Lemnaquatic - A simple strategy for freshwater bioremediation

A report by Leon Werner and Johann Liebeton

In addition to nitrogen and potassium, phosphorus is in the form of phosphate, one of the three main components of fertilizers. Concentrated phosphate rock is a finite resource. Phosphorus cannot be replaced or produced artificially like oil. For this reason, it is essential to establish a sustainable phosphate cycle for a growing world population, which reduces the phosphate loss to a minimum.

Our project has the goal of using duckweeds to bind phosphate and nitrate from surface waters and generate biomass. In this way, the environmental problem of eutrophication is alleviated and simultaneously the sedimentation of the phosphate prevented, which would make recycling impossible. An efficient and sustainable use of biomass is fundamental for meeting the desired energy transition. For this reason, the harvested biomass will be used in biogas plants to generate electricity.

Subsequently the digestate will be applied as a fertilizer. We want to prove that duckweeds are suitable recyclers of phosphate and nitrate and that their biomass is a good source of biogas. We also want to determine whether duckweeds can force eutrophication back. Eutrophication is often indicated by mass occurrences (blooms) of cyanobacteria in waterbodies. Therefore, it is highly important for us to be able to easily figure out the titer of cyanobacteria in samples. Fortunately, Motic Europe supports our project “Lemnaquatic” with a microscope so that we can use a hemocytometer for counting the cell titer.

Johann Liebeton counting the cell number of a cyanobacteria culture

with a Motic microscope.

Furthermore, we would like to investigate the metabolism of duckweeds to find out in which kind of molecules phosphate is stored. We think that this information could give us a hint how we could increase the accumulation of phosphate in duckweeds.

So overall, we strive for the establishment of a sustainable phosphate cycle, which is independent of an external source of phosphate.

Microscopic picture of a Lemna minor´s frond surface

The basis of the root of Lemna minor

Roots of Lemna minor at 400X magnification