By Ansel Oommen via Living Green Magazine
A little over a centimeter long, the common duckweed, Spirodela polyrrhiza, is often found colonizing ponds and lakes in a carpet of green. With a global distribution, the duckweed family claims the Guinness for some of the smallest, simplest, and fastest growing plants of the botanical world. Yet, despite their unassuming nature, these tiny fronds are making a huge splash in wastewater management.
Duckweeds are natural super-filters, sucking up minerals and organic nutrients from the water, which then accumulate into the plants’ biomass.
For decades, major cities have been trying to tackle the growing waste problem with varying levels of success. Population growth and modern farming practices have led to unparalleled amounts of sewage. Add industrial byproducts and the resulting soup is chock full of disease causing pathogens, pesticides, and organic pollutants. Needless to say, it is an environmental health crisis.
Left untreated, these chemicals poison freshwater supply and rob it of oxygen. Large amounts of nitrogen and phosphorus (typical of human and animal waste), for example, can trigger algal blooms that choke out aquatic wildlife, turning the water a sickly brown, red, or green. Indeed, the Environmental Protection Agency cites wastewater pollution for “frequent occurrences of low dissolved oxygen, fish kills, algal blooms, and bacterial contamination.”
Such cases are sadly the norm. The Great Lakes contain one-fifth of the world’s surface freshwater and yet billions of gallons of untreated sewage are dumped into its waters each year. In addition to disrupting the ecosystem, the contamination prevents patrons from enjoying its beaches.
But the common duckweed provides an almost magical solution. Duckweeds are natural super-filters, sucking up minerals and organic nutrients from the water, which then accumulate into the plants’ biomass. This process, called bioremediation, is not only safe, but effective. Central to the duckweeds’ success is their ability to grow at a rapid rate and hence, their ability to consume large quantities of contaminants such as ammonia, lead, and arsenates. In fact, duckweeds can double their weight in one to two days under ideal conditions.
Moreover, the roots harbor useful bacteria and algae that further speed up the process. Brazilian research published in Bioresource Technology has demonstrated the plant’s tremendous potential. As the world’s third largest producer of pork, Brazil has used duckweed ponds to treat its swine waste.
When grown on swine wastewater, the duckweed Landoltia punctata was shown to remove 98 percent of the total nitrogen and ammonia content, and 94 percent of the total phosphorus. Considering these are the main agents of eutrophication, or nutrient pollution, the results are groundbreaking. If that wasn’t enough, L. punctata also improved levels of dissolved oxygen, crucial for the health of aquatic ecosystems.
Once the plant has done its job, it is skimmed off the surface and used as a nutritious feed for livestock. A combo of ultraviolet light and ozone destroy any existing pathogens. But despite the benefits, duckweed implementation remains an upstream battle.
For the read of the story, head on over to Living Green Magazine