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UCT / MUCT — Enhanced Biological P Removal

UCT exists to fix one specific flaw in A²/O: the return sludge carries nitrate straight into the anaerobic zone, where it steals the volatile fatty acids the phosphorus-accumulating organisms need. UCT routes the return sludge through an anoxic zone first. This tool sizes the zones off the nitrification SRT, then shows you exactly how much nitrate load that rerouting saves.

1Duty & water quality

Bio-P performance is driven by the ratio of readily biodegradable COD to phosphorus — as much as by the phosphorus number itself. Keep an eye on the BOD/TP ratio in the results.

2Kinetics — the SRT that nitrification demands

The aerobic SRT is set by how fast nitrifiers grow at your water temperature. Everything else in the reactor follows from it.

3Zone HRTs & recycles

UCT = Anaerobic → Anoxic 1 → Anoxic 2 → Aerobic. Return sludge enters Anoxic 1; the nitrate recycle from the aerobic end enters Anoxic 2. Nothing nitrified reaches the anaerobic zone until it has been denitrified.

Results — reactor & effluent

Total volume
—m³
Total HRT
—h
Effluent TP
—mg/L
ItemValueBasis

4Why UCT — nitrate load on the anaerobic zone

Every kilogram of nitrate entering the anaerobic zone consumes volatile fatty acids that the P-accumulating organisms would otherwise use. This is the entire reason UCT exists.
ItemA²/OUCT

5Nitrogen & phosphorus balance

ItemValueBasis

Oxygen & alkalinity

Two things quietly limit BNR plants: blower capacity, and alkalinity. Nitrification destroys alkalinity; denitrification gives some of it back.
ItemValueBasis

6Instrument schedule

A BNR plant is controlled at its zone boundaries — that is where the instruments belong.
PointInstrumentWhy here

Quote the UCT instruments at factory price

Zone DO, ORP at the anaerobic/anoxic boundaries, MLSS, nitrate and the two recycle flowmeters — all mappable to our catalogue and supplied at the manufacturer's ex-works price (our margin is the export rebate, not a markup on the device).

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Sources & parameter basis

[1]METCALF & EDDY / EPA — BNR configuration: anaerobic 0.5–2 h, anoxic 1–3 h, aerobic 4–12 h; MLSS 2.5–4.5 g/L; RAS 0.5–1.5×; effluent TP achievable biologically 0.5–2 mg/L.
[2]Nitrifier growth μN = 0.47·1.103(T−20)·DO/(1.3+DO) d⁻¹; design SRT = SF·(1/μN) with SF typically 2–6. Aerobic SRT governs nitrification.
[3]Observed yield Yobs = Y/(1 + kd·SRT), kd,T = kd20·1.04(T−20); sludge N content ≈0.10 kg N/kg VSS.
[4]Bio-P sludge carries 3–6 % P (vs 1.5–2 % in a conventional plant); bio-P needs roughly 10 kg BOD per kg P taken up.
[5]Alkalinity: nitrification consumes 7.14 kg CaCO₃/kg NH₃-N; denitrification returns 3.57 kg CaCO₃/kg NO₃-N. Keep ≥70–80 mg/L residual for stable nitrification.
[6]UCT (University of Cape Town) and MUCT: RAS routed to anoxic 1, nitrate recycle to anoxic 2; achievable denitrification ≈ Rir/(1+Rir) limited by available carbon; anoxic-1 nitrate removal ≈85 %.
[7]Oxygen: carbon 0.9, nitrification 4.57, denitrification credit 2.86 kg O₂/kg NO₃-N, biomass 1.42 kg O₂/kg VSS; blower SAE 1.8–2.5 kg O₂/kWh.
Full derivation and worked example: UCT-Bio-P-Calculation-Sheet.md. Compare the A²/O and UCT columns at a high internal recycle — the nitrate load gap is what you are paying the extra anoxic zone for.
© 2026 Nanjing JiuYuHui Environmental Technology Co., Ltd. · jiuyuhub.com · Municipal WWTP design manual — Biological (variant).
⚠ Screening values only. Outputs from this tool are engineering screening estimates. Final equipment sizing, and any construction or permit submission, must be confirmed against the manufacturer’s verified performance curves and the applicable local regulation (e.g., Vietnam QCVN 14 / Indonesia PERMENLHK 68).
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