Duckweed is the smallest flowering plant known to Earth, while also having the capability to double in mass in as little as 16 hours. On top of this, duckweed is abundant in supply, growing in freshwater on every continent except Antarctica. These benefits make duckweed a promising species for numerous applications, from wastewater treatment to biofuels.
Duckweeds look like tiny green speckles with no obvious root, stem, or leaves but instead a frond structure that contains air pockets and ultimately is what allows the duckweed to float on or just below the water surface. Each duckweed has 1 to 3 fronds that are 1/16 to 1/8 of an inch in length.
Duckweeds are monocotyledons (defined as grass or grass-like flowering plants) of the Lemnaceae family and belong to macrophytes (defined as aquatic plants growing in or near water). They can spread quite easily, usually through water channels, and once they find stagnant water they can proliferate so rapidly that they can cover an acre of surface in only a month and a half.
There are different strands, or genera, of duckweed, including Spirodela (giant duckweed), Landoltia (dotted duckweed), Lemna (common duckweed), Wolffiella (bog mat), and Wolffia (watermeal). Where Spirodela is the largest duckweed type, Wolffia is the smallest. Strands can be identified by their size, patterns, and rootlets.
Duckweeds predators include ducks, snails, herbivorous fish like carp, and some birds. They can provide shade to keep the magnification of algae down, however because they can grow so fast they can also completely cover a pond and block light from reaching other plants. This can result in oxygen deprivation and in return lead to the death of fish, beneficial algae, and other aquatic families. It makes sense then that some duckweed can be considered invasive — for example, Lemna minuta is an invasive species in several European countries.
Duckweed grows best in tropical and temperate zones, although it can grow in a large variety of climates and extreme temperatures. Duckweed isn’t a fan of wind and wave action and is therefore usually found on the surface of fresh or brackish water, ideally at pH levels ranging from 4.5 to 7.5. In these pH levels, ammonium ions are present and can be readily absorbed. Too high a pH causes ammonia to turn to solution form which can be toxic. Water temperatures between 6 and 33 °C in full sunlight or dense shade are optimal. The growth rate of duckweed will increase when the temperature increases, however when 30 °C is hit, growth can begin to slow.
Duckweed has particularly luxurious growth in nutrient-rich districts, like small ponds, swamps, ditches, and even zoos where crocodiles and alligators go (because duckweed can feed on their excrement). Duckweed needs nitrogen, phosphorus, potash, and micronutrients to survive. Food sources can be manure, humus, or compost tea.
In nature, duckweed is found in ponds and lakes. If you bought some duckweed from your local pet store, put it in a basin, and provided it with dechlorinated water and nutrients, you could actually grow some duckweed in your backyard and feed it to your turtle (because duckweed is very high in protein, which we’ll get to in a later section).
However, on a larger scale, duckweed is an ideal feedstock for vertical farming. Duckweed does not require farmable land to grow and so hydroponics can be utilized, which is where crops are grown in water instead of soil. Since the species is so minuscule, you could have layers of duckweed growing in the same footprint. The duckweed would be easier to manage, track, and treat.
Planet Duckweed, a company attempting to commercialize a specific strand of duckweed for food, is doing this very thing in a lab. They use connected trays reliant on gravity for water flow, and skim duckweed from the top of the water. Such a simple system could be built into your basement! Using this prototype, they could produce up to 1.4 million pounds of duckweed per hectare annually, which is a whopping 50 times more than what is derived from corn.
Application For Bioremediation
An incredible property of duckweed is its ability to remove mineral contaminants from wastewaters such as those coming from intensive animal industries or sewage treatment facilities. Duckweed acts as a natural water filter, being efficient at uptaking phosphorus, nitrogen, toxins, and pathogens. On top of that, it can sequester CO2 from the atmosphere. This could be especially valuable in developing countries.
The only downfall here is that the duckweed doesn’t metabolize or break down any of these damaging pollutants, instead holding onto them. Thus, when the duckweed dies, it sinks to the bottom and everything is released. For duckweed to be commercialized for wastewater treatment, the duckweed needs to be harvested and disposed of. According to a paper by BMC Genomics, duckweed can remove up to 78% phosphorus and 85% nitrogen from sewage. This is insane if you think about it!
Perhaps the most exciting application (to me, at least) is duckweed’s promising attributes for a clean biofuel. Biofuels mainly come from first-generation crops like corn, which are often used as food sources. These compete with human consumption and land. What’s useful about duckweed is that it is a second-generation food source, and again as mentioned earlier can be grown in a water-based system, including wastewaters.
To add to these advantages, duckweed would allow growing time to be substantially increased, and five to six times more starch than corn per unit of area generated. Duckweed has a high starch concentration that can reach 75%, which can be manipulated by the conditions and strand. Where biofuels today are questionable in terms of how much they lower greenhouse gases, duckweed would remove carbon dioxide.
Wolffia for Superfood
Duckweed is sometimes called the world’s next superfood, being packed with omega-3 fatty acids and over 45% protein, as well as magnesium, iron, selenium, calcium, manganese, and multiple vitamins. In this case, duckweed usually refers to Wolffia, a tiny bright green fruit that grows no larger than 0.2 mm in diameter. This is already eaten in parts of Southeast Asia and is often referred to as Asian watermeal. Wolffia, resembling the taste of watercress, can easily be added to smoothies or baked goods. If you’re interested in learning more about this, or maybe even trying this superfood yourself, Green Onyx is a leading company in the field!
However, Wolffia isn’t quite here yet. It’s important to keep in mind that duckweed concentrates heavy metals like cadmium and lead, and we don’t want to be consuming these toxins in our diets. We also have to be careful to minimize calcium oxalate, a harmful source of calcium that can be dangerous in large doses. Most leafy vegetables like spinach contain 0.5–1% of oxalate, however duckweed contains 2–4%. This would need to be monitored.
In conclusion, duckweed could be game-changing in numerous ways, and there are some cool emerging companies in the space trying to make it widespread. Here’s an overview of what we learned!
- Duckweed is the fastest growing plant in the world, while also being the smallest
- Duckweed can be a useful animal feed however can also take over aquatic environments and become invasive
- Duckweed grows best in tropical and temperature zones and requires sunlight and nutrients to survive
- Cultivation of duckweed is fairly simple, and vertical farming is a promising method being experimented with
- Duckweed can remove pollutants from wastewater, acting as a natural water filter
- Being a second generation crop, duckweed is a competitive candidate for biofuels
- Containing a variety of nutrients, namely protein, a specific type of duckweed called Wolffia has the potential to be a superfood
Thank you so much for reading this! I’m a 15-year-old passionate about sustainability, and am the author of “Chronicles of Illusions: The Blue Wild”. If you want to see more of my work, connect with me on LinkedIn, Twitter, or subscribe to my monthly newsletter!
Check out these resources if you want to learn more about duckweed!
Nutritional Value of the Duckweed Species of the Genus Wolffia (Lemnaceae) as Human Food
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Growing duckweed for biofuel production: a review - PubMed
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The capacity of duckweed to treat wastewater: ecological considerations for a sound design - PubMed
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