Environment

Saving lake waters through oxygenation by use of electrodes

Lake waters could be soon be saved from the problem of oxygen depletion through the oxygenation process by the use of electrodes.

The problem of oxygen depletion and algae is a common phenomenon across lake waters globally. This happens as a result of discharging wastewater with a high phosphorus content directly into the lake waters.

Human activities and industrialization lead to a high concentration of nutrients in lakes. For example, water runoff from agricultural land or specific effluent discharges. These activities contribute to a gradual (or severe) change to a water body status and result in pollution in rivers and eutrophication in lakes.

Oxygen depletion occurs in aquatic environments when dissolved oxygen (DO; molecular oxygen dissolved in the water) becomes reduced in concentration to a point where it becomes damaging to aquatic life in the water ecosystem.

Dissolved oxygen (DO) is important to living aquatic organisms. The amount of dissolved oxygen in a stream or lake can determine the quality of water. As a result of pollution, the sediment at the bottom of water bodies has oxygen deficiency for bacteria to break down dead plants, fish, and algae, thus making the lakes often appear both murky and smelly.

However, the problem of oxygen depletion could now be solved as a pilot project in Lake Søllerød has successfully used electrodes to oxygenate the lake bed. 

Researchers from the DTU Environment come up with the idea of lake oxygenation using electrodes. DTU Environment is one of the largest university departments specializing in water, environmental engineering, and sustainability in Europe.

Many different ways of oxygenating the bottom of lakes have been trialed. According to Professor Stefan Trapp from DTU Environment, who came up with the idea for the new promising method said the method is simple and inexpensive

“Our new method is both simple and inexpensive. We’ve tested it first in the laboratory and subsequently in a pilot project in Lake Søllerød, and with very promising results; in the form of a reduction of the phosphorus content in the deepest water strata of up to 94 percent.” 

“In practice, the method consists of lowering two steel meshes into the top and bottom of the lake, respectively. The two meshes are connected by a wire and form a kind of electric battery. As they break down dead plants and fish, the bacteria at the bottom of the lake release electrons that are caught by the steel mesh and travel to the surface mesh, where oxygen is present and can absorb the electrons,” explains Karl Haxthausen, DTU Environment, who has been responsible for the practical part of the work.

“In this way, the bacteria can break down the dead organic matter as if oxygen was present. And in fact, the whole process takes place without producing unwanted methane. The removal of electrons also changes the chemistry at the bottom of the lake, causing the phosphorus to bind to the sediment and thus resulting in its immobilization,” says Karl Haxthausen.

The encapsulation of the phosphorus is a notable result of the new method as there is more phosphorus in a single centimetre of the sediment on the bottom than in 10-metre deep water.

The pilot project with the two steel meshes in Lake Søllerød started in summer 2019 and ends now.

“Our results are so promising that we would like to conduct a large demonstration trial, where we not only use a couple of small 4 x 4-metre meshes but instead test our method on an entire lake—for example an area of 100 x 100 metres,” says Stefan Trapp.

The outcome of this pilot project could be used as a new approach to save lake waters from future pollution. It could also be extended to marine water ecosystems and other water bodies experiencing oxygen depletion.

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