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Glossary
Wastewater treatment terminology
A
Activated Sludge: Biological treatment process using suspended microbial growth with aeration and return sludge.
ADM1: Anaerobic Digestion Model No. 1, IWA standard model for anaerobic processes.
Aeration: Process of adding oxygen to water, typically using diffusers or mechanical aerators.
Alkalinity: Measure of water's buffering capacity, important for nitrification.
Ammonia (NH3/NH4): Reduced form of nitrogen; NH4+ is ammonium ion, NH3 is free ammonia.
Anoxic: Condition with no dissolved oxygen but nitrate present as electron acceptor.
ASM1/2d/3: Activated Sludge Models developed by IWA for process simulation.
B
BNR: Biological Nutrient Removal - removal of nitrogen and phosphorus using biological processes.
BOD: Biochemical Oxygen Demand - oxygen consumed by microorganisms to decompose organic matter.
Biogas: Mixture of CH4 and CO2 produced by anaerobic digestion.
Biofilm: Layer of microorganisms attached to a surface.
Biomass: Living microbial mass in biological treatment systems.
C
COD: Chemical Oxygen Demand - total oxygen required to chemically oxidize organic matter.
CSTR: Continuously Stirred Tank Reactor - completely mixed reactor vessel.
Clarifier: Tank for gravity separation of solids from liquid.
Colloidal: Particles between 0.001 and 1 micrometer, neither truly dissolved nor settleable.
D
Denitrification: Biological conversion of nitrate to nitrogen gas under anoxic conditions.
Detention Time: Average time water or sludge remains in a unit (HRT or SRT).
DO: Dissolved Oxygen - concentration of oxygen dissolved in water.
DWF: Dry Weather Flow - average flow during dry weather periods.
E
EBPR: Enhanced Biological Phosphorus Removal - P removal using PAOs.
Effluent: Treated water discharged from treatment process.
Endogenous: Related to cell decay and internal respiration.
EQ: Equalization - flow/load balancing basin.
F
F/M: Food to Microorganism ratio - organic loading rate relative to biomass.
Floc: Aggregation of particles and microorganisms in activated sludge.
Flocculation: Process of particle aggregation.
G
GAO: Glycogen Accumulating Organisms - compete with PAOs without P storage.
GHG: Greenhouse Gas - gases that trap heat in atmosphere (CO2, CH4, N2O).
Grit: Heavy inorganic particles (sand, gravel) removed in preliminary treatment.
H
HRT: Hydraulic Retention Time - average liquid residence time in a vessel.
Hydrolysis: Breakdown of complex organic molecules into simpler forms.
I
Influent: Untreated wastewater entering a treatment process.
IRR: Internal Recycle Ratio - recycle from aerobic to anoxic zone.
K
KLa: Oxygen transfer coefficient - rate of oxygen transfer.
Kinetics: Study of reaction rates in biological processes.
L
Lamella: Inclined plate settler for enhanced settling.
Loading Rate: Mass or volume applied per unit time or area.
M
MBR: Membrane Bioreactor - activated sludge with membrane separation.
MBBR: Moving Bed Biofilm Reactor - carriers for attached growth.
MLSS: Mixed Liquor Suspended Solids - biomass concentration in aeration tank.
MLVSS: Mixed Liquor Volatile Suspended Solids - organic portion of MLSS.
N
N2O: Nitrous oxide - potent greenhouse gas from wastewater treatment.
Nitrification: Biological oxidation of ammonia to nitrate.
NOB: Nitrite Oxidizing Bacteria - convert NO2 to NO3.
O
OLR: Organic Loading Rate - organic mass applied per unit volume per day.
ORP: Oxidation-Reduction Potential - measure of electron activity.
OUR: Oxygen Uptake Rate - rate of oxygen consumption by biomass.
P
PAO: Phosphorus Accumulating Organisms - bacteria that store polyphosphate.
PE: Population Equivalent - loading equivalent to one person.
PFR: Plug Flow Reactor - reactor with minimal longitudinal mixing.
pH: Measure of hydrogen ion concentration (acidity/alkalinity).
PID: Proportional-Integral-Derivative controller.
R
RAS: Return Activated Sludge - sludge returned from clarifier to aeration.
rbCOD: Readily biodegradable COD - quickly utilized organic matter.
S
SBR: Sequencing Batch Reactor - fill-and-draw batch treatment.
SCADA: Supervisory Control and Data Acquisition.
SOR: Surface Overflow Rate - flow per unit clarifier area.
SRT: Solids Retention Time (Sludge Age) - average time biomass remains in system.
SVI: Sludge Volume Index - settling characteristic indicator.
T
TKN: Total Kjeldahl Nitrogen - ammonia plus organic nitrogen.
TN: Total Nitrogen - all forms of nitrogen.
TP: Total Phosphorus - all forms of phosphorus.
TSS: Total Suspended Solids - filterable solids in wastewater.
U
UASB: Upflow Anaerobic Sludge Blanket reactor.
UV: Ultraviolet disinfection.
V
VFA: Volatile Fatty Acids - short-chain organic acids (acetate, propionate).
VSS: Volatile Suspended Solids - organic portion of suspended solids.
W
WAS: Waste Activated Sludge - excess sludge removed from the process.
Weir: Overflow structure controlling liquid level.
Y
Y (Yield): Biomass produced per unit substrate consumed.
Unit Abbreviations
| Abbreviation | Meaning |
|---|---|
| d | days |
| h | hours |
| L | liters |
| m³ | cubic meters |
| mg/L | milligrams per liter |
| ML/d | megaliters per day |
| m³/d | cubic meters per day |
| kWh | kilowatt-hours |
| kg | kilograms |
| PE | population equivalent |