What an MABR Process Flow Diagram Actually Shows
An MABR process flow diagram is a stream-numbered schematic of a Membrane Aerated Biofilm Reactor treatment train. It shows influent entering pretreatment, flowing through a gas-permeable hollow-fiber membrane module where oxygen is bubblelessly supplied through the membrane lumen to a counter-diffusion biofilm, then to post-treatment and effluent polishing. In pilot data, this train achieved over 90% NH₄⁺-N removal and 0.52 g-N/(m²·day) denitrification at 0.01 MPa intra-membrane pressure and 16 h HRT (per Biotechnology & Biotechnological Equipment pilot study, doi:10.1080/13102818.2017.1399826).
The MABR PFD differs structurally from a conventional activated-sludge PFD because oxygen is delivered through the membrane wall rather than bubbled into the bulk liquid. Substrate diffuses inward from the bulk liquid toward the biofilm, while oxygen diffuses outward from the membrane lumen — this counter-diffusion geometry is what allows a single biofilm to host both nitrifying bacteria (inner, oxygen-rich face) and heterotrophic denitrifiers (outer, substrate-rich face) (per wastewaterengineering.com MABR technical brief, 2025). On a PFD, the consequence is visible: a single membrane module replaces the aeration tank and recycle loop of a conventional nitrification–denitrification train.
Seven streams typically appear on an MABR PFD: (1) raw wastewater in, (2) screened influent, (3) equalized feed, (4) MABR effluent, (5) clarified or polished effluent, (6) waste activated sludge, and (7) aeration air supply. The convention used throughout this article is that each unit operation is a numbered block, and each stream is annotated with flow rate (m³/d) and the key constituent being tracked (NH₄⁺-N, COD, or DO). A draftsperson can reproduce the full train from the seven-block sequence: screening → equalization → MABR module → post-treatment → disinfection → sludge handling → effluent polishing.
The 2026 MABR Process Flow Diagram, Block by Block
The PFD is read from left to right, with air supply entering the MABR block from below and sludge withdrawal exiting to the dewatering block. Each block below names the equipment, the function, and the streams in and out.
Block 1 — Influent screening. A rotary mechanical bar screen for MABR headworks with 5–10 mm aperture removes rags, plastics, and fibrous material that would foul the downstream hollow fibers. Stream 1 (raw wastewater) enters; Stream 2 (screened solids) discharges to a dumpster, and the screened liquid passes to Block 2.
Block 2 — Equalization basin. Flow and load dampening with a typical hydraulic retention time of 6–12 h. Mixers keep solids in suspension; level control feeds the MABR at a stable C/N ratio of 8 (per the 2017 pilot study, doi:10.1080/13102818.2017.1399826). Stream 2 enters; Stream 3 (equalized feed) leaves at controlled flow.
Block 3 — MABR membrane module. The heart of the PFD. Gas-permeable hollow-fiber or flat-sheet membranes are bundled into cassettes; air is supplied to the lumen at 0.01–0.015 MPa, well below the bubble point. Stream 3 enters the shell side; Stream 7 (blower air) enters the lumen; Stream 4 (MABR effluent, NH₄⁺-N <14.5 mg/L, TOC <2 mg/L) exits to Block 4.
Block 4 — Post-treatment. A DAF unit downstream of the MABR module or a lamella clarifier captures detached biofilm solids. Effluent TSS before disinfection is typically below 30 mg/L. Stream 4 enters; Stream 5 (clarified effluent) leaves to Block 5; a side stream of waste solids routes to Block 6.
Block 5 — Disinfection. A chlorine dioxide generator for the disinfection block sized to peak flow provides a final barrier against fecal coliform before discharge or reuse. Stream 5 enters; polished effluent leaves the PFD boundary.
Block 6 — Sludge handling. Waste biofilm solids from Block 4 are thickened and dewatered on a plate-and-frame filter press for waste biofilm sludge. Filter cake exits to disposal; supernatant returns to Block 2, closing the water loop.
Block 7 — Effluent polishing or reuse storage. Optional MBR polishing or a reuse buffer tank for process-water recycle. This block is where the MABR train can be coupled to a downstream membrane cassette for reuse-grade effluent.
