What is a sign of healthy biomass on rotating biological contactors?

• A. Brown, thin, even.
• B. Green and thick.
• C. Black and crusty.
• D. White and fluffy or floating.

Answer: (A)

Biomass health on rotating biological contactors is shown by a brown, thin, and even film on the media. The brown color reflects a mature, balanced community of microorganisms actively treating the wastewater. A film that stays thin and evenly distributed allows oxygen to diffuse effectively to the microbes and ensures substrate contact around the media as it turns, supporting stable, efficient treatment. If you see green and thick growth, that points to algae overgrowth or excessive biofilm buildup, which can impede oxygen transfer and waste processing. A black and crusty film suggests fouling or dead biomass with mineral deposits, reducing treatment performance. White and fluffy or floating material signals sloughing, foaming, or poorly attached biomass, indicating instability. So, brown, thin, and even is the best sign of healthy, functioning biomass on RBCs.