What type of microorganisms tend to dominate in high F:M conditions with young sludge?

In high food-to-microorganism (F:M) ratio conditions with young sludge, the environment is typically characterized by an abundance of readily available organic matter that microorganisms utilize for growth. Under these conditions, flagellates and free-swimmers often thrive as they are well-adapted to exploit the rich nutrient supply.

Flagellates are motile organisms that can move freely in the liquid phase, helping them efficiently capture food sources and respond to their environment. Their presence indicates active biological processes and a dynamic microbial community that can quickly adapt to changes in food availability. The young sludge, which has a lower concentration of inorganic solids and a more significant proportion of living microorganisms, also supports the growth of these types of organisms.

In contrast, sessile bacteria tend to attach to surfaces and are more common in stable biofilm conditions rather than in the mobile and nutrient-rich context of young sludge. Filamentous bacteria often arise in situations where nutrients may be limited or when environmental conditions lead to lower efficiency in biomass processing, which is not typically the case in high F:M scenarios. Protozoa, while they do play a role in the ecosystem of wastewater treatment, particularly in consuming bacteria, are often more prevalent in mature sludge where a balance of microbial communities