How do slow sand filters operate in water treatment?

Slow sand filters function primarily through the development of a biological layer, often referred to as a "schmutzdecke," that forms on the surface of the sand. As water flows through the filter, this layer consists of microorganisms, which play a crucial role in breaking down organics, pathogens, and other particles present in the water.

The mechanism of action relies on both physical and biological processes. The sand itself acts as a physical barrier, trapping larger particles, while the schmutzdecke aids in the biological treatment aspect. As the water continues to pass through, it is naturally clarified and purified, which allows these filters to effectively reduce contaminants over time.

This method of filtration is efficient for treating surface water sources and is widely recognized for its low maintenance and operational costs, as it does not require complex or energy-intensive procedures.