Operating Parameters Inside the MABR Block
The MABR block on the datasheet must carry a defined operating window, not just a flow arrow. The table below consolidates the pilot-verified envelope from the 2017 Biotechnology & Biotechnological Equipment study (doi:10.1080/13102818.2017.1399826) and aligns it with procurement-ready spec ranges for 2026.
| Parameter | Operating Range | Design Center Point | Source |
|---|---|---|---|
| Intra-membrane air pressure | 0.010–0.015 MPa | 0.012 MPa | Pilot, 2017 |
| Intra-membrane air flow rate | 0.005–0.020 cm/min | 0.010 cm/min | Pilot, 2017 |
| Hydraulic retention time (HRT) | 12–48 h | 16 h | Pilot, 2017 |
| Bulk dissolved oxygen (DO) | 0–6 mg/L | 2 mg/L (nitrification mode) | Pilot, 2017 |
| Hydraulic loading | 0.012–0.047 m³/(m²·day) | 0.025 m³/(m²·day) | Pilot, 2017 |
| Influent C/N ratio | 5–10 | 8 | Pilot, 2017 |
| NH₄⁺-N removal | 71–95% | 90% | Pilot, 2017 |
| Denitrification rate | 0.30–0.52 g-N/(m²·day) | 0.45 g-N/(m²·day) | Pilot, 2017 |
Two control regimes translate directly from this table. High-DO mode (bulk DO 1.5–6 mg/L at 0.015 MPa) favors nitrification and is the default start-up condition. Low-DO mode (bulk DO 0–0.5 mg/L at 0.010 MPa and 0.005 cm/min air flow) favors denitrification and reaches the peak rate of 0.52 g-N/(m²·day) reported in the pilot data. Operators typically swing between these two regimes by adjusting the blower rather than adding external carbon.
The hydraulic loading ceiling is the most consequential hard limit on the table: values above 0.047 m³/(m²·day) caused visible biofilm sloughing and pushed effluent TOC into the 20–30 mg/L range during the 2017 pilot (per doi:10.1080/13102818.2017.1399826). Real designs should derate the pilot ceiling to 0.020–0.030 m³/(m²·day) to keep biofilm attachment stable under variable industrial loads. The simultaneous nitrification–denitrification (SND) mechanism itself is well established: ammonia-oxidizing bacteria colonize the inner oxygen-rich face of the biofilm, and heterotrophic denitrifiers colonize the outer substrate-rich face, so no external carbon source is needed (per wastewaterengineering.com, 2025).
Worked Mass Balance Around the MABR Block
The mass balance below uses the 2017 pilot influent as the basis so a process engineer can replicate the numbers in a spreadsheet and cross-check blower and membrane sizing.
Basis: 1,000 m³/d industrial influent at NH₄⁺-N = 50 mg/L and COD = 200 mg/L, C/N = 8, HRT = 16 h. Daily NH₄⁺-N load = 1,000 m³/d × 50 g/m³ = 50 kg-N/d. Daily COD load = 200 kg/d.
Membrane area at the pilot ceiling. At the 0.047 m³/(m²·day) hydraulic-loading ceiling reported in the 2017 pilot, required membrane area = 1,000 / 0.047 ≈ 21,280 m². This is the theoretical minimum; production designs derate to 0.020–0.030 m³/(m²·day), which moves the required area to 33,000–50,000 m² for biofilm stability. The 21,280 m² figure should be used as a lower bound for feasibility only, not for procurement.
Predicted effluent quality. Applying the 2017 pilot removal envelope: NH₄⁺-N effluent <14.5 mg/L, equivalent to 71% removal at the worst pilot point and over 90% at the design center; TOC effluent <2 mg/L, equivalent to over 99% carbon removal on a TOC basis (per doi:10.1080/13102818.2017.1399826). For a 1,000 m³/d plant, this means roughly 35.5 kg-N/d discharged and less than 2 kg-TOC/d.
Air demand. At 0.01 cm/min intra-membrane air flow on 21,280 m² of hollow-fiber area, the volumetric air supply equals 21,280 m² × (0.01 cm/min × 0.0001 m/cm × 60 min/h) = 305 m³/h at standard conditions. The blower should be specified at 0.015 MPa discharge with a 20% margin, so the procurement rating is approximately 365 m³/h at 0.015 MPa. The same blower at 0.010 MPa covers the low-DO denitrification regime.
How the MABR PFD Differs from an MBR or Conventional Activated-Sludge PFD
A buyer who already operates a conventional activated-sludge or MBR plant needs a one-look comparison to judge whether the MABR configuration justifies a re-spec. The table below maps the three PFDs block by block.
