Tidying Up the Rivers at No Further Environmental Cost

Human beings can credit their progression to a variety of factors, and yet none deserves the honor more than our simple tendency to grow under all circumstances. This tendency, in particular, has brought the world some huge milestones, with technology emerging as quite a major member of the stated group. The reason why we hold technology in such a high regard is, by and large, predicated upon its skill-set, which guided us towards a reality that nobody could have ever imagined otherwise. Nevertheless, if we look beyond the surface for one hot second, it will become abundantly clear how the whole runner was also very much inspired from the way we applied those skills across a real world environment. The latter component, in fact, did a lot to give the creation a spectrum-wide presence, and as a result, initiated a full-blown tech revolution. Of course, the next thing this revolution did was to scale up the human experience through some outright unique avenues, but even after achieving a feat so notable, technology will somehow continue to bring forth the right goods. The same has turned more and more evident in recent times, and assuming one new discovery ends up with the desired impact, it will only put that trend on a higher pedestal moving forward.

The researching team at Massachusetts Institute of Technology has successfully developed a zwittertronic hydrogen system, which is designed to eliminate micropollutants from water in a more efficient and sustainable manner. Before we get into the solution, though, we must try and unpack the making of micropollutants first. You see, these are chemically diverse materials that can be harmful to human health and the environment, even though they are typically found at low concentrations (micrograms to milligrams per liter) relative to conventional contaminants. Interestingly enough, micropollutants can either be organic or inorganic, forming specific categories where organic micropollutants are mostly carbon-based molecules and include pesticides and per- and polyfluoroalkyl substances (PFAS), known as forever chemicals. On the other hand, inorganic micropollutants pack together metals like lead and arsenic. As both the types are highly detrimental and pervasive, the world has already seen many efforts geared towards curbing their presence, efforts that eventually saw activated carbon becoming the ultimate benchmark around here. However, it has been repeatedly established that making filters with activated carbon is energy-intensive, and therefore, requires very high temperatures in large and centralized facilities. To give you a gist, an estimated four kilograms of coal is needed to make one kilogram of activated carbon. Such requirements ensure that you end up losing a hefty amount of carbon dioxide to the environment, and that’s exactly why according to the World Economic Forum, global water and wastewater treatment accounts for 5% of annual emissions. Leave that, Environment Protection Agency’s data reveals that, in the US alone, drinking water and wastewater systems account for over 45 million tons of greenhouse gas emissions annually. Enter zwittertronic. Picked up from the German word “zwitter,” meaning hybrid, zwitterionic molecules are those boasting an equal number of positive and negative charges. Traditionally, such molecules have been used as coatings on membranes for water treatment due to their non-fouling properties, but the new study takes up a slightly approach. It applies them to form the scaffold material, or backbone within the hydrogel – a porous three-dimensional network of polymer chains that contains a significant amount of water.

“Zwitterionic molecules have very strong attraction to water compared to other materials which are used to make hydrogels or polymers,” said Devashish Gokhale, a Ph.D. student in the lab of Professor Patrick Doyle, who led the research.

The work on this new development actually started back in 2019, when Doyle and his group realized that their approach of using hydrogels to formulate drug molecules into pill format can also be applied for treating polluted water at scale. In present, the bet was on micelles present within hydrogels. In case you weren’t aware, micelles are spherical structures that form when molecules called surfactants come in contact with water or other liquids. The method succeeded in synthesizing micelle-laden hydrogel particles that would, in turn, soak up micropollutants from water like a sponge. Furthermore, unlike in activated carbon mechanism, the hydrogel particle system posed no collateral concerns as it was all made from environment-friendly materials. Enhancing the system’s prospects even more is the fact that its underlying material was made entirely at room temperature, a feature which ensures the method has a much greater promise when it comes to sustainability than activated carbon.

Another detail worth a mention here would be how the new method makes a pledge to achieve rapid elimination of micropollutants. It achieves the said objective, thanks to zwitterionic molecules’ unique properties that confer high porosity. In a more concrete sense, the initial tests show that hydrogels can eliminate six chemically diverse micropollutants at least 10 times faster than commercial activated carbon. This particular face becomes especially crucial in places where the amount of time water can spend inside the operational filtration unit is limited, otherwise known as contact time. For instance, in municipal-scale or industrial-scale water treatment systems, contact times are usually less than 20 minutes and can be as short as five minutes.

“Most technologies focus only on specific molecules or specific classes of molecules. So, you have whole technologies which are focusing only on PFAS, and then you have other technologies for lead and metals. When you start thinking about removing all of these contaminants from water, you end up with designs which have a very large number of unit operations. And that’s an issue because you have plants which are in the middle of large cities, and they don’t necessarily have space to expand to increase their contact times to efficiently remove multiple micropollutants,” said Gokhale.

Moving on to the development’s flexible nature, it refers to system’s compatibility with a diverse set of materials. Such a feature means micropollutants can bind to many different sites within the hydrogel platform. To give you some context, even though organic micropollutants bind to the micelles or surfactants, and inorganic micropollutants bind to the zwitterionic molecules, they and other chelating agents can be easily swapped in and out to tune the system with different functionalities based on the profile of the water being treated. The stated swapping also doesn’t ask for any change in the design or synthesis of the hydrogel platform. All in all, the given agility makes it possible for the zwitterionic-centric system to rapidly remove multiple contaminants at lower concentrations without the need for large industrial units. Hold on, there is more, considering we still haven’t discussed that the particles of our new technology can also be regenerated and used more than once or just a few times. One can realize the same by putting these particles in an ethanol bath to wash way the micropollutants, and thus, make the system as good as new.

Currently being piloted through a number of commercialization programs at MIT and in the greater Boston area, the new system’s uses cases already stretch across a wide spectrum, ranging from large-scale industrial packed beds to small-scale, portable off-grid applications.

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