Zero discharge desalination
Abstract
Intensive energy consumption and concentrate management are major issues for desalination at inland areas. This work addresses these issues by examining a systems approach for desalination. The systems approach, called zero discharge desalination, combines multiple desalination processes and brine concentration with salinity gradient solar pond (SGSP) technology. In the zero discharge system, the concentrate from desalination processes is reused by solar ponds thereby negating brine disposal, and the solar ponds provide renewable energy to the desalination and brine concentration processes. A multi-effect multi stage (MEMS) desalination unit, a membrane distillation (MD) unit, and a brine concentration and recovery system (BCRS) were tested with the heat generated from the El Paso Solar Pond. The MEMS unit with three-effects and four stages was effectively operated at a first stage vapor temperature range of 60 ∼ 75°C, and at high concentration ratio. This unit produced high quality distillate with a total dissolved solids level of less than 5 mg/liter. Its distillate production rate ranged from 1.6 to 5.0 liter/min, and was significantly affected by flash range, concentration of reject brine, and first effect circulation rate. No significant scaling and fouling were found during the tests. An air gap MD unit with a membrane area of 2.94 m2 was tested with feedwaters in which salinity ranged from 0 to 19%, and operated with variable warm side temperature, transmembrane temperature drop, and circulation flow rate. The distillate flux ranged from 1 to 6 kg/m2-hr, and was strongly affected by the transmembrane temperature drop, instead of the warm side temperature. This observation suggests that heat transfer is the limiting factor for the flux rather than vapor diffusion. The MD unit can produce high quality distillate, however, membrane wetting has a major impact on the quality of product water. The BCRS uses moderate temperature heat to drive evaporative concentration of saline water, and recovers some fresh water. Slurry salt was produced by the BCRS unit, and recharged into the solar pond along with saturated brine. The operational experience and technical advancements of salinity gradient solar pond technology are also presented in this work.
Subject Area
Environmental engineering|Environmental science
Recommended Citation
Lu, Huanmin, "Zero discharge desalination" (2001). ETD Collection for University of Texas, El Paso. AAI3023414.
https://scholarworks.utep.edu/dissertations/AAI3023414