(as the product water), recycles certain amount of activated sludge to the bioreactor, and wastes the excess amount of activated sludge. In the future a MBR may
also be a combination of an attached-growth bioreactor and a membrane filter.
Mixed liquor suspended solids (MLSS): The concentration of suspended solids
present in activated sludge mixed liquor, usually expressed as milligrams per liter
(mg/L).
Mixed liquor volatile suspended solids (MLVSS): The fraction of the suspended
solids in biological reactor’s mixed liquor that can be burned off by combustion at
550
C. or the organic portion of the solids (an estimation of the microorganisms
and food). Usually expressed as milligrams per liter (mg/L).
Mixed liquor: The water containing biosolids in a biological reactor.
Nitrate (NO 3 ): An oxygenated form of nitrogen.
Nitrification: It is a biological process by which ammonia in wastewater is
converted by Nitrosomonas and Nitrobacter to nitrite and then to nitrate in the
presence of oxygen. The biological reactions involved in these conversions may
take place during activated sludge treatment or as a separate stage following the
removal of carbonaceous materials. Separate-stage nitrification may be accomplished via suspended-growth or attached-growth unit processes. In either case,
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.
Nitrification: The process of oxidizing ammonia nitrogen to nitrate in wastewater
by chemical or biological reactions.
Nitrifier (nitrifying bacteria): Bacteria that are capable of oxidizing nitrogenous
material, such as Nitrobacter and Nitrosomonas.
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.
150
L. K. Wang et al.
also be a combination of an attached-growth bioreactor and a membrane filter.
Mixed liquor suspended solids (MLSS): The concentration of suspended solids
present in activated sludge mixed liquor, usually expressed as milligrams per liter
(mg/L).
Mixed liquor volatile suspended solids (MLVSS): The fraction of the suspended
solids in biological reactor’s mixed liquor that can be burned off by combustion at
550
C. or the organic portion of the solids (an estimation of the microorganisms
and food). Usually expressed as milligrams per liter (mg/L).
Mixed liquor: The water containing biosolids in a biological reactor.
Nitrate (NO 3 ): An oxygenated form of nitrogen.
Nitrification: It is a biological process by which ammonia in wastewater is
converted by Nitrosomonas and Nitrobacter to nitrite and then to nitrate in the
presence of oxygen. The biological reactions involved in these conversions may
take place during activated sludge treatment or as a separate stage following the
removal of carbonaceous materials. Separate-stage nitrification may be accomplished via suspended-growth or attached-growth unit processes. In either case,
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.
Nitrification: The process of oxidizing ammonia nitrogen to nitrate in wastewater
by chemical or biological reactions.
Nitrifier (nitrifying bacteria): Bacteria that are capable of oxidizing nitrogenous
material, such as Nitrobacter and Nitrosomonas.
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.
150
L. K. Wang et al.