Aktiivilietemenetelmässä

Aktiivilietemenetelmässä is a Finnish term referring to the activated sludge process, a biological wastewater treatment method. This method is widely used in municipal and industrial wastewater treatment plants to remove organic matter and nutrients. The core of the process involves a mixed microbial population, primarily bacteria, that consume organic pollutants in the wastewater. This microbial community is maintained in a suspended state, hence the term "sludge" or "lietettä".

The activated sludge process typically takes place in an aeration tank. Here, air or oxygen is supplied to the wastewater, providing the necessary conditions for the aerobic microorganisms to thrive and break down pollutants. This aeration also promotes the formation of flocs, which are small clumps of microbial biomass. Following aeration, the mixed liquor, which consists of treated wastewater and activated sludge, flows to a secondary clarifier.

In the clarifier, the activated sludge settles out by gravity. The settled sludge is then separated from the treated effluent. A portion of this settled sludge, known as return activated sludge (RAS), is recycled back to the aeration tank. This recirculation ensures a sufficient concentration of active microorganisms in the system to effectively treat incoming wastewater. The excess sludge, known as waste activated sludge (WAS), is removed from the process for further treatment and disposal. The effectiveness of the activated sludge process relies on maintaining optimal conditions for microbial activity, including sufficient oxygen supply, appropriate sludge age, and control of influent characteristics.