- Need for high levels of dissolved oxgyen
- Consumption of alkalinity
- Relatively slow growth
- Susceptibility to numerous toxic chemicals
When it comes to nitrate/nitrite removal the following conditions are needed:
- Effective 0 dissolved oxygen - anoxic conditions
- A source of soluble "food" ~ often called BOD. Note the solubility factor, as using nitrate as electron acceptor does not allow for rapid metabolism on complex or insoluble compounds such as fats, oils, or long chain hydrocarbons.
Denitrification can also be a problem when there is excessive nitrate in the secondary clarifier. If the solids are held in the clarifier too long (usually >3 hours) - the bacteria can use the nitrate to degrade adsorbed organics. The sludge then floats to the top of the clarifier and can carry over the weir. In this case the most often used solution is to increase recycle rates which lowers residence time in the clarifier.