Activated sludge Aerated wastewater with a suspended biomass.
Aerobic Condition Where oxygen is present.
Ammonia  Should be called ammoniacal nitrogen.
BOD Biochemical 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.
BF Biological filter or trickling filter.  This is usually a circular tank filled with media and a distribution system dispersing wastewater over the media.
Cesspool An 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.
COD Chemical Oxygen Demand is the amount of oxygen consumed by the chemical oxidation of the matter present in the wastewater sample.
Crust Accumulated material that collects on top of the primary liquor and which is removed when the system is de-sludged.
Desludging Method of removing by suction tanker the accumulated crust, sludge and deleterious material. Sludge removal reduces BOD loading.
DWF Dry 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/EHS Environmental Regulators (Environment Agency/Scottish Environment Protection Agency/ Environment and Heritage Service Northern Ireland).
Eutrophication Enrichment 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 treatment The 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 tank A settlement tank that follows secondary treatment.
Mixed liquor The mixture of microbial solids and wastewater present in activated sludge aeration vessels.
Organic loading The amount of BOD present in the wastewater expressed as grams or kilograms per day.
Per capita volume and loads The 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.
Reedbed A gravel bed with reeds planted to provide some form of additional treatment.
RBC Rotating 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 tank A compartmentalised settling tank that provides a limited amount of anaerobic digestion.
Sequencing batch reactor A 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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