Glossary of Terms

Glossary of Terms

Glossary of Terms

AAF
Average Annual Flow. The net daily flow requirement of a treatment system averaged annually.
Activated Sludge
Activated sludge is a biological flow produced by aerating sewage and separating solids using a clarifier or membrane. This form of biological treatment reduces biologically degradable contaminants.
Aerobic
Condition that indicates the presence of oxygen, usually in an activated sludge process. Aerobic conditions in activated sludge reduce BOD and convert ammonia to nitrates.
Alkalinity
Alkalinity is a measure of the capacity of water to neutralize acids and is also known as the buffering capacity. It is due to the presence of calcium and magnesium salts. Alkalinity is consumed in the nitrification process and produced in the denitrification process and is a necessary constituent of activated sludge.
Alpha
Correction factor used in aeration calculations. It accounts for the difference in oxygen transfer efficiency between clean water and sewage. The presence of solids and dissolved materials in wastewater reduces oxygen transfer efficiency.
Ammonia-N
The concentration of ammonia in wastewater reported in mg of Nitrogen per liter of water (mg/L)
Ammonification
Process by which organic nitrogen is converted to ammonia in activated sludge processes.
Anaerobic
Absence of oxygen, nitrates, or sulfates in an activated sludge process. This condition is necessary for enhanced biological phosphorus removal.

Anaerobic also describes a process of wastewater treatment where anaerobic conditions promote the growth of anaerobic bacteria to reduce BOD or COD. This method of treatment is typically used in high strength wastes.
Anoxic
Condition created from an absence of oxygen in an activated sludge system, where nitrates or sulfates are present. This condition is necessary for denitrification.
Autotrophic Bacteria
In activated sludge, Autotrophic Bacteria are strictly aerobic bacteria that obtain their carbon for cell growth from carbon dioxide or calcium carbonate and their energy from the oxidation of ammonia. They are responsible for the nitrification process and typically account for about 10% of the biomass in activated sludge.
Backwash
Backwash or backpulse is a membrane process where the flow of water through the membrane is temporarily reversed to dislodge solids that have accumulated on the membrane surface.
Bio-P
Bio-P or EBPR (enhanced biological phosphorus removal) is an activated sludge process used to remove phosphorus biologically.
BOD
Biochemical Oxygen Demand. The amount of oxygen required to biologically metabolize the biodegradable portion of a sample of wastewater. It is a measure of the wastewater strength.
Cake Layer
A layer of solids and colloidal material on the surface of the membrane. Managing the thickness of the cake layer by mechanical action against the membrane surface or backwash maintains membrane performance.
CBOD
Carbonaceous Biochemical Oxygen Demand. Similar to BOD, except the oxygen required to metabolize any nitrogen in the sample is omitted by use of an inhibitor that prevents nitrification.
CIP
Clean In Place. A method of cleaning a membrane system without removing any parts. Typically, a CIP is performed by removing process fluid and pumping a cleaning solution into the membrane skid.
COD
Chemical Oxygen Demand. The amount of oxygen required to chemically oxidise a sample of wastewater. Measured in mg/L. COD is a measure of the strength of waste.
Concentrate Return
In membrane systems, concentrate return is the concentrated portion of the feed, and is returned to the process basin or feed tank.
Critical Flux
The maximum flux rate sustainable by a membrane system. Operation above critical flux results in an exponential increase in TMP.
DBOOM
Design, Build, Own, Operate, Maintain. A procurement method by which Dynatec installs, owns, and operates the treatment equipment without capital costs to the customer. Customers pay per gallon of wastewater treated on a contract basis.
Denitrification
In activated sludge, the process of converting nitrates to nitrogen gas. Heterotrophic bacteria use nitrate as an oxygen source in anoxic conditions to consume organic compounds.
DO
Dissolved Oxygen. A measure of the concentration of oxygen in water. Measured in mg/L.
EBPR
Enhanced Biological Phosphorus Removal. An activated sludge process used to remove phosphorus biologically.
EPS
Extracellular Polymeric Substance. In activated sludge, these substances are secreted by microorganisms and thought to foul membranes.
Ferric Chloride
Trivalent chlorinated iron. An inorganic coagulant used to remove phosphorus or other chemically precipitated dissolved compounds.
Flux
The permeate rate per unit area of membrane surface. Units are gfd (gallons of permeate per square foot of membrane are per day) or LMH Liters of permeate per square meter of membrane are per hour.
FOG
Fats, Oils, and Grease. Organic polar compounds derived from animal, plant, or vegetable compounds that are composed of long chain triglycerides.
Fouling
A normal process by which a membrane filter becomes clogged. Periodic chemical cleaning is necessary to remove the foulants and return the membrane to service.
GFD
Gallons per square foot per day, a measure of membrane flux.
GPH
Gallons Per Hour
GPM
Gallons Per Minute
Grit
The heavy material present in wastewater such as sand.
Gross Flux
The instantaneous flux rate at any given moment.
Headloss
The pressure lost by a fluid flowing through a conduit or pipe caused by friction.
Headworks
In a wastewater treatment process, headworks is the equipment designed to remove and handle large solids and screenings. Equipment includes raw water screening and conveying of solids.
Heterotroph
A type of bacteria that uses organic matter for energy and growth, and can use free oxygen, nitrates, or sulfates for an oxygen source. In activated sludge, heterotrophs are responsible for BOD reduction and denitrification.
HMI
Human Machine Interface. A panel mounted screen the operator obtains information from and controls the system.
HRT
Hydraulic Retention Time. Typically, the system volume divided by the influent flow rate.
I/O
Input / Output. A part of the PLC that accepts electrical inputs from instruments and sends electrical outputs to actuate automated devices such as valves or motors.
Influent
Untreated wastewater entering a treatment system.
LEED
Leadership in Energy and Environmental Design. LEED is an internationally recognized green building certification system for buildings designed to meet energy savings, water efficiency, and emissions reduction.

