Wastewater New York State Practice Exam

A "rotten egg" odor near a trickling filter generally indicates what?

1. Excessive aerobic activity

2. Septic conditions in the filter

3. Anaerobic conditions within the filter

4. Increased organic load

The correct answer is: Anaerobic conditions within the filter

The presence of a "rotten egg" odor, commonly associated with hydrogen sulfide gas, typically indicates anaerobic conditions within the filter. Anaerobic bacteria thrive in environments lacking oxygen and can produce this compound during the breakdown of organic matter. In a trickling filter, if anaerobic conditions develop, the odor suggests that the wastewater is not being adequately aerated, leading to the unfavorable chemical processes that occur in low-oxygen environments. When the flow of wastewater is insufficient or when the filter media is overloaded, it can promote these low-oxygen zones, allowing the anaerobic decomposition of waste and resulting in the characteristic smell of rotten eggs. Identifying this odor is crucial for operators because it signals potential operational issues that may require intervention, such as increasing aeration or adjusting the load to ensure that aerobic conditions are maintained, which are far more conducive to effective treatment.