What type of organisms would be associated with very clear plant effluent and low BOD?

Very clear plant effluent and low biochemical oxygen demand (BOD) are indicative of a well-functioning wastewater treatment process, particularly in the biological treatment phases like activated sludge systems. Stalked ciliates are single-celled organisms that thrive in aerobic conditions and are commonly found in healthy activated sludge systems. Their presence signifies an active and functional microbial community that is effectively breaking down organic matter.

Stalked ciliates are known for their ability to consume bacteria and particulate organic material while maintaining clear water. Their growth usually indicates a balance in the ecosystem, which corresponds with low BOD levels as they efficiently process available substrates, reducing the amount of organic matter that contributes to BOD.

In contrast, filamentous bacteria can contribute to bulking in activated sludge systems, muddling the effluent quality and leading to higher BOD levels. Sludge worms are typically found in sludge digesters and may not play a significant role in clarifying effluents. Anaerobic bacteria, while important in the treatment of sludge and organic material under low oxygen conditions, do not generally correlate with clear effluent or low BOD because they do not function optimally in aerated systems where clarity is an objective. Thus, stalked ciliates best represent the