Efficient biological waste water treatment
Removal and treatment of municipal and industrial waste water is of great importance to reduce pollution and eutrophication of natural watercourses and is part of a sustainable use of water resources. The waste water chain comprises of the water consumer, the sewer system and the waste water treatment plant where the clean effluent water reaches the surface watercourse.
The municipal waste water on its own is treated in 10,000 waste water treatment plants with an annual energy consumption of 4,400 GWh in Germany (Fricke, 2009), which is 20% of the energy consumption in the municipal sector. Thereof up to 80% are needed for the biological cleaning in the activated sludge basins (Fricke, 2009).
Activated sludge basins are the core of the waste water treatment plants. Carbon and ammonia compounds are degraded in aerated zones by heterotrophic bacteria under usage of oxygen. Sufficient supply of oxygen to the microorganisms is performed by gas dispersion in the basins. The gas dispersion also assures mixing of the multiphase fluid, i.e. reduction of concentration gradients and suspension of the sludge. Therefore, special diffusers are applied at the bottom of the basins which have an enormous energy demand.
Often additional stirring units are applied to support mixing of the activated sludge and gas dispersion, which need additional energy. Therefore, the process performance and the energy efficiency of waste water treatment plants are mainly determined by the activated sludge process.
- Fricke, K.
Energieeffizienz kommunaler Kläranlagen
Umweltbundesamt, Dessau-Roßlau (2009)