Application of Duckweed in Treating Municipal Wastewater

Report No WSAA 111

May 1996

 

SYNOPSIS

 

Duckweed species, botanical name Lemnaceae, have demonstrated in overseas experiments, a tremendous ability to remove mineral contaminants, primarily nitrogen, phosphorus, potassium, calcium, sodium, magnesium, to mention a few, from wastewaters emanating from municipal Sewage Treatment Works (STW), intensive animal production industries and food processing factories.

 

The objectives of the research program was to take what had been published overseas with regards to duckweed reducing the usually high loadings of mineral nutrients, particularly P, N, K and Na from municipal wastewater and adapt that knowledge to Australian conditions. Many of the research trials conducted overseas used the Lemna minor specie of duckweed, and while it is reported that it grows in Australia, it was not available to the researchers during this research program. The Spirodila and Lemna trisulca species were available to the research team and were used during the trials.

 

Since the research project commenced as Armidale was going into its Autumn and Winter seasons, it was thought that working in a plastic tunnel house environment would be beneficial to the research program. In fact the major variation in the air and water temperatures each day actually worked against the duckweed; the fluctuations were too great and stressed the plant. The results did not match those achieved overseas.

 

The researchers then conducted a series of trials out-of-doors at three Sewage Treatment Works (STW) using a Spirodila specie of duckweed. The results were impressive and confirmed that duckweed has the capability to further polish municipal wastewater in Australia. These trials were conducted during the Summer and Autumn seasons; however more work is required to evaluate how duckweed performs out-of-doors during the winter months in Australia.

 

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

 

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