SBR Reactor Sizing Calculator
Size your Sequencing Batch Reactor in minutes. Enter flow, BOD, COD, and TSS to get reactor volume, number of tanks, complete cycle breakdown, aeration hours, and sludge production — based on standard SBR design parameters.
Enter Wastewater Parameters
How the SBR Sizing Calculator Works
This calculator uses the sludge retention time (SRT) method — the same approach used by process engineers for preliminary SBR design. The key equation is:
Where Yobs = Y / (1 + kd × SRT) is the observed net yield after accounting for endogenous decay. The calculator applies an SRT of 18 days (mid-range of the 15–20 day design window), MLSS of 3,500 mg/L, and a VSS/TSS ratio of 0.80 — consistent with standard activated sludge and SBR design practice.
Understanding SBR Cycle Phases
An SBR operates in four distinct phases within each cycle:
Fill (25% of cycle)
Influent wastewater enters the reactor. Aeration may be switched on during the latter half of fill to begin biological oxidation.
React / Aeration (45% of cycle)
The main treatment phase. Aeration drives biological BOD and COD removal. Anoxic periods within this phase enable nitrification-denitrification for nitrogen removal.
Settle (20% of cycle)
Aeration stops. Biomass settles to the bottom under gravity. Clear treated supernatant rises to the top. This phase requires controlled conditions — no disturbance.
Decant (10% of cycle)
Treated supernatant is withdrawn from the top using a floating or fixed decanter. Waste sludge (excess biomass) may also be removed during or after decant.
When to Choose SBR Over MBBR or ASP
SBR is the right choice in several specific scenarios. It excels for batch-nature effluent generation — common in breweries, beverage plants, and dairy operations that generate large volumes during production shifts and minimal effluent at other times. The SBR's fill phase naturally accommodates this variability.
SBR also delivers excellent combined BOD + nitrogen removal in a single reactor without separate anoxic tanks — making it space-efficient for nitrogen compliance. If your discharge standard requires nitrogen removal (CPCB standard for inland surface water bodies), SBR can often achieve this without adding a separate anoxic zone.
For comparison, consider our MBBR Sizing Calculator if your plant has existing tanks to retrofit, or requires continuous-flow operation with minimal controls. For higher effluent quality requirements (BOD <5 mg/L, TSS <2 mg/L), see our MBR Sizing Calculator.
SBR Design Parameters: What the Standards Say
| Parameter | Typical Range | This Calculator |
|---|---|---|
| MLSS | 3,000–4,000 mg/L | 3,500 mg/L |
| SRT | 15–20 days | 18 days |
| Volumetric Exchange Ratio | 0.3–0.5 | 0.4 |
| VSS/TSS ratio | 0.7–0.85 | 0.80 |
| Yield coefficient (Y) | 0.4–0.6 g VSS/g BOD | 0.5 |
| Decay rate (kd) | 0.04–0.08 /day | 0.06 /day |
| Min. tanks for continuous flow | 2–4 | 2 (<100 KLD), 3 (100–500 KLD), 4 (>500 KLD) |
SBR in Indian Industrial Practice
SBR has gained significant traction in Indian industrial wastewater treatment since the early 2000s. The technology is particularly popular in the food and dairy sectors, where CPCB consent conditions typically require BOD <30 mg/L and COD <250 mg/L for inland surface water discharge. Well-operated SBR systems routinely achieve BOD <20 mg/L and COD <150 mg/L — comfortably within CPCB norms.
The main advantage of SBR in the Indian context is its tolerance for variable and intermittent flow — critical for food processing plants that run 2-shift operations. The programmable logic controller (PLC) manages all cycle phases automatically, reducing dependence on skilled operators and enabling remote monitoring.
Spans Envirotech has designed and commissioned SBR systems across F&B, dairy, and pharmaceutical industries in India and Africa. Learn more about our food & beverage wastewater treatment solutions.
Frequently Asked Questions
How do you calculate SBR reactor volume?
SBR reactor volume is calculated using: V = Q × SRT × Y_obs × BOD_removed / (MLSS × VSS fraction). Where Y_obs = Y / (1 + kd × SRT). For a 100 KLD plant with BOD 500 mg/L (target 30 mg/L), SRT 18 days, Y 0.5, kd 0.06, MLSS 3500 mg/L, the reactor volume is approximately 100 × 18 × 0.35 × 470 / (3500 × 0.80) ≈ 106 m³ total, split across 2 tanks.
What MLSS should be designed for in an SBR?
SBR systems are typically designed for MLSS of 3,000–4,000 mg/L. Lower than 3,000 mg/L results in a larger reactor volume. Higher than 4,000 mg/L can compromise settling in the settle phase, leading to poor effluent quality. 3,500 mg/L is a safe design point for most industrial wastewaters.
Can SBR handle high-strength wastewater from food processing?
Yes. SBR handles high-strength food processing wastewater (BOD 500–2,000 mg/L) effectively. The key is ensuring adequate SRT (15–20 days) to maintain a sufficient biomass concentration and prevent washout. For BOD above 1,500 mg/L, pre-treatment (equalization, screening, DAF) is recommended before the SBR.
What is the difference between SBR and MBBR?
SBR uses suspended growth (free-floating biomass in the reactor), while MBBR uses attached growth (biofilm on plastic media). SBR has a simpler structure (no separate clarifier needed) but requires precise timing controls and minimum 2 tanks. MBBR is more tolerant of shock loads and can be retrofitted into existing tanks, but needs a downstream clarifier. For the same flow, MBBR often has a smaller footprint.
How much power does an SBR use?
SBR power consumption is dominated by aeration blowers — typically 0.8–1.5 kWh per kg BOD removed, or roughly 0.3–0.7 kWh/m³ of wastewater treated. For a 100 KLD SBR treating BOD 500 mg/L to 30 mg/L, daily power consumption is approximately 150–300 kWh/day.
Ready to Move to Detailed Design?
This calculator gives you planning-level estimates. For a complete SBR design package with P&ID, equipment list, civil drawings, and project cost — our team is ready.