Let's recap the benefits of plug-flow:
- Good for BOD5 removal followed by ammonia oxidation, denitrification, and even phosphorus removal. Much flexibility in changing aeration, anoxic, anaerobic zone sizes.
- Works well with low BOD5 or degradation of insoluble BOD5 including resistant organics
- High soluble BOD5 loadings near the inlet can create low D.O., promoting filaments
- Susceptibility to shocks - pH, influent temperature, toxic shock loadings (this is why plug flow is much less common in industrial wastewater)