Membrane Bioreactor (MBR) Wastewater Design Simulator

Large-scale municipal sewage: Reference projects such as Paris Seine Aval (a 300,000 m³/day MBR stage), the Beijing Olympic reuse plant and the Singapore Changi NEWater factory show MBRs at city scale. They replace CAS + sand filtration + UV disinfection in a single step, shrinking the footprint to a third or half of a conventional plant. Inputting Q=50,000–100,000 m³/day in this tool quickly shows that 100,000 m² of membrane area is a realistic order of magnitude.

Food and beverage wastewater: Streams from Coca-Cola, Pepsi or breweries carry BOD of 500–2,000 mg/L plus suspended solids, fats and oils. An MBR delivers a complete solid–liquid split that lets the site reuse the permeate for cooling-towers or wash-down, hitting discharge limits and water cost at the same time. Flat-sheet Kubota K-3 modules are popular here for their easy cleaning.

Decentralised and small-scale treatment: Hotels, resorts, remote islands and container ships lack a sewer connection. MBRs are compact, start up quickly and automate easily. At Q=50–500 m³/day they are now often more efficient than a CAS plus MF train. Try the bottom end of the flow slider in this tool.

Water reuse: MBR permeate is essentially SS-free and bacteria-free, which makes it an ideal pre-treatment for downstream reverse osmosis (RO). A reuse train such as "activated sludge → MBR → RO → UV" is the de-facto standard for NEWater-style industrial and indirect potable reuse. If the MBR is not running stably, the downstream RO fouls aggressively, so the CIP management this tool helps you size really determines the stability of the whole reuse chain.

The biggest trap is the simple-minded view that "higher flux means less membrane and lower capex". Yes, A=Q/J halves when you double the flux, but the fouling rate goes roughly as J², so doubling the flux quadruples fouling. The CIP interval drops by a factor of four (monthly cleaning becomes twice a week), annual chemical cost roughly multiplies by five and membrane life shrinks. Add in extra scour air to keep the membrane surface shear up, and energy explodes too. On a Life-Cycle-Cost basis the optimum almost always sits at 18–22 LMH. Don't let a vendor talk you into an aggressively high design flux without checking the resulting CIP interval and membrane area together in a tool like this.

Second, the idea that "if MLSS goes up the reactor can shrink without limit". Volume does scale roughly as 1/MLSS in theory, but above 15,000 mg/L the sludge viscosity jumps, the oxygen-transfer α-factor drops below 0.5 and aeration power has to more than double. The fouling layer on the membrane also gets thicker, accelerating TMP rise. Real MBRs typically settle around 10,000–13,000 mg/L MLSS, where compaction and aeration efficiency balance out. Anything beyond that is research territory. If you key in MLSS=18,000 here the computed volume is small, but please remember that the real plant behaves very differently.

Finally, the over-confidence that "as long as the permeate looks clean, MBR solves everything". An MBR removes SS and bacteria perfectly, but soluble COD, nutrients (N and P) and trace pollutants (pharmaceuticals, PFAS) need their own removal mechanisms. Nitrogen removal requires nitrification + denitrification stages, phosphorus removal needs either chemical precipitation or biological-P configurations such as A2O. PFAS and recalcitrant organics need activated carbon or RO behind the MBR. The MBR is the gold standard for physical separation, not a substitute for biological or chemical treatment.