How does a trickling filter system work?

A trickling filter system works by utilizing a physical process where wastewater is distributed over a bed of media, such as rocks or plastic, to promote the growth of biofilm. As the wastewater flows over this medium, microorganisms in the biofilm absorb and break down organic matter and pollutants present in the water. The design of the trickling filter allows for adequate aeration, enhancing the activity of the microorganisms as they digest the contaminants. This biological treatment process effectively reduces the concentration of harmful substances in the wastewater, leading to cleaner effluent being produced.

The choice involving boiling water focuses on a thermal process that does not address the biological treatment aspect crucial to sewage treatment. Chemical reactions imply a different treatment method that typically involves the addition of chemicals rather than relying on natural biological processes. The option mentioning a rotating drum describes a mechanism that is not characteristic of trickling filters, as they primarily depend on passive flow rather than mechanical mixing. Thus, the process of spreading wastewater over a medium for biofilm development is the defining characteristic that showcases how trickling filter systems function effectively in wastewater treatment.