Water recovery from and volume reduction of gray water using an energy efficient evaporator

Abstract

Tests were made under a contract with VEDA Inc. of Alexandria, Virginia, for the United States Navy, Environmental Protection Branch, Annapolis, Maryland. The objectives of the tests were to demonstrate the use of vapor compression distillation to greatly reduce the storage volume of wastewater on US Navy ships during extended missions, examine the quality of the produced distilled water for reuse, and determine energy requirements for the process. Three 55 gal drums of gray wastewater, shipped from Annapolis, were used in the tests at The Water Reuse Technology (WRT) test facility, Alamo, California. The tests were made in a 3 gal/h vapor compression distillation unit using the energy efficient wiped film rotating disk (WFRD) evaporator. Data were collected to determine recovery, evaporator performance, and distilled water and blowdown qualities. The tests were run at an average temperature of 122°F in the evaporator. The results show that recoveries as high as 98.6% are possible. Measured energy consumption by the compressor and rotor (for this small unit) varied from 75 to 90 Wh/gal. Samples of the wastewater, distilled water, and blowdown were collected for analysis. The results of the analysis of the distilled water samples indicate that total suspended solids, fecal coliform, and biological oxygen demand were below the detection limits of the instruments used in the analysis. The chemical oxygen demand varied from below 10 mg/L (detection limit) to 30 mg/L.