Activated sludgeAerated wastewater with a suspended biomass.
Aerobic ConditionWhere oxygen is present.
Ammonia Should be called ammoniacal nitrogen.
BODBiochemical oxygen demand: the amount of dissolved oxygen consumed by microbial activity over usually a 5-day test at 20° C (BOD).
Biofilm A film of biomass or microbial cells attached to a surface usually submerged.
BAF  Biological Aerated Filter that contains a submerged medium of a high surface area which is aerated. The excess biomass is cleaned or back washed by some method.
BFBiological filter or trickling filter.  This is usually a circular tank filled with media and a distribution system dispersing wastewater over the media.
CesspoolAn underground watertight tank without outflow used for collecting domestic wastewater. It is a watertight vessel that stores the raw sewage until collected by a tanker.
CODChemical Oxygen Demand is the amount of oxygen consumed by the chemical oxidation of the matter present in the wastewater sample.
CrustAccumulated material that collects on top of the primary liquor and which is removed when the system is de-sludged.
DesludgingMethod of removing by suction tanker the accumulated crust, sludge and deleterious material. Sludge removal reduces BOD loading.
DWFDry Weather Flow is the average daily flow received by the wastewater plant in a day to have originated directly from the premise connected to the plant.
EA/SEPA/EHSEnvironmental Regulators (Environment Agency/Scottish Environment Protection Agency/ Environment and Heritage Service Northern Ireland).
EutrophicationEnrichment of a watercourse or body by nutrients mainly phosphates and nitrates that usually leads to deterioration in the water quality, especially bacterial, algal and/or plant growth.
Full flow to treatmentThe maximum flow a wastewater plant can treat and is usually expressed as a maximum flow for a set number of hours not repeated more than twice a day.
Humus tankA settlement tank that follows secondary treatment.
Mixed liquorThe mixture of microbial solids and wastewater present in activated sludge aeration vessels.
Organic loadingThe amount of BOD present in the wastewater expressed as grams or kilograms per day.
Per capita volume and loadsThe wastewater volume in litres per person per day with the organic and ammonia load expressed in grams.
Population equivalent (pe)The notional value is equivalent to a domestic resident usually used for comparisons or sizing a treatment plant which receives some non-domestic wastewater.
ReedbedA gravel bed with reeds planted to provide some form of additional treatment.
RBCRotating biological contactor is a treatment plant that has discs that rotate in, but which are not completely submerged in, the settled effluent. The biological treatment takes place on the discs.
Septic tankA compartmentalised settling tank that provides a limited amount of anaerobic digestion.
Sequencing batch reactorA treatment process that undergoes a filling, aeration (biomass and wastewater treatment), settlement and discharge phases.
Submerged aerated filter (SAF) A fixed film treatment process in which the media is submerged in the effluent and a mechanical device introduces oxygen.
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