Because of slow growth rates and requirements for a relatively narrow pH & dissolved oxygen range, nitrifiers are some of the most delicate microbes in a wastewater system. Making up only a small percentage of the overall biomass (measured as MLVSS), a loss in viable nitrifiers can cause long run problems in maintaining needed ammonia removal.
I have talked many times about how D.O., alkalinity, pH, and temperature can effect nitrification. This time, I want to mention the most common toxic compounds that even with low concentrations or brief exposure can inhibit ammonia removal.
Major Offender List
Remember that under ideal conditions the surviving nitrifiers can reproduce more rapidly and conceal the influent toxic impact. Under less than ideal conditions (often lower temperatures or low DO), the impact is magnified by low nitrifier reproduction rates.
I have talked many times about how D.O., alkalinity, pH, and temperature can effect nitrification. This time, I want to mention the most common toxic compounds that even with low concentrations or brief exposure can inhibit ammonia removal.
Major Offender List
- Phenol & Aromatic Compounds (BTEX)
- MEK
- Sulfide scavengers with amine groups
- Hydrogen sulfide (reduced sulfur species)
- Cyanide/Cyanates
- Thiourea
- Surfactants/Solvents (many common surfactants inhibit growth)
- Terpene & pinene
- Mercaptan
- Aniline
- Chlorinated organics
- Heavy metals (Cu, Pb, etc)
- EDTA
Remember that under ideal conditions the surviving nitrifiers can reproduce more rapidly and conceal the influent toxic impact. Under less than ideal conditions (often lower temperatures or low DO), the impact is magnified by low nitrifier reproduction rates.
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