Membrane Bioreactor Glossary of Terms
This glossary provides definitions and explanations of technical terms, acronyms, and concepts commonly used in Membrane Bioreactor (MBR) technology and wastewater treatment. Use the search box below to quickly find terms, or scroll through the complete list.
Showing all glossary terms.
A
Activated Sludge
A biological wastewater treatment process in which microorganisms (bacteria, protozoa, fungi) are suspended in a mixed liquor and aerated to degrade organic matter. [G-S2] The biomass is then separated from the treated water, with a portion recycled back to the bioreactor to maintain the microbial population.
Context: MBRs are an advanced form of activated sludge treatment, replacing gravity settling with membrane filtration for solids separation.
Aeration Air Supply
The process of introducing air into the bioreactor to provide dissolved oxygen (DO) for aerobic biological treatment. [G-S1][G-S2] Aeration can be supplied via diffusers (coarse or fine bubble) or mechanical aerators.
Context: In MBRs, aeration serves dual purposes: providing oxygen for biological treatment and providing air scouring to reduce membrane fouling.
B
Backwash / Backflush BW
A membrane cleaning technique where treated permeate is pumped in reverse direction through the membrane to dislodge accumulated foulants. [G-S1] Cycle duration and frequency are configuration- and OEM-specific; do not treat a generic interval as a universal MBR setting.
Context: Backwashing is a routine maintenance procedure in MBRs to manage reversible fouling and extend membrane life.
Biological Oxygen Demand BOD
The amount of oxygen required by microorganisms to decompose organic matter in wastewater. Typically measured over 5 days at 20°C (BOD₅). [G-S4] A key indicator of wastewater strength and treatment efficiency.
Context: Selected EPA-cited facility/vendor cases reported average effluent BOD of 1–2 mg/L; actual performance depends on wastewater, process configuration, permit, sampling basis, and operating period.
Biomass Microorganisms
The living microorganisms (bacteria, protozoa, fungi) suspended in the bioreactor that perform the biological treatment of wastewater. Often quantified as Mixed Liquor Suspended Solids (MLSS).
Context: MBRs can operate at higher MLSS than many conventional activated-sludge designs, but the applicable range is site-, membrane-, oxygen-transfer-, viscosity-, solids-age-, and OEM-dependent; no universal range is stated here.
C
Chemical Oxygen Demand COD
An analytical measure of oxygen demand under a specified chemical-oxidation method. [G-S5] COD is often used alongside BOD to characterize wastewater strength; method scope and wastewater chemistry determine interpretation.
Context: COD removal is wastewater- and process-specific. Use a documented facility, pilot, permit, or manufacturer dataset with its sampling period and basis rather than a universal percentage.
Clean-in-Place CIP
An intensive membrane cleaning procedure using chemicals selected for the membrane material, foulant, OEM limits, safety controls, and waste-handling requirements. Chemistry, concentration, interval, and soak duration are not universal MBR values.
Context: CIP is essential for maintaining long-term membrane performance and preventing permanent flux decline in MBRs.
D
Denitrification N Removal
An anoxic biological process where nitrate (NO₃⁻) is reduced to nitrogen gas (N₂) by heterotrophic bacteria. Requires an anoxic environment (low dissolved oxygen) and readily available organic carbon.
Context: MBR systems can incorporate anoxic zones and internal recycle for denitrification when designed and operated for the required carbon, mixing, DO, temperature, and loading conditions.
Dissolved Oxygen DO
The concentration of oxygen dissolved in water, typically measured in mg/L. It is essential for aerobic biological treatment; an applicable target depends on reactor zone, nitrification objective, oxygen-transfer capacity, membrane configuration, and control strategy.
Context: DO control is critical in MBRs to balance aerobic treatment efficiency with energy consumption for aeration.
F
Flux Permeate Flow Rate
The volume of permeate (treated water) produced per unit membrane area per unit time, typically expressed in L/m²/h (LMH). A key operational parameter in MBRs.
Context: Flux is reported in L/m²·h (LMH). The usable range depends on membrane product, wastewater, temperature, MLSS, operating mode, cleaning state, and OEM design basis; no universal MBR range is stated here.
Fouling Membrane Clogging
The accumulation of foulants (organic matter, inorganic salts, microorganisms) on or within the membrane pores, reducing permeate flux and increasing transmembrane pressure. Can be reversible (removable by physical cleaning) or irreversible (permanent).
Context: Fouling is a major MBR operating consideration. Pretreatment, biological control, air scouring, monitoring, and OEM-approved cleaning should be selected according to the actual foulant and process conditions.
M
Membrane Bioreactor MBR
A wastewater treatment process combining biological treatment (activated sludge) with membrane filtration (microfiltration or ultrafiltration) to separate treated water from biomass. Produces high-quality effluent suitable for reuse or stringent discharge limits.
Context: MBRs are used in municipal and industrial wastewater treatment and can support reuse or stringent limits when the complete treatment train meets applicable permit and reuse requirements.
