the nitrification step is preceded by a pretreatment sequence (i.e., preliminary
treatment, primary treatment, and secondary treatment). Possible secondary treatment may be (a) biological secondary treatment, such as activated sludge, trickling filter, roughing filter, plus secondary clarification; or (b) physicochemical
secondary treatment, such as chemical precipitation/coagulation plus secondary
clarification. Low BOD (i.e., BOD 5 /TKN ratio of less than 3) in the secondary
effluent will assure a high concentration of nitrifiers (Nitrosomonas and
Nitrobacter) in the nitrification biomass. The most common separate stage
nitrification process is the plug flow suspended growth configuration with clarification. In this process, pretreatment effluent (i.e., nitrification influent) is pH
adjusted as required, and aerated, in a plug flow mode. Because the carbonaceous
demand is low, nitrifiers predominate. A clarifier (either sedimentation clarifier or
flotation clarifier) follows aeration, and nitrification sludge is returned to the
aeration tank. A possible modification is the use of pure oxygen in place of
conventional aeration during the plug flow operation.
Nitrifier (nitrifying bacteria) Bacteria that are capable of oxidizing nitrogenous
material, such as Nitrobacter and Nitrosomonas.
Nitrifying bacteria Bacteria that change the ammonia and organic nitrogen in
wastewater into oxidized nitrogen (usually nitrate).
Nitrite (NO 2 ) It is an intermediate oxygenated form of nitrogen
Nitrite Lock Incomplete nitrification resulting in excess nitrite levels that react with
chlorine. Also known as “chlorine sponge.”
Nitrobacter It is a group of nitrifying bacteria that oxidize nitrite to nitrate.
Nitrogen (N) N is an essential nutrient that is often present in wastewater as
ammonia, nitrite, nitrate, and organic nitrogen. The sum of these is expressed
as total nitrogen.
Nitrogen cycle (a) It is a chemical transformation cycle of nitrogen through various
stages of decomposition and assimilation. (b) The natural circulation of nitrogen
among the atmosphere, plants, animals, and microorganisms that live in soil and
water. Nitrogen takes on a variety of chemical forms throughout the nitrogen
cycle, including nitrous oxide (N 2 O) and nitrogen oxides (NOx).
Nitrogen gas (N 2 ) Gaseous form of nitrogen, N, also called atmospheric nitrogen. It
comprises approximately 79% of atmospheric gas.
Nitrogen oxides (NOx) Gases consisting of one molecule of nitrogen and varying
numbers of oxygen molecules. Nitrogen oxides are produced in the emissions of
vehicle exhausts and from power stations. In the atmosphere, nitrogen oxides can
contribute to formation of photochemical ozone (smog), can impair visibility, and
have health consequences; they are thus considered pollutants.
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.
12 Glossary of Natural Resources and Environmental Pollution Control
467
treatment, primary treatment, and secondary treatment). Possible secondary treatment may be (a) biological secondary treatment, such as activated sludge, trickling filter, roughing filter, plus secondary clarification; or (b) physicochemical
secondary treatment, such as chemical precipitation/coagulation plus secondary
clarification. Low BOD (i.e., BOD 5 /TKN ratio of less than 3) in the secondary
effluent will assure a high concentration of nitrifiers (Nitrosomonas and
Nitrobacter) in the nitrification biomass. The most common separate stage
nitrification process is the plug flow suspended growth configuration with clarification. In this process, pretreatment effluent (i.e., nitrification influent) is pH
adjusted as required, and aerated, in a plug flow mode. Because the carbonaceous
demand is low, nitrifiers predominate. A clarifier (either sedimentation clarifier or
flotation clarifier) follows aeration, and nitrification sludge is returned to the
aeration tank. A possible modification is the use of pure oxygen in place of
conventional aeration during the plug flow operation.
Nitrifier (nitrifying bacteria) Bacteria that are capable of oxidizing nitrogenous
material, such as Nitrobacter and Nitrosomonas.
Nitrifying bacteria Bacteria that change the ammonia and organic nitrogen in
wastewater into oxidized nitrogen (usually nitrate).
Nitrite (NO 2 ) It is an intermediate oxygenated form of nitrogen
Nitrite Lock Incomplete nitrification resulting in excess nitrite levels that react with
chlorine. Also known as “chlorine sponge.”
Nitrobacter It is a group of nitrifying bacteria that oxidize nitrite to nitrate.
Nitrogen (N) N is an essential nutrient that is often present in wastewater as
ammonia, nitrite, nitrate, and organic nitrogen. The sum of these is expressed
as total nitrogen.
Nitrogen cycle (a) It is a chemical transformation cycle of nitrogen through various
stages of decomposition and assimilation. (b) The natural circulation of nitrogen
among the atmosphere, plants, animals, and microorganisms that live in soil and
water. Nitrogen takes on a variety of chemical forms throughout the nitrogen
cycle, including nitrous oxide (N 2 O) and nitrogen oxides (NOx).
Nitrogen gas (N 2 ) Gaseous form of nitrogen, N, also called atmospheric nitrogen. It
comprises approximately 79% of atmospheric gas.
Nitrogen oxides (NOx) Gases consisting of one molecule of nitrogen and varying
numbers of oxygen molecules. Nitrogen oxides are produced in the emissions of
vehicle exhausts and from power stations. In the atmosphere, nitrogen oxides can
contribute to formation of photochemical ozone (smog), can impair visibility, and
have health consequences; they are thus considered pollutants.
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.
12 Glossary of Natural Resources and Environmental Pollution Control
467