Page 21 - SIMPLIFIED WASTEWATER TREATMENT FUNDAMENTALS\ Advanced Activated Sludge P3

Aeration Contact Time

Summer Season Contact Time Example

In the middle of the summer season, this northern wastewater facility wastewater temperatures approach

25 C (77 F). Under this warm wastewater temperature scenario, the biomass metabolism is thriving. There

is plenty of DO (3.5 mg/L). Summer rains coupled with collection system I&I (Inflow and Infiltration) is

resulting in extremely high daytime peak flows. Process Control dictates a minimum of 2 hours of Contact

Time during peak flow periods:

Factors:

Peak Flow 6.8 MGD Aeration Basin Volume 430,100 gallons

Detention Time Formula

Volume MG x 24 Hours = Hours 0.4301 MG x 24 Hours = 1.52 Hours

Flow MGD 6.8 MGD

Under extreme peak flow conditions, the Aeration Basin is not providing enough Contact Time. Another

Aeration Basin would need to go online, or the Secondary Clarifier RAS flow rate would need to be

reduced.