How many ways can we purify water?

What is water purification?

In general, this is the cleaning of water from any kind of impurities, such as dirt or microorganisms. Water purification is not a single step, but a process that consists of various sub-steps. Which partial steps are required depends on the impurities in the water. Depending on the type of water, these can be very different.

How can polluted water be treated?


Some dirt can be drawn off in a settling basin before the cleaning process, after it has reached the bottom of the container (sedimentation).

Floating up

Substances such as oils with a normally lower density than water float on the surface and can be drawn off there.

Removal of dangerous microorganisms

Water polluted in this way is usually disinfected with chlorine.

Removal of dissolved substances

Microorganisms are not only a threat to the water; they can also be beneficial in water purification processes by converting harmful substances into harmless ones. This process usually takes a certain amount of time and can only be used for the water that can be purified with the respective microorganisms, mainly bacteria. An example would be the so-called "denitrification", in which bacteria nitrogen compounds such as ammonium (NH4+) via the intermediate stages nitrite (NO2-) (due to the type of bacteria Nitrosomonas) and nitrate (NO3-) (due to the type of bacteria Nitrobacter) into harmless molecular nitrogen (N2) that escapes into the atmosphere.

Physical / chemical cleaning

If biological wastewater treatment with microorganisms is not an option, we use different cleaning methods, which are known as physical or chemical cleaning methods. In chemical cleaning, an additive is often added that causes a chemical reaction so that the impurities can then be removed; these chemical processes to remove contaminants can often be very complex and difficult to understand. Physical cleaning methods are also known as mechanical cleaning stages and include, for example, filtrations.

Process for water pollution control

Click here for more detailed information on the individual stages of water purification.

How are bacteria removed from the water?

Bacteria and other microorganisms are removed with the help of disinfection. Here, substances are added that kill the bacteria. Disinfection can also be carried out with UV light.

You can find more information on disinfection here!

What is aerobic wastewater treatment?

When bacteria are used for wastewater treatment, a distinction is made between aerobic and anaerobic wastewater treatment. Aerobic bacteria, which do the cleaning, need oxygen to live and thus also for the transformation processes that they perform. Often the resulting partial products of aerobic wastewater treatment are carbon dioxide (CO2) and water.

What is Anaerobic Sewage Treatment?

Bacteria that live anaerobically can also be used for wastewater treatment. These bacteria do not need oxygen and can only break down when the oxygen content is low. Instead of this, they need other substances for their processes, e.g. acidogenic Bacteria form organic acids from starches and fats, which are then absorbed by acetogenic Bacteria converted into acetic acid, which of methanogenic Bacteria is converted into methane and carbon dioxide. The methane produced can be used, for example, as biogas and thus as an energy source. The anaerobic breakdown of a substance often requires more steps than the aerobic breakdown and yet often works less satisfactorily. In some processes, the anaerobic degradation is followed by an aerobic degradation for more complete water purification. Normally, however, the wastewater is cleaned aerobically and the resulting sludge is further broken down anaerobically into biogas in rotten eggs.

How are fertilizers removed from the water?

Fertilizers such as phosphate are made by adding another chemical, for example iron (Fe2+ or Fe3+) or aluminum (Al3+) away. This process is called precipitation. The aim is to convert the fertilizer into poorly soluble compounds, which can then be drawn off as sludge or removed by filtration. To remove ammonium or nitrates, see "How can polluted water be cleaned?" (see above) used denitrification. The removal of fertilizer from the water is necessary, among other things, to prevent increased algae formation (eutrophication) in the waters.

To clarify unclear terms, please use our water lexicon.

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