Which of the following mechanisms is a biological action involved in filtration?

The decomposition of organic matter is indeed a crucial biological action involved in filtration. In water treatment processes, biological filtration typically takes advantage of microorganisms that break down organic matter. This process is especially effective in removing not just solid particles but also dissolved organic compounds by metabolizing them into simpler, less harmful substances.

As water passes through a biological filter, bacteria and other microorganisms thrive on the organic material present in the water. They feed on this material, facilitating decomposition, which helps to clarify the water and improve its quality. This biological activity is integral to creating a balanced environment in which beneficial bacteria can flourish, leading to effective removal of impurities.

In contrast, while chemical bonding, physical removal, and displacement may be mechanisms found in other filtration processes, they do not specifically pertain to the biological actions involved in filtration like decomposition does.