What does an increasing F/M ratio and decreasing MCRT indicate?

An increasing Food-to-Microorganism (F/M) ratio, coupled with a decreasing Mean Cell Residence Time (MCRT), indicates that there is an excess of food (organic matter) being provided to microorganisms in the system compared to the number of microorganisms available to consume it. This situation often leads to more solids being wasted from the system to maintain balance, which diminishes the solids inventory in the treatment process.

In general, a higher F/M ratio signifies that there is more substrate available relative to the biomass, encouraging the growth of microorganisms initially. However, if the MCRT is decreasing concurrently, this indicates that the solids, or biomass, are being removed from the system at a rate faster than they can be replaced or maintained. With less biomass available and potentially more food than the microorganisms can handle, the system can become destabilized, resulting in excessive solids wasting to reduce the overall load on the treatment process.

Thus, this scenario clearly supports the assertion that there is excessive solids wasting leading to a decreased solids inventory within the treatment process.