Applicationof Duckweed in Treating Municipal Wastewater

ReportNo WSAA 111

May 1996

SYNOPSIS

Duckweedspecies, botanical name Lemnaceae,have demonstrated in overseas experiments, a tremendous ability to removemineral contaminants, primarily nitrogen, phosphorus, potassium, calcium,sodium, magnesium, to mention a few, from wastewaters emanating from municipalSewage Treatment Works (STW), intensive animal production industries and foodprocessing factories.

Theobjectives of the research program was to take what had been published overseaswith regards to duckweed reducing the usually high loadings of mineralnutrients, particularly P, N, K and Na from municipal wastewater and adapt thatknowledge to Australian conditions. Many of the research trials conductedoverseas used the Lemna minor specieof duckweed, and while it is reported that it grows in Australia, it was notavailable to the researchers during this research program. The Spirodila and Lemna trisulca species were available to the research team and wereused during the trials.

Sincethe research project commenced as Armidale was going into its Autumn and Winterseasons, it was thought that working in a plastic tunnel house environmentwould be beneficial to the research program. In fact the major variation in theair and water temperatures each day actually worked against the duckweed; thefluctuations were too great and stressed the plant. The results did not matchthose achieved overseas.

Theresearchers then conducted a series of trials out-of-doors at three SewageTreatment Works (STW) using a Spirodilaspecie of duckweed. The results were impressive and confirmed that duckweed hasthe capability to further polish municipal wastewater in Australia. Thesetrials were conducted during the Summer and Autumn seasons; however more workis required to evaluate how duckweed performs out-of-doors during the wintermonths in Australia.

Therewere several trials of growing duckweed on coal mine wastewater to determine ifthe plant would have a major impact on lowering the conductivity level of thewastewater. Effluent from municipal STW was used as the nutrient for theduckweed’s growth. The researchers found that the duckweed can tolerate themine wastewater, but cannot uptake the huge quantities of salts required by themining companies.

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