Ace the California Wastewater Treatment Operator Exam 2025 – Dive In and Purify Your Career!

The correct answer is aerobic bacteria. In trickling filters, aerobic bacteria are crucial because they require oxygen to grow and thrive. These bacteria form biofilms on the surfaces of the filtered media, where they break down organic matter present in the wastewater. The biofilm's formation is essential as it allows for the effective metabolic processes that convert waste into less harmful substances.

Trickling filters are designed to facilitate the exposure of wastewater to air, promoting the growth of these aerobic bacteria. As the wastewater trickles over the media, it provides not only a substrate for bacteria to cling to but also oxygen, which is essential for the aerobic metabolism of organic materials.

The other types of bacteria mentioned do not function effectively in trickling filters. Nitrifying bacteria, while important in wastewater treatment, typically thrive in environments where ammonia is present and oxygen levels are high—though in fixed film processes, the emphasis is on biofilm formation with a focus on aerobic conditions. Sulfur-reducing bacteria thrive in anaerobic conditions, where they utilize sulfur instead of oxygen for metabolism. Anaerobic bacteria also prefer environments devoid of oxygen, which is contrary to the operational principles of trickling filters.