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Glossary N O P R

Nitrate sensitive area
a defined area, designated by statutory order, within which measures are taken to minimise the leaching of nitrates from agriculture into groundwater

Nitrate (NO3-)
the most oxidised form of nitrogen; formed from the oxidation of ammonia by aerobic bacteria; present in fertiliser; the preferred form of nitrogen in discharges to rivers

Nitrifying bacteria
aerobic bacteria that convert ammonia (NH3) into nitrate (NO3-)

Oil interceptor
used to intercept rainwater or spillages contaminated with oil and to retain the liquid for subsequent separation

Oocysts
persistent reproductive spores of Cryptosporidium; excreted by infected animals and spread in unfiltered water; highly resistant to chlorine but destroyed by heat or ozone

Organic
substances such as proteins, sugars, wood and plastics with molecular structures containing carbon-hydrogen (C-H) bonds

Organochlorines
organic compounds containing chlorine, including PCBs, DDT and lindane; accumulate in fatty tissue and may be toxic

Oxidation
the chemical or biochemical change that occurs when a substance combines with oxygen, for example during combustion and respiration; the release of carbon dioxide and energy from organic compounds

Oxygen system
injects oxygen into liquid effluent; increases aerobic microbial activity and the rate of removal of BOD, COD and ammoniacal nitrogen

Ozone (O3)
a naturally occurring unstable form of oxygen; attenuates harmful ultraviolet light in the stratosphere; a pollutant in the atmosphere at ground level; a powerful oxidising agent and disinfectant

Ozoniser
equipment that generates ozone from oxygen or air by electrical discharge; used in the treatment and disinfection of water and wastewater

Packed tower scrubber
cleans gases with a scrubbing liquor as they pass through inert media; removes soluble and noxious gases and mist droplets larger than 5 m

PCBs
polychlorinated biphenyls; very persistent, toxic substances, stored in fatty tissue; previously widely used as fire-resistant dielectric fluids in transformers and capacitors; now prohibited

Pentachlorophenol (PCP)
a powerful biocide, used to preserve cotton and wood; toxic and persistent; release to the environment now heavily restricted

pH
a logarithmic scale (0-14) that reflects acidity or alkalinity; pH 7 indicates neutrality; acidic solutions have lower pH values; alkaline solutions have higher values

Plate scrubbers
remove dust, noxious gases and odours from gaseous emissions by passing them through perforated plates flooded with scrubbing liquor

Pollutant
a chemical or substance that causes harm in the environment

Polychlorinated biphenyls
see PCBs

Polyelectrolytes
natural or synthetic water-soluble macromolecules that assist in the flocculation of dispersed solids

Potable water
water of a quality suitable for drinking

Reed Bed

Managed wetlands used for the treatment of wastewaters; commonly planted with phragmites australis and other species to facilitate BOD removal below soil surface

Red List
a list used in the UK that identifies the most persistent and toxic substances so that their discharge to water and accumulation in living organisms may be strictly controlled

Reverse osmosis
a high pressure filtration system that uses selectively permeable membranes with extremely small pores to separate ions and particles

Rotary scrubber
a device that separates particulate contamination from a gas stream by impaction onto a wet rotor or into a fine spray of scrubbing liquor

Rotating biological contactor
an aerobic treatment system that rotates plastic media with fixed microbial film alternately through liquid effluent and air to reduce the BOD value

2006 Oasis Environmental Ltd