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Glossary S T U V W


Sand filter
separates suspended solids and associated BOD/COD from liquids by passing the liquid through a bed of sand

equipment that separates solid material from liquid by allowing the liquid to pass through constrictions (the screen) of chosen size

Septic tank
container that receives untreated sewage, holds back floating scum and retains and digests heavy solids but allows clarified liquor to proceed forward for further treatment or discharge

Settlement tank
container that allows sufficient retention time for the separation of organic and inorganic solids from liquid and produces sludge and clarified liquor both of which may receive further treatment

liquid effluent from domestic and industrial activity

the wet solids that can be settled from an untreated liquid effluent (primary sludge); or from aerobically treated effluent (secondary sludge)

mixture of urine, faeces and wash water from cattle or pig rearing

Soil washing
water-based volume reduction process in which contaminated soil or dredgings are separated into a small contaminated fraction, for further treatment or disposal, and a larger cleaned fraction

Special waste
waste that contains substances considered to be dangerous to life as listed in the Control of Pollution (Special Waste) Regulations 1980; applies within the UK

Static tubular aerator
a system in which air is blown into vertical tubes submerged in a liquid, promoting mixing and oxygen transfer

Submerged aerated filter
a device in which highly aerated effluent flows through inert media that is completely submerged; fixed microbial film reduces the BOD and ammoniacal content of the effluent

Submerged biological contactor
an aerobic treatment system in which plastic media that is largely submerged in effluent is rotated by rising air, the fixed microbial film on the media reducing the BOD value

Submicron particles
particles of less than 1m in size, present in smoke and fumes

Sulphur dioxide (SO2)Sulphur dioxide (SO2)
toxic gas produced during the combustion of sulphur compounds in fossil fuels; component of acid rain

Surface aerator
equipment in which blades or vanes rotate about a vertical or horizontal shaft and entrain air to mix and aerate wastewater

Suspended solids
solids of organic and inorganic origin present in liquid effluents; concentration in (mg/l) measured by filtration followed by drying at 105 -C

Thermal oxidation
high temperature incineration of pollutants such as VOCs and odours in gas streams

Trickling filter
a bed of gravel or pebble media through which clarified effluent percolates and microbial activity removes BOD, suspended solids and ammoniacal nitrogen

a measure of the cloudiness of a liquid that is caused by the presence of fine suspended solids

the separation from a liquid of particles of 0005-01 m in size by pumping the liquid through a synthetic membrane at high pressure

Ultrapure water
water from which most other materials have been removed, producing a resistivity of at least 18 M-cm, and making it sufficiently pure for the most exacting microelectronic, pharmaceutical and medical uses

Ultraviolet light system
a disinfection system in which light of 254 nm, produced by mercury lamps, damages microorganisms by disrupting their genetic material

UV ozone
a powerful wastewater treatment process employing ozone in solution and ultraviolet light; oxidises COD and toxic substances, removes colour and disinfects

Vapour extraction
a technique that makes use of a partial vacuum to remove volatile and semi-volatile contamination, such as hydrocarbons, from soils

Venturi aerator
a submerged jet aeration device in which the liquid to be aerated is pumped through a nozzle within a larger diameter tube, causing air entrainment and vigorous liquid mixing

Venturi scrubber
a device that removes submicron particles and reactive trace gases from gas streams by passing the gas at high velocity through the scrubbing liquor ensuring vigorous mixing

Volatile organic compounds (VOCs)
substances such as solvents that are liquid at room temperature, but vaporise significantly and take part in the generation of ozone pollution in the lower atmosphere

Waste minimisation
the analysis and revision of the use of materials, processes, equipment and procedures in order to reduce the unnecessary use of energy and resources, to reduce the generation of effluents and wastes and to recycle where practical

Waste incineration
incineration of waste at high temperatures in two stages to promote efficient combustion to an ash and carbon dioxide

Wet air oxidation
a process that treats waste water containing high strength or hazardous organic chemicals by a combination of high temperature and pressure that creates highly reactive hydroxyl radicals

2006 Oasis Environmental Ltd