Tennessee Wastewater Operator Practice Exam

When a fixed film process receives a heavy organic load, which type of bacteria is likely to overgrow?

1. Autotrophic bacteria

2. Heterotrophic bacteria

3. Nitrifying bacteria

4. Pathogenic bacteria

The correct answer is: Heterotrophic bacteria

In a fixed film process, such as a trickling filter or a rotating biological contractor, the system is designed to promote the growth of biofilms made up of microorganisms that can effectively degrade organic matter. When the system experiences a heavy organic load, an increase in available organic material encourages the growth of heterotrophic bacteria. These bacteria thrive on organic substances and play a critical role in the biological treatment of wastewater by breaking down carbon compounds. Heterotrophic bacteria utilize organic carbon as their energy source, and their proliferation is a natural response to abundant organic inputs. This is essential for effective treatment, as these bacteria convert organic pollutants into simpler compounds, which can then be further processed or removed. In contrast, autotrophic bacteria, which primarily derive energy from inorganic substances, do not benefit directly from heavy organic loads. They are more involved in processes such as nitrification, where they can convert ammonia to nitrate but do not significantly increase under conditions of high organic loading. Pathogenic bacteria are not typically associated with the treatment processes; while they may exist in the influent, they do not play a beneficial role in the degradation of organic matter within a fixed film process. Thus, when faced with a heavy organic load, heterotrophic bacteria are the dominant organisms