What classification do trickling filters and their various forms fall under?

Trickling filters and their various forms are classified as fixed film treatment processes. This classification is accurate because trickling filters utilize a medium, typically composed of rocks, plastic, or other materials, over which wastewater flows. Microorganisms, primarily bacteria, attach themselves to this medium, forming a biofilm. As the wastewater trickles over the fixed medium, the biofilm metabolizes organic matter and nutrients, effectively treating the wastewater.

The fixed film nature of trickling filters distinguishes them from suspended growth processes, where microorganisms are suspended within the wastewater itself, as seen in activated sludge systems. This design allows trickling filters to provide a large surface area for microbial activity while minimizing the volume of solids in suspension, which is managed differently than in other treatment systems. This makes fixed film treatment processes like trickling filters particularly advantageous in certain applications, ensuring efficient biological treatment of wastewater.