Innovative Technologies Increase Evaporation Pond Efficiency

Abstract

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.