Calculator Inputs
Example Data Table
| Scenario | Flow m³/day | MLSS mg/L | Flux LMH | SRT days | Typical Use |
|---|---|---|---|---|---|
| Small municipal plant | 1,000 | 8,000 | 16 | 20 | Compact wastewater upgrade |
| Medium reuse facility | 5,000 | 9,500 | 18 | 25 | High quality reuse water |
| Industrial pretreatment | 2,500 | 10,000 | 14 | 30 | Variable organic load control |
| Peak constrained site | 8,000 | 9,000 | 20 | 22 | Limited footprint project |
Formula Used
How to Use This Calculator
Enter the average wastewater flow and peak factor first. These values define hydraulic loading. Add the required HRT, MLSS, MLVSS percentage, and SRT. Then enter organic and nitrogen concentrations. These values define treatment loading and oxygen demand.
Next, enter membrane design values. Use the design flux for normal operation. Use peak flux for short duration high flow checks. Add module area and redundancy to estimate installed membrane modules. Finally, enter aeration data, tank depth, and oxygen transfer efficiency.
Press the calculate button. The result will show tank volume, HRT, membrane area, module count, sludge wasting, oxygen demand, alkalinity need, and air flow. Use CSV or PDF export for design notes, review records, or engineering worksheets.
Membrane Bioreactor Design Guide
What an MBR Design Checks
A membrane bioreactor combines biological treatment with membrane separation. The biology removes organic matter and nutrients. The membrane retains solids inside the reactor. This allows higher mixed liquor levels than many conventional systems. It also reduces clarifier dependence. A design must balance tank volume, solids age, oxygen demand, membrane flux, and air scouring.
Hydraulic and Biological Sizing
The first step is flow selection. Average flow controls normal loading. Peak flow controls short term membrane demand. HRT sets the liquid volume. SRT controls biomass age and sludge wasting. Higher SRT can improve nitrification. It can also reduce observed sludge yield. Very high SRT may increase oxygen demand and viscosity. The calculator shows both HRT and F/M ratio. These values help judge process stability.
Membrane Area and Flux
Flux is the permeate rate per square meter of membrane. Lower flux gives more membrane area. It can reduce fouling stress. Higher flux reduces capital area. It may increase cleaning frequency. The calculator compares average and peak area requirements. It then adds redundancy and rounds modules upward. This gives a more practical installed area. Actual flux is recalculated after rounding.
Oxygen, Air, and Sludge
MBR systems need air for biology and membrane scouring. Carbon removal consumes oxygen. Nitrification adds a large oxygen demand. It also consumes alkalinity. Blowers must cover both process oxygen and scour air. Sludge wasting is also important. The selected SRT must be maintained. This tool estimates solids production and wasting flow. Final design should still include pilot data, manufacturer limits, local standards, and safety review.
FAQs
1. What does this calculator size?
It sizes major membrane bioreactor design items. These include reactor volume, HRT, membrane area, module count, oxygen demand, sludge wasting, alkalinity, and blower air flow.
2. What is membrane flux?
Membrane flux is the permeate flow through each square meter of membrane per hour. It is usually shown as LMH. Lower flux often improves fouling control.
3. Why is SRT important?
SRT controls biomass age. It affects nitrification, sludge yield, oxygen demand, and process stability. MBR systems often use higher SRT than conventional activated sludge systems.
4. Why is MLVSS used in F/M?
MLVSS estimates the active biological fraction of mixed liquor solids. Using MLVSS gives a better food to microorganism ratio than total suspended solids alone.
5. How is membrane module count calculated?
The calculator finds required membrane area from flow, flux, and operating hours. It adds redundancy. Then it divides by module area and rounds upward.
6. Does this replace detailed engineering design?
No. It supports preliminary design and option review. Final design should include membrane supplier data, local rules, wastewater testing, pilot results, and professional checking.
7. Why is alkalinity shown?
Nitrification consumes alkalinity. Low alkalinity can reduce pH and harm biological activity. The calculator estimates alkalinity demand as calcium carbonate equivalent.
8. What does TMP status mean?
TMP status compares estimated transmembrane pressure with the entered alarm limit. High TMP may indicate fouling risk, low permeability, or excessive operating flux.