Aktiivilietemenetelmät

Aktiivilietemenetelmät, also known as activated sludge processes, are a widely used biological wastewater treatment method. These methods rely on a diverse community of microorganisms, primarily bacteria, to break down organic matter present in wastewater. The process involves aerating wastewater in the presence of these microorganisms, forming an active biomass called activated sludge. This sludge is a flocculent mixture of bacteria, protozoa, and other microorganisms.

In a typical activated sludge system, wastewater enters an aeration tank where it is mixed with the activated sludge and oxygen. The microorganisms consume the dissolved and suspended organic pollutants as a food source, converting them into new biomass and simpler inorganic compounds. After sufficient aeration time, the mixture of treated wastewater and activated sludge is transferred to a settling tank. Here, the activated sludge settles out by gravity, forming a concentrated sludge blanket. A portion of this settled sludge, rich in active microorganisms, is returned to the aeration tank to maintain a sufficient microbial population for treating incoming wastewater. The excess sludge, known as waste activated sludge, is removed from the system for further treatment and disposal. Variations of the activated sludge process exist, each optimized for specific wastewater characteristics and treatment goals, such as extended aeration or sequencing batch reactors.