What should the wasting rate be in GPM to achieve a MCRT of 15 days given the specified parameters?

To determine the correct wasting rate in gallons per minute (GPM) required to achieve a Mean Cell Residence Time (MCRT) of 15 days, it's essential to understand the relationship between MCRT, the volume of the activated sludge system, and the flow rates.

MCRT is defined as the average time that the microorganisms remain in the treatment system. It is calculated using the formula:

[ \text{MCRT} = \frac{\text{Total mass of mixed liquor suspended solids (MLSS)}}{\text{Wasting rate}} ]

where the wasting rate is how much sludge is removed from the system over a specified time. If the goal is to maintain an MCRT of 15 days, there should be an adequate balance between the inflow, the MLSS concentration, and the rate of waste activated sludge (WAS) removal.

When the wasting rate is at 35 GPM, it suggests a removal of enough biomass that matches the system’s dynamics to sustain a healthy microbial population for the desired retention time. This specific rate may have been calculated or derived based on system characteristics like the size of the aeration tank, the influent characteristics, and existing operational parameters.

In wastewater treatment processes, too low of a