Phosphates and fish mortality
The phosphorus in our waters must be removed from the water in order to inhibit plant growth (algae). During their growth, algae are useful as suppliers of oxygen. But when they die, sink to the bottom of the lake and decompose, they need a lot of oxygen. This is extracted from the water. This initially kills the fish. At a later stage, the water becomes cloudy due to a lack of oxygen and starts to smell bad.
Before the water is returned to nature, phosphorus must be eliminated in order to promote oxygenation of the water, allow fish to thrive and achieve good water quality.
Process for phosphate elimination
In principle, phosphates could be removed from the water biologically by cultivating phosphorus-consuming flora and skimming or filtering it off as soon as it has done its job. However, this requires large tanks and the process has proven to be unstable in practice. Removing the phosphates chemically is both environmentally friendly and reliable. A chemical substance (precipitant) is dosed into the wastewater treatment plants or sewage treatment plants, which forms an insoluble precipitate with the phosphate. This mixes with the other solids in the wastewater and can thus be removed. Proven precipitants are water-soluble salts of iron or aluminium. Both elements also occur in nature.