What is a likely cause of a "rotten egg" odor from an aerobic treatment plant?

The presence of a "rotten egg" odor in an aerobic treatment plant is often attributed to hydrogen sulfide gas, which can result from a lack of sufficient aeration. When a mechanical aerator fails, it can compromise the process of aerobic digestion, as the aerator's primary function is to introduce oxygen into the treatment system. This lack of oxygen can lead to anaerobic conditions, where anaerobic bacteria thrive and produce hydrogen sulfide as a byproduct of their metabolic processes. Thus, the failure of the mechanical aerator directly contributes to the conditions that generate that characteristic odor.

In contrast, while chlorinator failure, clogged pumps, and sewage backups can cause unpleasant odors, they typically do not specifically lead to the distinct "rotten egg" smell associated with hydrogen sulfide. Chlorinator issues may lead to a lack of disinfection or chlorine smell, clogged pumps may cause stagnation, and sewage backups often produce a broader foul odor. However, it is the mechanical aerator's role in maintaining aerobic conditions that makes its failure the most likely cause of the detected "rotten egg" scent in this scenario.