LEED buildings often integrate wastewater treatment systems in the building to provide reuse water.
MBBR
Moving Bed Biofilm Reactor. An activated sludge process that uses a moving bed of media which forms a substrate for attached growth in the bioreactor.
MBR (Membrane bioreactor)
Membrane biological reactor. An activated sludge process where membranes are used for solid/liquid separation.
MCC
Motor Control Center. Enclosed area housing the starters, VFD's, and overload protection equipment used in a system to run motors.
Membrane
A layer material which serves as a selective barrier between two phases and remains impermeable to specific particles, molecules, or substances when exposed to the action of a driving force.
Membrane Life
The period of time a membrane is last before needing replaced.
Membrane Module
An assembled unit containing individual membrane tubes.
MGD
Million Gallons per Day
Mixed Liquor
In activated sludge systems, a mixture of water, organic material, active and inactive biomass.
MLSS
Mixed Liquor Suspended Solids. The mass concentration of the solid portion of Mixed Liquor. Units are in mg/L.
MLVSS
Mixed Liquor Volatile Suspended Solids. The portion of the MLSS that is vaporized when the MLSS is heated to 500C for 10 minutes. Units are as a percentage of MLSS. MLVSS is referred to as the active biomass.
MMF
Maximum Month Flow. The maximum flow expected in a given month averaged daily.
Nanofilter
Nanofilter is a type of membrane filter used to remove large dissolved molecules and some ions. Membrane rejection is measured in molecular weight of molecules rejected by the membrane.
Net Flux
The total amount of permeate produced available for discharge in a given time.
Nitrification
In activated sludge, the aerobic biological process carried out by autotrophic bacteria where ammonia is converted to nitrates. This process consumes alkalinity.
Nitrobacter
A species of autotrophic bacteria responsible for nitrification.
Nitrogen
In wastewater, nitrogen is a nutrient in the form of organic nitrogen, ammonia, nitrates, or nitrites that often must be removed from the wastewater through the use of nitrification and denitrification processes.
Nitrosonomas
A species of autotrophic bacteria responsible for nitrification.
NTU
Nephelometric Turbidity Unit. A measure of the clarity of water.
O&M
Operation and Maintenance
Organic Nitrogen
In wastewater, a compound containing nitrogen and organic carbon.
Oxic
In activated sludge, a condition describing the presence of oxygen.
P&ID
Piping and Instrumentation Diagram. A schematic diagram showing all equipment, piping, valves, instruments, and controls.
PAO
Phosphorus Accumulating Organism. These type of bacteria are responsible for biological phosphorus removal.
PDF
Peak Daily Flow. The maximum flow that a system is designed for over one day.
Permeability
Specific flux. A measure of driving force required to produce a given flow of permeate per unit area of membrane surface. Measured in GFD/PSI or LMH/Bar.

