Which of the following processes primarily removes organic matter in secondary treatment?

The process that primarily removes organic matter in secondary treatment is biological processes. During secondary treatment, wastewater is subjected to biological processes that utilize microorganisms, such as bacteria, to degrade and consume organic matter effectively. This method is crucial because it breaks down the organic pollutants present in the wastewater, converting them into biomass and other byproducts.

Biological treatment methods can include activated sludge systems, trickling filters, or biofilm reactors, among others, all of which foster conditions for microorganisms to thrive and perform their function of organic matter degradation.

In contrast, the other processes mentioned serve different roles in wastewater treatment. For instance, filtration typically involves the removal of solid particles and debris rather than the organic matter itself. Chemical reactions may play a role in treating specific contaminants but are not the primary mode for the removal of organic matter in secondary treatment. Physical sedimentation is primarily focused on separating solids from water by gravity, which although part of the overall process, does not target the breakdown of organic material specifically. Thus, biological processes are essential in effectively removing organic matter during secondary treatment.