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May 2, 2022

MIT researchers create a portable desalination unit that can run off a single solar panel

Filed under: Emerging Tech,My Thoughts,Science Related — Suramya @ 2:33 AM

The lack of drinking water is a major problem across large portions of the world and over 2 billion people live in water-stressed countries. According to WHO at least 2 billion people use a drinking water source contaminated with feces. On the other side, places near the sea have to deal with salt water contamination of their drinking supply. If we can desalinize sea water cheaply and easily then it will be a great boon to world.

There are existing technologies that convert sea-water to drinking water but they require massive energy supply and large scale plants which are very expensive to make. To resolve this issue MIT researchers have been working on creating a portable desalination unit that generates clear, clean drinking water without the need for filters or high-pressure pumps. Since the unit doesn’t use filters or high-pressure pumps the energy requirement is low enough that it can be run off a small, portable solar panel.

The research team of Jongyoon Han, Junghyo Yoon, a research scientist in RLE; Hyukjin J. Kwon, a former postdoc; SungKu Kang, a postdoc at Northeastern University; and Eric Brack of the U.S. Army Combat Capabilities Development Command (DEVCOM) created this and the initial prototype has worked as expected. Their research has been published online in Environmental Science and Technology.

Instead, their unit relies on a technique called ion concentration polarization (ICP), which was pioneered by Han’s group more than 10 years ago. Rather than filtering water, the ICP process applies an electrical field to membranes placed above and below a channel of water. The membranes repel positively or negatively charged particles — including salt molecules, bacteria, and viruses — as they flow past. The charged particles are funneled into a second stream of water that is eventually discharged.

The process removes both dissolved and suspended solids, allowing clean water to pass through the channel. Since it only requires a low-pressure pump, ICP uses less energy than other techniques.

But ICP does not always remove all the salts floating in the middle of the channel. So the researchers incorporated a second process, known as electrodialysis, to remove remaining salt ions.

Yoon and Kang used machine learning to find the ideal combination of ICP and electrodialysis modules. The optimal setup includes a two-stage ICP process, with water flowing through six modules in the first stage then through three in the second stage, followed by a single electrodialysis process. This minimized energy usage while ensuring the process remains self-cleaning.

Video demonstration of the process

The prototype device was tested at Boston’s Carson Beach and was found to generate drinking water at a rate of 0.3 liters per hour, requiring only 20 watts of power per liter during the use. As you can guess this is pretty amazing. If the device can be mass-produced it will help reduce the scarcity of drinking water in the world without requiring massive amounts of energy which would cause other climate impact.

One downside of this kind of machine is that it creates a byproduct of highly saline water as the salt from the pure water is mixed with the waste water. Releasing this water in the ocean has a huge impact on the sea life as the water suddenly becomes too saline for them. If the water is allowed to seep into the land then it will reduce the fertility of the soil due to the increased salt in the soil. In addition to making the device commercial we also need to do research on what we should do with the waste water generated so that the adverse impact of the product can be offset.

Source: MIT News: From seawater to drinking water, with the push of a button

– Suramya

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