Duckweed is a tiny, free-floating aquatic plant found globally in still or slow-moving freshwater bodies. Belonging to the Lemnaceae family, it is sometimes called water lens or water meal. This plant is considered the fastest-growing higher plant on Earth, capable of doubling its biomass in as little as 16 to 24 hours under ideal conditions. Its rapid reproduction and high biomass accumulation position duckweed as a versatile resource for environmental restoration, sustainable food, and fuel production.
Environmental Cleanup and Water Treatment
Duckweed excels in cleaning contaminated water through a natural process called phytoremediation. The plant rapidly absorbs excess nutrients like nitrogen and phosphorus from wastewater, sewage, and agricultural runoff. This nutrient uptake is crucial for preventing eutrophication, which leads to harmful algal blooms and oxygen depletion.
Studies show duckweed can remove up to 99% of phosphorus and 50 to 60% of total nitrogen from domestic wastewater. In its biomass, duckweed can accumulate significant amounts of nutrients, with estimates suggesting up to 9.1 tons of nitrogen and 0.8 tons of phosphorus per hectare per year. Duckweed also demonstrates a capacity to accumulate heavy metals, including arsenic, copper, cadmium, and lead, making it suitable for purifying industrial wastewater streams.
High-Protein Feed for Livestock and Aquaculture
Duckweed offers a sustainable and protein-rich alternative to conventional animal feedstuffs like soy and fish meal. Its crude protein content typically ranges from 20 to 45% of its dry weight, sometimes reaching 51%. This protein is of high quality, containing a well-balanced spectrum of essential amino acids comparable to animal protein.
The plant is utilized in aquaculture and livestock farming as a readily available feed supplement. In aquaculture, species like tilapia and carp efficiently convert duckweed into live weight. For poultry and cattle, duckweed can be incorporated into diets to replace a portion of more expensive protein sources. Its ease of cultivation on nutrient-rich water, such as animal waste lagoons, enhances its viability as a cost-effective and local feed source.
Duckweed as a Novel Human Food Source
Certain duckweed species, particularly Wolffia globosa, are gaining global attention as a novel human food ingredient, often marketed as “watermeal.” This tiny plant delivers a high-quality protein source, with all nine essential amino acids present in a profile comparable to egg protein. The high protein content and low fat content make it an appealing option for plant-based diets.
Duckweed is one of the few plant-based foods that contains a bioactive form of Vitamin B12. The plant also contains important micronutrients, including high levels of iron, calcium, fiber, and Omega-3 fatty acids. While modern applications include processing it into protein powders for smoothies or mixing it into snacks, species of Wolffia have been consumed traditionally in some Southeast Asian countries for centuries.
Generating Energy Through Biomass
Duckweed is a promising feedstock for renewable energy production. As a biomass crop, it can be converted into several forms of biofuel, primarily bioethanol and biogas. The plant’s ability to accumulate significant amounts of starch, particularly in species like Spirodela polyrhiza and Lemna minor, is key for bioethanol production.
Through selective cultivation, the starch content of the dried biomass can reach up to 45%, with a high conversion efficiency to fuel-grade ethanol. Alternatively, duckweed biomass can be subjected to anaerobic digestion to produce biogas, which is primarily methane. Coupling this energy generation with wastewater treatment allows for a sustainable “waste-to-fuel” system, maximizing resource recovery.