Shellfish to the Rescue

The United Nations estimates that globally, nearly 95 trillion gallons of wastewater are produced every year - roughly equivalent to 41 years of drinking water for the entire human population.  Last month, the Global Commission on the Economics of Water (GCEW) reported that only 20% of wastewater is currently treated, with far less than that being recycled.  These factors are contributing to a global shortage of clean water.  The GCEW report anticipates that demand for freshwater will outstrip supply by nearly 40% in just seven years.   

One way that nature helps clean the waters is through oysters.  They eat by filtering water, removing nitrogen, phosphorus, and other pollutants from the water.  In fact, one full-grown oyster can filter up to 50 gallons of freshwater per day.  Another shellfish, mussels, has been nicknamed the "vacuum of the sea."  As they pump and filter the water through their gills to feed and breathe, mussels take in phytoplankton for nourishment, along with microplastics, pesticides, and other pollutants.  Marine biologist Leila Meistertzheim estimates that one mussel can filter up to 25 liters of water every day. 

Every year, the textile industry uses 1.3 trillion gallons of water to dye garments, and this accounts for 20% of industrial wastewater globally.  Most of this water, now loaded with harmful chemicals and dyes, then flows untreated into rivers and streams.  While the highest concentrations of textile-derived water pollution can be found in China and Bangladesh, it should be a global concern since Earth's water cycles are inextricably linked.  Led by Dr. Hassan Arafat, professor of chemical engineering and Director of the Research and Innovation Center in Graphene and 2D Materials, researchers at Khalifa University in Abu Dhabi, United Arab Emirates (UAE), studied ways to help clean up these dyes and other pollutants from industrial wastewater.  

The team took inspiration from the protein in mussels' "beards," the strong, sticky threads that help the shellfish attach to rocks and reefs.  They created a new nanomaterial using a polymer called polydopamine, and modified it with an ionic liquid as a solvent to create the adsorbent material.  Researchers then tested their nanomaterial on a red-orange dye called Alizarin Red S, and published their findings earlier this year in Chemical Engineering Journal.  The researchers targeted this specific anionic dye because there are not many effective methods to remove these types of dyes from water.  "We're looking at the efficiency and also the environment at the same time," said Dr. Enas Nashef, who is part of the research team.  The scientists used methanol to put their nanomaterial through four cycles of adsorption-desorption without any significant performance decrease or loss of structural integrity.  

Dr. Nashef is also working to find solutions for cleaning more than just textile dyes from water.  He is developing a different nanomaterial that he says could remove viruses from hospital wastewater - an innovation that could help manage the spread of future pandemics.  These water-cleaning polymers could also help to make the desalination processes more sustainable, which is an important factor in the Middle East, where freshwater sources are scarce.  Desalination plants require a lot of energy to remove salt from water, so using membrane-based nanomaterials in pre-treatment would cut the energy needed to clean the water. 

Water shortage can be divided into two main groups: resource-induced and pollution-induced.  The work these scientists are doing will hopefully help with both causes of water shortage.  It will be interesting to see how effective this technology is when put to use on a wider scale and how else it can be applied to make the planet a cleaner place.