QUACKING THE CODE – Duckweed's Wastewater Treatment Clues

Could aquatic plants actually teach us how to better deal with wastewater treatment, biofuels, antibiotics and other applications? According to a study in the National Academy of Sciences performed by Chinese and Rutgers University scientists, the answer seems to be “yes”.

A new “ long read” DNA sequencing approach retrieved missing sequences to the duckweed species of spirodela polyrhiza—one of thirty-seven species of the aquatic plant—allowing for a close study of the genome. These small, fast-growing plants are found worldwide and have an immune system that adapts to a polluted environment in a way that is different than land plants. The study allowed scientists to identify those genes that functioned to protect the plant species against a wide range of harmful waterborne fungi and bacteria.

It’s believed that the study could lead to the production of duckweed strains for bioreactors and recycle wastes as well as treat industrial wastewater. According to Joachim Messing, professor and director of microbiological studies at Rutgers University–New Brunswick, this new approach to gene sequencing could be a major step forward for analyzing genomes in plants which could lead to many other societal benefits. 

Most industrial processes produce some type of aqueous based waste stream which must be treated before recycling, reusing or discharging into municipal wastewater systems or surface waters. The type of treatment typically needed depends on the type of industrial process and the resulting contaminants. For example, fine, solid contaminant can be removed either using cartridge filters from Graver’s Liquid Process Filter group or using Graver crossflow technologies. Removal of arsenic, lead, and other heavy metals can be accomplished with MetSorb adsorbent products. It’s fascinating to think that these treatments could somehow be aided in the future by these rather common aquatic plants.

So what exactly is duckweed, and why the funny name? Although not really considered a weed due to its growing desirability and usefulness, duckweed floats on or just below the surface of the water. That alone might suffice as a reason, however, the plant is a common food source for ducks and coot and can make up to 10 to 50 percent of their diet. Another reason is that duckweed often migrates by duck. Since they are so tiny they can become attached to duck feet or feathers and their seeds are hardy enough to survive long distances. It’s interesting to imagine how duckweed itself might be used to control contaminants. It grows abundantly in environments with excess nitrogen or phosphate. It’s more likely that filtration experts will seek to learn how it operates in such environments and perhaps develop new ways of thinking about and addressing wastewater treatment. 

While the duckweed breakthroughs are exciting, plant-based water filtration has lately been an area of study as a method for cleaning water. In 2013 an Oxford University student won an international award for his plant filtration system that removes arsenic from water. Moss has also long been studied. Because it has no root system, it absorbs water and nutrients throughout the entire plant. In 2017, researchers in Japan showed how a certain type of moss can absorb a large amount of lead due to a special kind of acid in its cell walls. Later that year, a research group in Sweden showed that a specific type of aquatic moss could help remove arsenic from water. Their study found the moss reduced arsenic levels by 80% in less than an hour as it became bound to the plant’s tissue. Interesting stuff.

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