Curious about global water innovations & regulation updates? Explore Water Channel →
Rispri LabsENGINEERING A CIRCULAR FUTURE

Free tool · Water and wastewater treatment design

MBBR Design Calculator

MBBR media area = BOD load (g/day) ÷ surface area loading rate (g BOD/m²·day). Media volume = area ÷ media specific surface, and reactor volume = media volume ÷ fill fraction. 500 m³/day at 250 mg/L BOD and 7.5 g/m²·day needs about 33 m³ of 500 m²/m³ media in a 67 m³ reactor.

Your inputs

Results update as you type. Example values are filled in.

m³/day
mg/L

After screening and any primary settling.

g BOD/m²·day

5 to 10 for secondary standards (BOD under 30 mg/L), 15 to 20 for a roughing stage.

m²/m³

Typical K1 or K3 type media: 450 to 800 m²/m³. Check the supplier sheet.

%

Keep at or below 67% so media moves freely.

m

How to use this calculator

  1. Enter the average flow and BOD reaching the MBBR.
  2. Choose a surface area loading rate for your effluent target.
  3. Enter the media surface area from the supplier and the fill fraction.
  4. Read media and reactor volume, then split it into reactors in series.

How do you design an MBBR?

Load (kg/day) = Q × BOD ÷ 1,000

Biofilm area (m²) = Load × 1,000 ÷ SALR

Media volume = area ÷ specific surface

Reactor volume = media volume ÷ fill fraction

Loading rates follow Ødegaard (2006) and Metcalf and Eddy. For nitrification design on ammonia loading (about 0.5 to 1 g NH₄-N/m²·day) after BOD is mostly removed.

Worked example

With average flow 500 m³/day, influent bod to mbbr 250 mg/L, surface area loading rate (salr) 7.5 g BOD/m²·day, media protected surface area 500 m²/m³, media fill fraction 50 %, reactor water depth 4 m, number of reactors in series 2:

Total reactor volume: 66.7 m³

The calculator also gives bod load 125 kg/day; biofilm area needed 16,667 m²; media volume 33.3 m³.

Assumptions and limits

  • Loading is on applied BOD at average flow and about 15 to 20 °C. Reduce SALR in cold climates.
  • Does not design for nitrification or nitrogen removal.
  • A clarifier, DAF or tube settler is still needed after the MBBR.

Frequently asked questions

What is the typical HRT of an MBBR?

For BOD removal, MBBR reactors usually have 2 to 6 hours of HRT, much less than extended aeration (16 to 24 hours), because the biofilm holds far more biomass per cubic metre.

What fill percentage is used in MBBR?

Designers typically fill 40 to 60% of reactor volume with media and keep the maximum below about 67% so the media can circulate.

MBBR or SBR for an STP?

MBBR needs less volume and handles load swings well, which suits small footprints and upgrades. SBR does treatment and settling in one tank and is easier to run for nitrogen removal. Both meet CPCB STP norms when designed correctly.

References

  • Ødegaard, H. (2006). Innovations in wastewater treatment: the moving bed biofilm process. Water Science and Technology 53(9)
  • Metcalf and Eddy, Wastewater Engineering: Treatment and Resource Recovery, 5th ed.
  • CPHEEO, Manual on Sewerage and Sewage Treatment Systems (2013)

Built and maintained by the Rispri Labs engineering team. Last updated .