10 Innovations in Water Purification

Direct-Contact Membrane Desalination
A desalination plant in Oman. The process of desalinaton is expensive but the new process of DCMD promises to make it cheaper and more efficient. Franz Aberham/Photographer's Choice/Getty Images

If we could tap the vast oceans as a source of drinking water, everyone would have more than enough. But that means removing the salt, which is inefficient and costly using existing technology. That's why a new process, developed by New Jersey Institute of Technology chemical engineering professor Kamalesh Sirkar, has such dazzling promise. In Sirkar's direct-contact membrane distillation (DCMD) system, heated seawater flows across a plastic membrane containing a series of hollow tubes filled with cold distilled water. The DCMD's tubes have tiny pores, which are designed so that they can be penetrated by the water vapor which collects on them, but not by salt. The vapor diffuses through the pores and is drawn off, to be condensed again into liquid water.

According to Sirkar, his system is extremely efficient -- it can produce 80 liters (21 gallons) of drinking water per 100 liters (26 gallons) of seawater, about twice what existing desalination technology can produce. One potential downside of DCMD is that it requires a steady, inexpensive source of heat in order to prevent the water temperature on either side of the membrane from equalizing. But there's the possibility that DCMD systems could someday recycle waste heat from shore-based factories and offshore oil drilling operations, making it a win-win for everybody [source: Greenmeier].