This ratio is useful as it may explain potential deficiencies in the event of a malfunction, especially in the case of industrial effluents.
Okay, so if we take the example of a nitrogen deficiency, would we then be looking to add a nitrogen source at the treatment plant inlet?
The 100:5:1 ratio is interesting but should be used with caution.
It can indeed serve as a starting point for an assessment of a deficiency in the system (filamentous bacteria, foaming, etc.).
Nevertheless, you have to pay attention to hard COD (total residual that is not assimilated by the bacteria) which can distort the findings.
In a purely aerobic facility (yes, they still exist), the nitrate cannot be assimilated.
Personally, I like to use a BOD:TKN:P indicator.
It's another interesting test you can perform: filter a sample from the sludge tank and measure the presence of nitrogen. The results could help confirm you are dealing with an insufficiency.
You can also use the Mohlman or sludge volume index.
In short, the ratio is an interesting tack to take, but it will deliver incomplete information if used on its own.
So I should just take BOD:TKN:P and not all the carbon and nitrogen pollution?
As for the sludge index, is it useful in indicating an adequate amount or an imbalance in the nutrients? Is there any way you could provide a quick explanation on the sludge index or Mohlman or recommend documentation online? I find it a tricky concept to grasp.