| Block | Conventional AS PFD | MBR PFD | MABR PFD |
|---|---|---|---|
| Oxygen delivery | Diffused-air bubble aeration in mixed liquor | Coarse-bubble aeration under membrane cassette | Bubbleless lumen-to-biofilm diffusion at 0.010–0.015 MPa |
| Biomass phase | Suspended flocs | Suspended flocs + membrane-retained solids | Attached counter-diffusion biofilm on hollow fibers |
| Solid–liquid separation | Secondary clarifier | Submerged UF/MF membrane cassette | DAF or lamella clarifier (smaller than MBR cassette) |
| Stages for nitrogen removal | Multiple (aerobic + anoxic zones with recycle) | Multiple (aerobic + anoxic zones with recycle) | Single stage (SND inside one biofilm) |
| NH₄⁺-N removal (pilot) | 80–95% across multi-stage train | over 90% at short HRT | over 90% in a single stage |
| External carbon for denitrification | Typically required | Typically required | Not required (per 2017 pilot, doi:10.1080/13102818.2017.1399826) |
The structural difference is what changes the PFD most. In an MBR, the membrane's job is solid–liquid separation; the PFD's post-block is large. In an MABR, the membrane's job is oxygen delivery, so the post-block can be a compact DAF or a lamella clarifier for the MABR post-block. For plants that need reuse-grade effluent, an MBR polishing block downstream of MABR is a common 2026 configuration. MABR also collapses two process stages into one — the 2017 pilot achieved over 60% nitrogen removal in a single stage where ecological alternatives such as EFB and constructed wetlands need multiple stages with HRTs of 36 h to several days (per doi:10.1080/13102818.2017.1399826). On energy, the bubbleless lumen aeration and counter-diffusion geometry give high oxygen transfer efficiency; both the 2017 pilot and the wastewaterengineering.com brief describe the energy advantage qualitatively without publishing a kWh figure, so any specific kWh/m³ number should be sourced from the equipment vendor rather than invented here.
Procurement Checklist: Equipment to Specify on the MABR PFD
The PFD only becomes useful when each block is mapped to a quotable equipment line. The list below names the equipment that should appear on the procurement schedule, in the same order as the PFD blocks above.
- Headworks: rotary mechanical bar screen, 5–10 mm aperture, sized to peak daily flow.
- Equalization: equalization basin with mechanical mixers and level-control instrumentation; HRT 6–12 h.
- MABR module: gas-permeable hollow-fiber membrane cassette, factory-tested for bubble point and pressure rating; air-supply header with non-return valve.
- Post-treatment: DAF or lamella clarifier for detached-biofilm solids capture, sized to peak solids flux.
- Disinfection: chlorine dioxide generator sized to peak flow with two chemical-feed skids for redundancy.
- Sludge dewatering: plate-and-frame filter press with cake handling and polymer preparation.
- Controls: PLC with DO probes, intra-membrane pressure transmitters, and airflow meters; optional remote monitoring via the automatic chemical dosing system telemetry link.
- Blower: positive-displacement or multistage centrifugal blower rated for 0.015 MPa discharge at the calculated air demand plus 20% margin (roughly 365 m³/h for the 1,000 m³/d basis above).
For a deeper treatment of the biofilm mechanism, the MABR counter-diffusion biofilm mechanism explainer walks through the diffusion geometry. For energy benchmarking against other biofilm reactors, the aeration energy benchmark for biofilm reactors provides a 2026 kWh reference. For OPEX on the post-treatment block, the DAF OPEX data for the post-treatment block is a useful cross-check.
Frequently Asked Questions
What does a typical MABR process flow diagram include?
A typical MABR PFD includes seven blocks — influent screening, equalization, the MABR membrane module, post-treatment (DAF or lamella), disinfection, sludge dewatering, and effluent polishing — connected by seven streams covering raw wastewater, screened influent, equalized feed, MABR effluent, clarified effluent, waste sludge, and aeration air supply (per the 2017 pilot, doi:10.1080/13102818.2017.1399826).
What influent and effluent parameters define the MABR design envelope?
The 2017 pilot used 50 mg/L NH₄⁺-N and 200 mg/L COD at a C/N ratio of 8, and produced effluent with NH₄⁺-N below 14.5 mg/L and TOC below 2 mg/L. At the design center this corresponds to over 90% NH₄⁺-N removal and over 99% TOC removal (per doi:10.1080/13102818.2017.1399826).
What operating pressure and air flow should be specified on the PFD?
Specify intra-membrane air pressure of 0.010–0.015 MPa and an air flow rate of 0.005–0.020 cm/min. The 2017 pilot reported peak denitrification of 0.52 g-N/(m²·day) at 0.005 cm/min and 0.01 MPa; the blower should be sized for 0.015 MPa with a 20% margin.
What HRT and hydraulic loading limits apply to an MABR?
HRT should be specified in the 12–48 h range, with 16 h as the design center. Hydraulic loading must stay below 0.047 m³/(m²·day); above that ceiling, biofilm sloughing drives effluent TOC into the 20–30 mg/L range (per doi:10.1080/13102818.2017.1399826).
How does an MABR PFD differ from an MBR PFD?
In an MBR, the membrane's job is solid–liquid separation, so the post-block is a submerged UF/MF cassette. In an MABR, the membrane's job is oxygen delivery, and the post-block is a smaller DAF or lamella clarifier — which is why the MABR PFD shows a compact post-block and a single biofilm stage instead of an MBR's aerobic-plus-anoxic recycle train.
