MBR 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.
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. 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. 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.
Backwash / Backflush BW
A membrane cleaning technique where treated permeate is pumped in reverse direction through the membrane to dislodge accumulated foulants. Typically performed for 30-60 seconds every 15-30 minutes during filtration.
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). A key indicator of wastewater strength and treatment efficiency.
Context: MBRs effectively remove BOD, typically achieving effluent BOD concentrations below 5 mg/L.
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 maintain high biomass concentrations (8,000-12,000 mg/L MLSS), enabling efficient treatment in compact systems.
Chemical Oxygen Demand COD
The amount of oxygen required to chemically oxidize all organic and inorganic matter in wastewater. A broader measure of water pollution than BOD, as it includes non-biodegradable compounds.
Context: MBRs achieve significant COD removal, typically 85-95%, making them suitable for stringent discharge limits.
Clean-in-Place CIP
An intensive membrane cleaning procedure using higher concentrations of chemicals (sodium hypochlorite, citric acid, caustic) to remove irreversible fouling. Typically performed monthly to quarterly, involving soaking membranes for several hours.
Context: CIP is essential for maintaining long-term membrane performance and preventing permanent flux decline in MBRs.
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: MBRs excel at denitrification due to their ability to create distinct anoxic zones and maintain slow-growing denitrifying bacteria.
Dissolved Oxygen DO
The concentration of oxygen dissolved in water, typically measured in mg/L. Essential for aerobic biological treatment. Optimal levels in MBRs are typically 1-3 mg/L.
Context: DO control is critical in MBRs to balance aerobic treatment efficiency with energy consumption for aeration.
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: Typical MBR flux ranges from 15-30 LMH. Higher flux increases fouling risk; lower flux reduces energy efficiency.
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 the primary operational challenge in MBRs. Effective pre-treatment and routine cleaning are essential to manage it.
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 increasingly used for municipal and industrial wastewater treatment due to their compact footprint and superior effluent quality.
Microfiltration MF
A membrane filtration process with pore sizes typically between 0.1-10 µm. Removes suspended solids, bacteria, and some viruses but not dissolved solids or small molecules.
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: MBRs typically operate at MLSS concentrations of 8,000-12,000 mg/L, significantly higher than conventional activated sludge (3,000-5,000 mg/L).
Nitrification N Oxidation
An aerobic biological process where ammonia (NH₄⁺) is oxidized to nitrite (NO₂⁻) and then to nitrate (NO₃⁻) by autotrophic bacteria (Nitrosomonas and Nitobacter). Essential for nitrogen removal from wastewater.
Context: MBRs are highly effective at nitrification due to their long sludge retention times, which allow slow-growing nitrifying bacteria to thrive.
Permeate Treated Water
The filtered water that passes through the membrane and exits the MBR system as treated effluent. High-quality water suitable for discharge or reuse.
Context: MBR permeate typically has very low turbidity (<0.1 NTU), suspended solids (<1 mg/L), and BOD (<5 mg/L).
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. Typically includes screening and grit removal.
Context: Adequate pre-treatment is critical for MBR success, protecting membranes and reducing fouling and operational costs.
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: MBRs typically operate at SRTs of 10-30 days, much longer than conventional activated sludge, enabling nitrification and advanced treatment.
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: MBRs achieve excellent suspended solids removal, typically producing effluent with TSS <1 mg/L.
Transmembrane Pressure TMP
The pressure difference across the membrane, calculated as the average of inlet and outlet pressures minus the permeate pressure. A key indicator of membrane fouling and system performance.
Context: Increasing TMP over time indicates fouling. Routine monitoring and cleaning are performed when TMP exceeds design limits (typically 0.3-0.5 bar).
Ultrafiltration UF
A membrane filtration process with pore sizes typically between 0.01-0.1 µm. Removes suspended solids, bacteria, viruses, and some macromolecules but not dissolved solids.
Context: UF membranes in MBRs provide superior effluent quality compared to microfiltration but operate at higher pressures and may experience greater fouling.