(702e) Membrane Distillation Crystallization for Treating Mixed Salt Brines from Inland Desalination

The inland brine stream management has higher costs compared to seawater desalination plants. The increased cost is attributed to the need that current brine disposal methods have in order to meet strict environmental regulations. Brine disposal can be mitigated via a zero liquid discharge (ZLD) system, as it aims to recover and reuse the water component of the brine coming from the desalination facility, while simultaneously recovering salts.

Membrane distillation crystallization (MDC) is an ideal technique to achieve ZLD because it combines the membrane distillation (MD) process with crystallization to recover solid salts and produce high-quality water. MD is a thermally-driven separation process that utilizes a hydrophobic, microporous membrane. The driving force of MD is the temperature-induced vapor pressure difference between the brine and distillate. MD can treat saturated brines without requiring significantly higher energy inputs compared to lower salinity feeds.

In this work an MDC system was developed to treat RO brine from inland desalination. A bench-scale MDC setup was created with a flat-sheet direct contact MD module and a custom-made, acrylic six-tray cascading crystallizer. The salt selectivity of the crystallizer was predicted from the PHREEQC solubility software, which provides the saturation indexes of the salts. The feed solution used in these experiments was a mixed salt solution with a known inland brine composition. The results compared MDC performance to MD alone under the same MD conditions, and showed that MDC can effectively treat mixed salt solutions and achieve ZLD.