Process Control · Nitrification & Denitrification
Nitrifier Growth Kinetics
Nitrifiers grow far slower than heterotrophs, which is why SRT, not HRT, governs nitrification capacity.
Nitrifier doubling time can run 1–3 days under favorable conditions, versus hours for typical heterotrophic BOD-removing bacteria.
Because of this slow growth, a system needs a long enough SRT to let nitrifiers accumulate faster than they're wasted out, or the population washes out entirely.
This is also why a plant can lose nitrification quickly after a toxic event but takes much longer to recover it — rebuilding a slow-growing population takes real time.
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