Permeability declines as a membrane becomes fouled.
PHF
The maximum flow a system is designed for over one hour.
PLC
Programmable Logic Controller. An industrial computer used to control the system.
Process Train
The smallest stand alone portion of the process. Systems have one or more process trains. Multiple process trains are used to provide redundancy or operational flexibility.
Q
Q is the variable often used for the design flow of a wastewater system.
RO Membrane
Reverse Osmosis membrane. RO membranes are used to separate dissolved materials from water and are rated in terms of NaCl rejection. All RO membranes are capable of at least 99% salt rejection.
SCADA
Supervisory Control and Data Acquisition. The SCADA system is a control function and is the software used to provide data logging and control to the operator.
SCFM
Standard Cubic Feet per Minute. A mass flow rate of air or other gases.
Seeding
Adding a small amount of bacteria to a biological system during startup.
Sludge Yield
In activated sludge or MBR systems, the amount of waste sludge generated per mass of BOD removed by the system.
SNdN
Simultaneous Nitrification and Denitrification. In activated sludge systems, nitrification and denitrification can be achieved in a single basin under certain conditions.
Soluble Unbiodegradable TKN
The portion of the nitrogen in wastewater that cannot be removed biologically, or with ultrafiltration membranes.
Spiral Wound Membrane
A configuration of membrane used for nanofiltration and reverse osmosis consisting of a rolled membrane sheet. Spiral wound membranes require solids free feed.
SRT
Solids Retention Time. The average time the activated-sludge solids are in the system. SRT gives a relative description of the sludge age of a system and is related to the systems operating point on the growth curve of the biomass.
SSR
Single Source of Responsibility. Procurement method by which a single company is used to provide the equipment, controls, and support for the major portion of a project. The advantage to SSR is minimizing coordination costs and errors during construction, while giving the operator a single point of contact for support.
Submerged Membrane
A membrane configuration where the membrane is cast onto the outside surface of a substrate. The membrane is submerged into the feed or dirty water and permeate passes through the membrane from the outside in. Submerged membranes are typically offered in flat plate or hollow fiber configurations for wastewater.
Subsystem
The treatment system is comprised of subsystems such as chemical cleaning, membrane, backwash, and others.
Surfactant
A chemical agent capable of reducing the surface tension of a liquid into which it is dissolved. Surfactants are used in soaps and detergents.
Sustainable Flux
The flux rate at which the membrane system can operate for extended periods of time. Sustainable flux is a flux rate below critical flux.
TDS
Total Dissolved Solids. The amount of residue of a sample of filtered water. The measure of dissolved materials in water.
Theta
In wastewater aeration systems, the temperature correction factor.
TIN
Total inorganic nitrogen. In wastewater, the NH3 + NO3 + NO2.
TKN
Total Kjehldahl Nitrogen. The amount of ammonia, ammonium and organic nitrogen in a sample, expressed in mg of N per L of water.
TMP
Transmembrane Pressure. The pressure differential across the membrane surface. The measure of the driving force required to produce permeate.
TN
Total Nitrogen. The sum of the TKN, nitrite, and nitrate of a sample expressed in mg of N per L of water.
Treatability
A term used to describe the effectiveness of a treatment process on a specific type of wastewater.
TS
Total Solids. The sum of the TSS and the TDS.
TSS
Total Suspended Solids. The mass of solids contained in a sample that can be filtered with a 0.45 micron filter and dried.
Tubular Membrane
A membrane configuration where the membrane is cast on the inside of a substrate tube. One or more tubes are configured into a module. Feed is pumped to the inside of the tube and permeate passes through the sidewall of the tube.
Turbidity
The measure of the cloudiness of water measured by the amount of light that can pass through a sample.
TVS
Total Volatiles Solids. The portion of the solids of a sample that can volatilize or burned at 500 C.
UV
Ultraviolet Light. Exposing water to ultraviolet light is one way of disinfecting the water.
VFD
Variable Frequency Drive. A device that is used to control the frequency of electricity feeding a motor. It can vary the speed of the motor from a signal produced from a PLC or other device.
Viscosity
The resistance of a liquid to shear or tensile stresses. A measure of the thickness of liquid.
VSS
Volatile Suspended Solids. The portion of the TSS that can be volatilized or burned at 500 C.
WAS
Waste Activated Sludge. In activated sludge systems, the excess biological solids which are removed from the system. Activated Sludge systems produce WAS and treated water.
Yield
In activated sludge systems, yield (Y) is the mass of biomass produced per unit mass of BOD removal.
ZLD
Zero Liquid Discharge. A wastewater treatment system that produces no liquid waste stream.