Question

The Penn State Wastewater Treatment Plant experiences high fluctuations in flow rate throughout the year. During football games, the flowrate and BOD concentration entering the treatment plant increases, while in the summer when the majority of students are gone, the flow rate decreases a. Describe what would happen to the treatment efficiency during each of these events (football games and summer). Justify your answer by describing how the F/M ratio and the mean cell residence time (ec) will change during these events. Other than waiting for the flow to return to normal, what action could the operators immediately take in each scenario to help bring the F/M back to its original value? b.

Answer 1

• The F/M ratio is the measurement of food or BOD that is given to the microorganisms in the aeration tank.
• F/M ratio= lbs/ day of food (BOD)/ lbs of MLVSS
• Treatment plants are designed and operated according to the F/M ratio. This ratio varies between 0.2-0.6 in the conventional system and 0.05-0.15 in the aeration system. During football season the F/M ratio is increased which will require more aeration to control the BOD. Whereas during the summer the relative F/M ratio is comparatively lower.
• Additional steps can be taken in aeration to bring down F/m ratio to its original state. Step aeration or extended aeration can be provided to lower the f/m ratio.