The capacity of duckweed to treat wastewater: Ecological considerations for a sound design

• Published in: Journal of environmental quality Vol. 32; no. 5; pp. 1583 - 1590
• Main Authors: KÖRNER, Sabine, VERMAAT, Jan E, VEENSTRA, Siemen
• Format: Journal Article
• Language: English
• Published: Madison, WI Crop Science Society of America 01.09.2003; American Society of Agronomy
• Subjects: Algae; Ammonia; Ammonia - toxicity; Applied sciences; Aquatic plants; Araceae - physiology; Biodegradation, Environmental; Biological and medical sciences; Biological treatment of waters; Biotechnology; Environment and pollution; Exact sciences and technology; Floating plants; Fundamental and applied biological sciences. Psychology; General purification processes; Growth rate; Hydrogen-Ion Concentration; Industrial applications and implications. Economical aspects; Lemna; Nitrogen - metabolism; Nutrient removal; Organic matter; Phosphorus - metabolism; Plug flow; Pollution; Waste Disposal, Fluid - methods; Wastewater treatment; Wastewaters; Water Microbiology; Water Pollutants - isolation & purification; Water Purification - methods; Water treatment and pollution; Biodegradation; Microbial activity; Monocotyledones; Organic matter; Lemnaceae; Toxicity; Nitrogen compounds; Review; Operating conditions; Biological purification; Ammonia; Phytotoxicity; Angiospermae; Spermatophyta; Phosphorus compound; Aquatic plant; Waste water purification; Wetland
• ISSN: 0047-2425; 1537-2537
• DOI: 10.2134/jeq2003.1583

Duckweed species are promising macrophytes for use in sustainable wastewater treatment due to their rapid growth, ease of harvest, and feed potential as a protein source. This paper reviews growth rates of different duckweed species on wastewater and ammonia toxicity to duckweed and summarizes insights into the mechanism of organic matter and nutrient removal. Results were gained from laboratory experiments in small, shallow, duckweed-covered semicontinuous batch systems. Growth rates on different types of wastewater vary considerably among different species. Ammonia is toxic for duckweed in both the ionized and un-ionized forms. Duckweed, however, can be used to treat wastewater containing very high total ammonia concentrations as long as certain pH levels are not exceeded. The degradation of organic material is enhanced by duckweed through both additional oxygen supply and additional surface for bacterial growth. The duckweed mat with attached bacteria and algae is, independent of the loading rates, responsible for three-quarters of the total nitrogen (N) and phosphorus (P) loss in very shallow systems. Based on our results we suggest that full-scale pilot plants with duckweed should be shallower than the range encountered in the literature. A harvesting schedule that allows doubling times of 2 to 3.5 d, maintenance of a full coverage, and plug flow conditions are recommended.