How does the activated sludge process function?

The activated sludge process is a biological treatment method widely used in municipal wastewater treatment plants. It operates by promoting the growth of microorganisms, primarily bacteria, in an aerated environment. These microorganisms thrive on the organic materials present in the wastewater, effectively consuming and breaking down contaminants.

As the wastewater is aerated, it allows for the introduction of oxygen, which is essential for the aerobic microorganisms to flourish. This biological activity transforms the organic matter into biomass (the microorganisms themselves) and mineralizes it into simpler compounds, thereby purifying the water.

After the treatment process, the mixture of treated wastewater and microorganisms, often referred to as "mixed liquor," is allowed to settle in a secondary clarifier. This separation process allows most of the biomass to settle to the bottom, forming what is called "activated sludge." A portion of this settled sludge is recirculated back into the aeration tank to maintain an adequate population of microorganisms for ongoing treatment, while excess sludge is removed for further processing.

This method is highly effective in reducing biochemical oxygen demand (BOD) and other contaminants, ensuring cleaner effluent is discharged into the environment.