Wastewater New York State Practice Exam

What odor indicates the presence of anaerobic conditions in a trickling filter?

1. Ammonia

2. Rotten egg

3. Fishy

4. Muddy

The correct answer is: Rotten egg

The presence of anaerobic conditions in a trickling filter is indicated by the odor of rotten eggs, which is primarily due to hydrogen sulfide (H2S) gas. This gas is produced when sulfate-reducing bacteria thrive in environments lacking oxygen, breaking down organic material. In anaerobic conditions, these bacteria become more active, leading to the formation of hydrogen sulfide, which has a distinct and strong odor reminiscent of rotten eggs. In contrast, odors like ammonia may occur in both aerobic and anaerobic conditions, but they do not specifically indicate anaerobic processes. Fishy odors can be caused by various factors in wastewater treatment but are not as directly linked to anaerobic activity as hydrogen sulfide. The muddy smell typically relates to sediment or organic material but does not specifically signify anaerobic conditions either. Thus, the identification of a rotten egg odor is a clear indicator of anaerobic conditions in a trickling filter system.