Florida Wastewater Practice Test

In the contact stabilization process, what do bacteria perform in the stabilization (re-aeration) tank?

1. Oxidation of pollutants

2. Absorption and digestion of the waste material

3. Filtration of solids

4. Coagulation of particles

The correct answer is: Absorption and digestion of the waste material

In the contact stabilization process, the primary function of bacteria in the stabilization or re-aeration tank is the absorption and digestion of waste material. During this phase, bacteria utilize organic pollutants as their food source, breaking them down through metabolic processes. This biological activity is critical in reducing the concentration of organic matter present in the wastewater. Absorption refers to the uptake of soluble substances by the bacterial cells, while digestion involves the enzymatic breakdown of complex organic molecules into simpler compounds that bacteria can metabolize. This process not only helps to stabilize the wastewater by reducing its biochemical oxygen demand (BOD) but also contributes to overall nutrient removal, which is essential for maintaining water quality standards. The other options focus on processes that occur outside the primary function of bacteria in the stabilization tank. While oxidation of pollutants is a part of bacterial metabolism, stating it in this context can be misleading since it doesn't encompass the full scope of what absorption and digestion represent. Filtration of solids and coagulation of particles involve physical or chemical processes rather than the biological activity of bacteria, which further clarifies why absorption and digestion is the correct choice in this case.