- Low or high temperatures
- High organic loading - 80% of BOD5 typically needs removal before nitrification starts
- Low D.O.
- Sludge age is less than needed to support populations of slower growing AOB/NOB
- Inhibitory compounds (many things can slow or totally inhibit AOB/NOB growth)
What I have learned or seen proof of working during the testing
- AOB cultures are more sensitive to changes in waste makeup & inhibition than NOB
- Changes in influent makeup often cause a drop in AOB/NOB numbers. But without significant inhibition, the AOB/NOB populations will naturally increase - this time lag can be reduced by adding AOB/NOB culture slurry.
- Inhibition is rarely just one single chemical in wastewater. Several inhibitory compounds can combine to inhibit growth.
- Various pre-treatment and in-biological unit options exist to reduce the toxicity and promote AOB/NOB growth. Optimizing the growth environment for nitrifiers is important including removing BOD5, degrading inhibitory compounds (phenol, biocides, surfactants), and keeping environmental factors in the optimal range.