Among the various alternatives, the following options were targeted for detailed review (Table 1): n Wind-aided intensified evaporation (WAIV) n Wetted floating fins n Salt-tolerant plants n Droplet spraying E Desalination of brackish groundwater is an increasingly important option for inland communities. However, disposing of concentrated saline residual waste streams in evaporation ponds is land intensive. Large facilities might be concerned that this technology is one of the few treatment methods that offers decreasing returns to scale because of increasing boundary-layer resistance for larger ponds. This study evaluated several innovative options for improving evaporation pond performance, including fabric evaporators, wetted-boundary layer breakers, salt-tolerant plants, and droplet spraying. Cost models were developed for boundary-layer breakers and droplet spraying. Incremental costs and evaporation enhancements are compared with site-specific cost information for a wastewater treatment facility in California’s Central Valley. Results indicate that boundary-layer breakers and spray technologies are cost-effective compared to a simple pond expansion. Boundary-layer breakers appear to be more cost-effective per gal of incremental capacity but have a lower evaporation enhancement capacity compared to droplet spraying (24 percent vs. 35 percent). 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 as a retrofit to an existing facility are preferred if they provide sufficient additional capacity to avoid the need for pond expansion. Innovative Technologies Increase Evaporation Pond Efficiency Shamia Hoque, Terry Alexander, and Patrick L. Gurian