Water recovery is an essential capability for long-term space missions because potable water is a vital resource. Wastewater, especially human urine, contains mineral salts that must be removed if the recycled water is to become potable. This paper addresses secondary water processors using distillation. These processors are elements of a complete water recovery system and are used to recover water from urine and brines. Most of the previous work on distillation processors has been devoted to the processing of urine. The most successful urine processors use rotary vacuum distillation.
Vacuum rotary distillation is the process of distillation at reduced pressure in a rotating apparatus. This provides for operation at reduced temperatures and operation in zero-gravity, both of which are desirable for space flight applications. The processors discussed are vacuum rotary distillation with integral thermoelectric heat pump (VRDthp), vacuum rotary distillation with steam ejector compression (VRDec), air evaporation rotary distillation system (AERD), multistage vacuum rotary distiller (MVRD), and vapor compression distillation (VCD). The operation of the processors is described in detail and experimental test results are summarized.
The rotary vacuum distillation technologies were compared on the basis of specific energy consumption, critical technology, and weight. The MVRD approach has the most promise when specific energy consumption and weight are important factors.