Pilot plant studies of novel membranes and devices for direct contact membrane distillation-based desalination

A small pilot plant for direct contact membrane distillation (DCMD) based desalination was built and operated successfully on a daily basis for 3 months. The operation employed hot brine at 64-93 °C and distillate at 20-54 °C. The hot brine was either city water, city water containing salt at the level of 3.5, 6 or 10%, or sea water trucked in from Long Island Sound, CT. One to ten horizontal crossflow hollow fiber membrane modules each having either 2448 or 2652 hollow fibers and 0.61 or 0.66 m2 surface area were combined in various configurations to study the plant performance. The highest water vapor flux of 55 kg/(m2 h) was achieved with two modules in series; the flux varied between 15 and 33 kg/(m2 h) for configurations employing 6-10 modules. The highest distillate production rate achieved was 0.62 gallons per minute (gpm). The membrane modules never showed any sign of distillate contamination by salt. The plant operated successfully with a very limited flux reduction at salt concentrations up to 19.5% from sea water. A mathematical model was successfully developed to describe the performance of the pilot plant with multiple crossflow modules in different test configurations.