SBR Cycle Time Calculator
A sequencing batch reactor lives or dies by its cycle schedule. Enter your phase times and cycles per day to check the fit, the volume treated per cycle, and the decant rate.
SBR Cycle Check
| Item | Value |
|---|
How the calculation works
Formulas
Total cycle time = fill + react + settle + decant + idle (min)
Time available per cycle = 1,440 / cycles per day (min)
Slack = available – total cycle time (min)
Volume per cycle = daily flow / cycles per day
Decant rate = volume per cycle / decant time
Total cycle time = fill + react + settle + decant + idle (min)
Time available per cycle = 1,440 / cycles per day (min)
Slack = available – total cycle time (min)
Volume per cycle = daily flow / cycles per day
Decant rate = volume per cycle / decant time
| Phase | Typical duration |
|---|---|
| Fill | 25% of cycle |
| React | 35% of cycle |
| Settle | 20% of cycle |
| Decant | 15% of cycle |
| Idle | 5% of cycle |
Notes & limitations
Phase splits vary widely by treatment goal — nutrient-removal SBRs add anoxic fill or post-anoxic react steps (Metcalf & Eddy). The typical percentages above are starting points for carbonaceous BOD removal, not design values.
- The cycle must fit inside 1,440 / cycles minutes. If it does not, the schedule is impossible — cut a phase or run fewer cycles.
- Decant rate sets the decanter/weir sizing: too fast and you pull solids over the weir. Keep the decant velocity within the equipment rating.
- Volume per cycle assumes the full daily flow splits evenly across cycles; peak-hour equalization upstream changes the real per-cycle volume.
- Settle time depends on sludge settleability (SVI). Poor settling needs longer settle and decant phases — verify against clarifier-style settling tests.
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