Comparison of nitrification inhibition by metals in batch and continuous flow reactors

Area of Science:

• Environmental microbiology
• Wastewater treatment engineering
• Ecotoxicology

Background:

• Stringent nitrogen discharge limits necessitate rapid assays for nitrification inhibition.
• Nitrification is crucial for removing nitrogen from wastewater.
• Metal contamination in wastewater can disrupt nitrification processes.

Purpose of the Study:

• Evaluate a short-term batch respirometric assay for predicting nitrification inhibition.
• Assess the suitability of the assay for metals like copper (Cu), zinc (Zn), nickel (Ni), and cadmium (Cd).
• Compare inhibition predictions from batch assays to actual responses in continuous flow reactors.

Main Methods:

• Determined linear metal partition coefficients in batch experiments (pH 7.5).
• Utilized a mass-balance model incorporating metal partitioning for continuous flow reactors.
• Evaluated a short-term extant batch respirometric assay.

Main Results:

• Metal partition coefficients varied significantly among Cu, Zn, Ni, and Cd.
• A mass-balance model fit metal concentration profiles in continuous flow reactors.
• Batch assays consistently underestimated nitrification inhibition observed in continuous flow reactors.

Conclusions:

• Short-term batch assays may not accurately predict nitrification inhibition in continuous systems.
• Slow metal internalization kinetics and prolonged exposure in continuous reactors contribute to underestimation.
• Results from batch assays should be interpreted cautiously for continuous flow systems, considering partitioning and uptake.
• Copper's unique mechanism of action may cause greater discrepancies between batch and continuous systems.