What is the typical range of Mean Cell Residence Time (MCRT) for most modifications of the activated sludge process?

The typical range of Mean Cell Residence Time (MCRT) for most modifications of the activated sludge process is indeed between 5 to 15 days. MCRT is a crucial parameter in wastewater treatment as it indicates the average time that the microorganisms are retained in the system.

In the activated sludge process, having an MCRT within this range allows for effective treatment as it provides sufficient time for microorganisms to metabolize the organic matter present in the wastewater, thus improving the overall efficiency of the treatment process. A shorter MCRT might not allow enough time for the microbes to break down the pollutants effectively, whereas a significantly longer MCRT could lead to issues such as the growth of less desirable microorganisms and an imbalance in the system.

This range is optimal for balancing the performance of the treatment plant, ensuring that the microorganisms are neither washed out too quickly nor allowed to accumulate excessively, which could destabilize the process.