Creating Clean Water Using Much Less Energy

As water scarcity is striking more and more people with every passing day the need for cleaner water is getting stronger and higher. Desalination via Reverse Osmosis (RO) has been a viable solution that has been on list for long. It has met the global clean water requirements well, however, the process is a costly one both in terms of money as well as energy. A team of researchers from MIT created some new concept designs for reverse osmosis desalination that would help in enhancing the energy efficiency of other water cleaning techniques as well.

Creating clean water using less energy

The new design works in batches in place of following a consistent method of desalination. The new approach can play a key role in reducing energy usage in upcoming desalination systems. The team’s co-leader, David Warsinger, says, “In traditional RO systems, the entire system is maintained at a steady, high pressure to be able to reach the desired level of water recovery.” Saline water is specifically pumped through a thin membrane that lets water to pass through it but keeps salts and minerals on the surface. Water then permeates through the membrane and the feed solution gets thicker and more concentrated. Warsinger adds, “The commercially-available semi-batch design, called closed-circuit reverse osmosis, or CCRO, recycles the concentrate into the feed stream, so that the feed solution becomes concentrated over time, and pressure in the system can be increased incrementally as needed.”

The team claims that a complete batch design will have the potential to pull efficiency on higher scales and more higher when a closed feed tank will be used. Another co-lead researcher of this team, Emily Tow, adds, “Mixing causes entropy generation, which is the enemy of efficiency. Our model shows how reduced mixing in batch RO improves energy efficiency over CCRO by up to 20 percent. Compared to conventional RO systems, the batch configuration provides up to 64 percent energy savings.” The main trick is the timing. The configuration they have proposed may ramp up with time to follows the osmotic pressure precisely concentrating the batch of salt water. In order to conserve energy, the first new configuration will use a few parts of RO module in form of a strong tank, the other design, however, uses pressure exchanger for enabling saltwater storage atmospheric pressure, Warsinger explains, “The batch system starts with a fixed amount of solution in a circulation tank and passes it multiple times through the RO membranes to collect clean water. With each pass, the concentration of the remaining solution increases and the pressure of the system increases to match its osmotic pressure. This gradual increase eliminates the excess energy needed to maintain the entirety of a continuous system at a high pressure.”