Biological wastewater treatment: how does it work and which processes are there?

In addition to the mechanical wastewater treatment, in which solids are separated from the wastewater, the main purification of the wastewater takes place in a biological stage. How this works, what procedures exist and what conditions are needed is explained here.

How does the biological treatment work?

In biological purification, microorganisms convert the organic components contained in the wastewater. The wastes in the wastewater serve the microorganisms as food.

At the same time, many chemical substances are transformed into other valuable compounds. The end products are certain inorganic compounds and biomass.

The way of application differs depending on the procedure.

Method for biological wastewater treatment

Most commonly used is the so-called activated sludge process, which is also used in SBR plants.

Trickling filter systems represent another application that is rarely used in small wastewater treatment plants. For fixed bed plants, the same applies, they are also little used in small sewage treatment plants.

Slightly more widespread have plant sewage treatment plants. They are very well suited for smaller sized sewage treatment plants and also offer cost advantages. Also waste water ponds are a biological cleaning process.

Conditions for the smooth running

  • sufficient mechanical pre-cleaning and separation of solids
  • adequate oxygen supply during aerobic reaction processes
  • functioning air seal in anaerobic processes
  • Protection of microorganisms against toxins and pollutants (such as heavy metals)
  • sufficient nutrient supply for the microorganisms (through regular wastewater discharge)

Tips & Tricks

Part of the resulting surplus sludge is deducted in the course of the secondary clarification and must be regularly disposed of as the primary sludge from the pre-cleaning fee.

Video Board: How Do Wastewater Treatment Plants Work?