Denitrifcation happens when bacteria begin to use nitrate and nitrite as an alternative electron acceptor. This a complex way to say that the bacteria are using the oxygen in nitrate and nitrite, leaving nitrogen gas. If you get denitrification in a treatment basin, it is a good sign and often required for facilities with nitrite/nitrate discharge limits. If you have denitrification in a secondary clarifier, you can have floating solids with TSS carryover into the effluent. So what can you do to prevent denitrification in secondary clarifiers:
- Control bed depths to between 2 - 3 feet by adjusting recycle rates
- Hydraulic residence time in clarifier 2 - 4 hours
- Warm temperatures increase denitrification (high metabolic activity) so problem is usually more pronounced in summer months
- Use a water spray to degas the floating solids - you will see the bubbles breakout and the sludge sink
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