Economic considerations in wastewater treatment with duckweed for effluent and nitrogen renovation

Duckweed is one of the floating aquatic macrophytes with a preference for ammonia uptake. The ammonia is assimilated into valuable nitrogen compounds that can subsequently be used for animal feed or agricultural fertilization. Outdoor experiments were conducted in shallow miniponds (20 and 30 cm deep) to evaluate the performance of the duckweed species, Lemna gibba, as a stripper for domestic wastewater. The results indicate that under adequate operational conditions the quality of accepted secondary effluents meets irrigation reuse criteria. The annual yield (dry matter) of duckweed, which is harvested two to three times a week, is anticipated to be about 55 ton/ha, with a protein content close to 30%. The benefit of the additional byproduct means a reduction in wastewater expenses in the range of $0.020 to $0.050/m³.