Microfiltration MF
A membrane filtration process generally described around the microfiltration range, with pore-size convention and rating method stated by the source or product. [G-S3] MF can remove suspended solids and many microorganisms, but dissolved-solute removal is not implied.
Context: MF membranes are commonly used in MBRs for their lower fouling tendency and lower operating pressure compared to ultrafiltration.
Mixed Liquor Suspended Solids MLSS
The concentration of suspended solids (primarily biomass) in the bioreactor, measured in mg/L. A key operational parameter indicating biomass concentration and treatment capacity.
Context: MBR and conventional activated-sludge MLSS ranges vary with process objective, membrane/OEM limits, oxygen transfer, viscosity, solids age, and wastewater. Compare named design bases rather than universal ranges.
N
Nitrification N Oxidation
An aerobic biological process where ammonia (NH₄⁺) is oxidized to nitrite (NO₂⁻) and then to nitrate (NO₃⁻) by autotrophic nitrifying microorganisms [G-S1], including genera such as Nitrosomonas and Nitrobacter. The organisms and conditions present depend on the system and operating history.
Context: MBRs are highly effective at nitrification due to their long sludge retention times, which allow slow-growing nitrifying bacteria to thrive.
P
Permeate Treated Water
The filtered water that passes through the membrane and exits the MBR system as treated effluent. [G-S1] High-quality water suitable for discharge or reuse.
Context: Permeate quality must be stated for a named facility, process train, permit, sampling period, and analytical basis. Do not treat turbidity, TSS, or BOD thresholds as universal MBR guarantees.
Pre-treatment Influent Preparation
Processes applied to wastewater before the bioreactor to remove large solids, grit, and other materials that could damage membranes or foul the system. May include screening, grit removal, and other protection selected for the influent and membrane supplier’s requirements.
Context: Adequate pre-treatment is critical for MBR success, protecting membranes and reducing fouling and operational costs.
S
Sludge Retention Time SRT
The average time that biomass is retained in the bioreactor, calculated as the ratio of biomass inventory to daily sludge wasting. A key design parameter affecting treatment performance and sludge production.
Context: SRT is selected for the biological objectives, temperature, loading, membrane/OEM constraints, wasting strategy, and permit. Longer SRT can support nitrification, but no universal MBR range is stated here.
Suspended Solids SS / TSS
Particles suspended in water that do not dissolve. Measured in mg/L. Total Suspended Solids (TSS) includes all suspended particles; Volatile Suspended Solids (VSS) refers to organic solids.
Context: Membrane separation can produce low suspended-solids concentrations, but reported TSS depends on integrity, sampling method, operating period, and the complete treatment train; use named data rather than a universal threshold.
T
Transmembrane Pressure TMP
The pressure difference across the membrane, calculated as the average of inlet and outlet pressures minus the permeate pressure. [G-S3] A key indicator of membrane fouling and system performance.
Context: Increasing TMP can indicate increasing hydraulic resistance or fouling. Monitoring and cleaning triggers must follow the selected membrane/OEM operating envelope and site trend basis; no universal 0.3–0.5 bar trigger is stated here.
Ultrafiltration UF
A membrane filtration process generally described around the ultrafiltration range, with pore-size convention and rating method stated by the source or product. [G-S3] UF can retain particles and some macromolecules; dissolved-solute removal depends on the solute and membrane.
Context: MF and UF selection depends on validated removal, pore-rating convention, TMP/flux, fouling behavior, cleaning, material, and lifecycle basis; neither is universally superior for every MBR application.
Use the terms in context: Continue from definitions to the Membrane Types & Materials guide or the Biological Process Calculators when applying terminology to a project basis.
Auditable source register for definitions and ranges:
- [G-S1] Government fact sheet, 2007: U.S. EPA, Membrane Bioreactors — Wastewater Management Fact Sheet, stable PDF. Supports general MBR process, air-scour/back-pulse context, permeate definition, and named facility/vendor results—not universal operating ranges.
- [G-S2] Government fact sheet, 2000: U.S. EPA, Package Plants, stable PDF. Supports activated-sludge and aeration definitions; conventional examples are not MBR setpoints.
- [G-S3] Government membrane manual, 2005: U.S. EPA, Membrane Filtration Guidance Manual, stable record. Supports MF/UF terminology, pore-size qualifications, and fouling terminology; it is not an MBR operating standard.
- [G-S4] USGS technical method, 2003: Five-Day Biochemical Oxygen Demand, stable PDF. BOD₅ basis: five-day incubation at 20 °C under the stated method.
- [G-S5] EPA analytical methods, 1993/1997: COD Method 410.4 and TSS Method 160.2, COD record and TSS record. These define analytical method scope and calculation basis, not MBR performance guarantees.
Editorial basis: A definition may be source-supported while an operating range remains site-, product-, or permit-dependent. Ranges removed from this page are not silently replaced with invented defaults.