Processes for water reclamation

Water treatments fall into two broad classes; those that remove or destroy specific classes of pollutants, i.e. color, metal ions, hardness, sediment, bacteria, etc., and those that remove water from nearly all of the pollutants. The first class includes sedimentation, biological treatment by microbes, chemical precipitation, adsorption on active carbon or ion exchange resins, and disinfection. The second class includes distillation, freezing and reverse osmosis (RO). The first class are the least expensive in terms of energy and have a long history of successful use on a large scale to reclaim water containing sewage. Most of the second group are energy intensive and have been used primarily on a moderate scale. All processes, except disinfection, leave a residual sludge or brine that contains a substantial quantity of water. Many of the problems of treating waste water for reuse on Earth stem from the fact that waste water carries pathogenic organisms from one location to another and may spread disease over long distances. In a closed group, such as in a Space Station, there are so many other routes for transfer of microorganisms, i.e. in the air, on surfaces, by hand-to-mouth, that undue emphasis on disinfection of water is inappropriate. Successful examples of water reuse on Earth are reviewed in terms of their possible application in space.