What type of condition would likely indicate high levels of bacteria in a rotating biological contactor?

A reddish brown bio-film is a significant indicator of high levels of bacteria in a rotating biological contactor (RBC). This coloration often suggests the presence of certain types of bacterial colonies that thrive under specific anaerobic or aerobic conditions, which can typically occur when organic loading is high or when the treatment process is not functioning optimally.

In addition to the coloration, reddish brown bio-films can be associated with the accumulation of organic matter, leading to an environment where bacteria multiply rapidly. The change in color indicates that there are active biological processes at work, potentially including the breakdown of waste, but also signals that close monitoring and adjustments may be necessary to prevent negative impacts on the treatment efficiency and overall water quality.

The other conditions described, like a transparent bio-film, dark sludge, or bright color, do not provide the same direct indication of bacterial levels and may rather indicate different states or health of the bio-film or system, such as insufficient bacterial growth or inappropriate environmental conditions. Therefore, the reddish brown coloration is a clear sign of bacterial proliferation that requires attention in the management of wastewater treatment processes.