Aktiivilietelaitteet

Aktiivilietelaitteet, known in English as activated sludge plants, are a common type of wastewater treatment facility. They are biological treatment systems that utilize microorganisms to remove organic matter and nutrients from sewage. The core of the process involves a tank where wastewater is mixed with a suspension of microorganisms, called activated sludge. Air or oxygen is supplied to the tank to promote the growth and metabolic activity of these aerobic bacteria.

As the wastewater flows through the tank, the microorganisms consume the dissolved and suspended organic pollutants. This biological process converts the organic waste into new microbial cells, carbon dioxide, and water. The activated sludge, rich in these microorganisms, is then separated from the treated water in a settling tank. A portion of this settled sludge is recycled back to the aeration tank to maintain a sufficient population of active microbes, while the excess sludge is removed for further processing and disposal. This recycling mechanism is what gives the process its "activated" name.

Aktiivilietelaitteet are highly effective in reducing biochemical oxygen demand (BOD) and chemical oxygen demand (COD) in wastewater. They can also be adapted to remove nitrogen and phosphorus through the inclusion of specific anoxic and anaerobic zones within the treatment process, leading to nutrient removal. The efficiency of activated sludge plants depends on factors such as the influent wastewater characteristics, the sludge retention time, and the operating conditions of the aeration process.