Case Study: Effluent Ammonia Reduced by 97.5%

The application of BioRemove AM at an activated sludge plant brought the facility into compliance to meet effluent quality standards. 

Benefits

• Improved plant efficiency by reducing effluent ammonia by 97.5%
• Simplified operations by providing an easy-to-use solution

Background

A chemical plant operates a 7,600 m³/d (2.0 MGD) activated sludge plant designed for nitrogen removal. The influent ammonium (NH₄-N) concentration of the plant ranges from 200-800 ppm. Effluent organic removal and a 30 day sludge age normally supports a healthy nitrifying bacterial population. Nitrate (NO₃-N) removal occurs anoxically in a basin where the return sludge and a portion of the mixed liquor circulate. 

Following a plant upset, effluent NH₄-N levels surpassed 400 ppm causing acute non-compliance with the discharge permit. EnviroZyme was contacted to determine if seeding with BioRemove AM could re-establish nitrification. 

Application

A recommendation to seed the aeration basin with EnviroZyme nitrifiers and raise the basin pH and alkalinity with caustic soda was implemented. Although the basin pH was not responsible for the loss of nitrification, a low basin pH of 6.1-6.5 could have hindered the recovery process. At that pH, it was evident that the alkalinity may not have been sufficient to prevent a nitrate-induced reduction in pH that occurs when nitrification is established. Since nitrification requires a theoretical 7.14 ppm of alkalinity per ppm of NH₄-N oxidized to NO₃-N, a restart could easily drop the pH to below 6.0 and completely inhibit a full recovery. 

Results

BioRemove AM was added to the aeration basin over a ten day period, in addition to raising the mixed liquor pH to 7.7. During this period, the effluent NH₄-N decreased by 97.5% from 397 to 10 ppm.

Effluent ammonium (NH₄-N) and nitrate (NO₃-N)

Effluent ammonium (NH₄-N) and nitrate (NO₃-N). Click or tap to enlarge.

At the same time, effluent NO₃-N increased from 0 to a peak of 135 ppm, then back down to 101 ppm as the denitrification rate responded to increased NO₃-N production. The mixed liquor pH was gradually allowed to drop to the 6.5-7.0 range that had historically supported nitrification, thereby eliminating the need for continuous caustic addition.  

Conclusion

EnviroZyme's biological program was easy to implement and provided significant benefits over other alternatives. BioRemove AM resulted in:

• Lower operating costs
• Improved plant efficiency
• Simplified operations