Where is this point on the biological growth curve?
Most industrial systems are designed to operate at the end of stationary to full decline phase growth. This section has the lowest F/M ratios and in theory most of the insoluble/recalcitrant organics are degraded by the microbes into their component soluble fractions.
What can cause a shift from target steady-state?
- Rapid increase (or decrease) in influent soluble organic concentrations (BOD5)
- Hydraulic washout or secondary clarifier problems reduce aeration tank MLVSS
- Shock loadings - a spill of an insouble organic (ex. grease, oils)
- Toxic or quasi-toxic influent (ex. cyanide, phenol, solvents) ~ usually seen in industrial wastewater
- Environmental changes such as pH, temperature, dissolved oxygen, alkalinity especially if change is rapid