The bio-film color on a rotating biological contactor undergoing nitrification appears how?

In a rotating biological contactor (RBC) that is undergoing nitrification, the biofilm color typically appears reddish brown to golden. This coloration is largely due to the presence of nitrifying bacteria, such as Nitrosomonas and Nitrobacter. These bacteria are involved in the conversion of ammonia to nitrite and then to nitrate, a key process in the nitrification phase of wastewater treatment.

The reddish-brown hue can be attributed to the accumulation of these bacteria and the pigments they produce, as well as an increase in organic matter present in the biofilm. The golden aspect may come from the clarity and health of the microbial community thriving within the biofilm, indicating effective nitrification. This visual indicator is essential for operators to monitor because it conveys the health and activity of the biological treatment process, which is crucial for effective wastewater management.

The other options may reflect different conditions or processes within wastewater treatment but do not accurately describe the appearance of the biofilm during nitrification in an RBC. For example, dark brown to black typically indicates an anoxic or stagnant condition, while lighter colors like gray or white may suggest less biomass or issues with the microbial community. Therefore, noticing the reddish brown to golden color helps wastewater operators assess the operational effectiveness of