Nitrogen cycle: It is a chemical transformation cycle of nitrogen through various
stages of decomposition and assimilation.
Nitrogen gas (N 2 ): Gaseous form of nitrogen, N, also called atmospheric nitrogen.
It comprises approximately 79% of atmospheric gas.
Nitrogenous biochemical oxygen demand (NBOD): The quantitative measure of
the amount of oxygen required for the biological oxidation of nitrogenous
material, such as ammonia nitrogen and organic nitrogen (measured by
subtracting carbonaceous BOD from total BOD values).
Nitrosomonas: A genus of nitrifying bacteria that oxidize ammonia to nitrite.
Nocardia: It is a group of irregularly bent, short-branching filamentous organisms
that cause dense dark foam in aeration basins. Associated with high fats, oils, and
greases. Easily identified under a microscope.
Nutrient: A substance that is taken in by organisms and promotes growth. Carbon,
nitrogen, and phosphorus are essential nutrients to most aquatic organisms.
Organic nitrogen: It is an organic nutrient containing nitrogen which is chemically
bound in organic molecules such as proteins, amines, and amino acids. It is
calculated by subtracting the ammonia nitrogen analysis results from total
Kjeldahl nitrogen analysis results.
Organic phosphate: (a) It is a molecule of phosphate combined with an organic
compound. Total phosphorus includes orthophosphate, polyphosphate, and
organic phosphate. (b) It is an organic phosphorus originating from organic
sources, such as body and food waste, and sometimes industrial sources. Some
can biologically decompose into inorganic orthophosphate; other types are
non-biodegradable and will pass through the wastewater system without
treatment.
Organic: A volatile, combustible, or biodegradable compound containing carbon
bound with other elements.
Orthophosphate: It is an inorganic nutrient containing phosphorus which is
required for plant and animal growth. An inorganic, soluble form of phosphorus
that is readily available to plants and animals without further breakdown and
accounts for 70–90% of total phosphorus in wastewater. The easiest form of
phosphorus that can be treated chemically. Total phosphorus includes orthophosphate, polyphosphate, and organic phosphate.
Oxic: It is an environmental condition in which an aquatic environment contains
dissolved oxygen, usually in the range of 1.5–2.0 mg/L.
Oxidation ditch: It is a ring-shaped channel suspended-growth biological process
system similar to extended aeration process for mainly carbonaceous oxidation
and nitrification. It was developed to minimize waste activated sludge production
through endogenous decay of the sludge mass. It is equipped with mechanical
aeration devices, such as mechanical brush aerators surface aerators and jet
aerator devices, to aerate and pump the wastewater. Screened wastewater enters
the ditch is aerated and circulates at about 0.8–1.2 ft/sec. The economics of
oxidation ditches appear most favorable when the solids retention time (SRT) is
long, particularly where nitrification is required. When both nitrification and
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151
stages of decomposition and assimilation.
Nitrogen gas (N 2 ): Gaseous form of nitrogen, N, also called atmospheric nitrogen.
It comprises approximately 79% of atmospheric gas.
Nitrogenous biochemical oxygen demand (NBOD): The quantitative measure of
the amount of oxygen required for the biological oxidation of nitrogenous
material, such as ammonia nitrogen and organic nitrogen (measured by
subtracting carbonaceous BOD from total BOD values).
Nitrosomonas: A genus of nitrifying bacteria that oxidize ammonia to nitrite.
Nocardia: It is a group of irregularly bent, short-branching filamentous organisms
that cause dense dark foam in aeration basins. Associated with high fats, oils, and
greases. Easily identified under a microscope.
Nutrient: A substance that is taken in by organisms and promotes growth. Carbon,
nitrogen, and phosphorus are essential nutrients to most aquatic organisms.
Organic nitrogen: It is an organic nutrient containing nitrogen which is chemically
bound in organic molecules such as proteins, amines, and amino acids. It is
calculated by subtracting the ammonia nitrogen analysis results from total
Kjeldahl nitrogen analysis results.
Organic phosphate: (a) It is a molecule of phosphate combined with an organic
compound. Total phosphorus includes orthophosphate, polyphosphate, and
organic phosphate. (b) It is an organic phosphorus originating from organic
sources, such as body and food waste, and sometimes industrial sources. Some
can biologically decompose into inorganic orthophosphate; other types are
non-biodegradable and will pass through the wastewater system without
treatment.
Organic: A volatile, combustible, or biodegradable compound containing carbon
bound with other elements.
Orthophosphate: It is an inorganic nutrient containing phosphorus which is
required for plant and animal growth. An inorganic, soluble form of phosphorus
that is readily available to plants and animals without further breakdown and
accounts for 70–90% of total phosphorus in wastewater. The easiest form of
phosphorus that can be treated chemically. Total phosphorus includes orthophosphate, polyphosphate, and organic phosphate.
Oxic: It is an environmental condition in which an aquatic environment contains
dissolved oxygen, usually in the range of 1.5–2.0 mg/L.
Oxidation ditch: It is a ring-shaped channel suspended-growth biological process
system similar to extended aeration process for mainly carbonaceous oxidation
and nitrification. It was developed to minimize waste activated sludge production
through endogenous decay of the sludge mass. It is equipped with mechanical
aeration devices, such as mechanical brush aerators surface aerators and jet
aerator devices, to aerate and pump the wastewater. Screened wastewater enters
the ditch is aerated and circulates at about 0.8–1.2 ft/sec. The economics of
oxidation ditches appear most favorable when the solids retention time (SRT) is
long, particularly where nitrification is required. When both nitrification and
3 Biological Processes
151