The collection tank in a sewage treatment plant serves multiple crucial purposes:

· Acting as a buffer during peak flow hours, the collection tank helps maintain a steady flow into the aeration tank, preventing overload and ensuring efficient treatment.

· It functions as a load equalizer, ensuring consistent pollutant concentrations in the feed to the aeration tank, preventing starvation or shock to the microbial population.

· Serving as both a sedimentation tank and a retention area for floating substances, the collection tank helps in the removal of solids and floating debris.

· In smaller plants, the collection tank may double as a storage area for sludge.

When equipped with proper screening, oil traps, and grit removal mechanisms, the collection tank primarily serves as an equalizer. In larger facilities, mixers are often employed to facilitate water movement, leading to the renaming of collection tanks as equalization tanks. However, issues such as mixer jamming prompted a shift away from aeration in collection tanks.

In the past, aeration in collection tanks was common practice, but it was found to negatively impact secondary activated sludge processes by prematurely removing carbon sources. As a result, many plants globally discontinued aeration in collection tanks.

With increasing emphasis on nitrogen and phosphate removal by regulatory bodies like the PCB, maintaining anoxic and anaerobic conditions becomes crucial. Aeration in collection tanks hinders the creation of these conditions necessary for denitrification and phosphate removal, thus undermining treatment efficiency.

Thus, the aeration of collection tanks poses challenges to achieving optimal treatment outcomes, particularly concerning nutrient removal processes. Adhering to current regulatory standards necessitates a re-evaluation of the role of aeration in sewage treatment plant design and operation.