wastewater flows from one end to the other, and the settled sludge is moved to a
hopper at one end, either by scrapers called “flights” set on parallel chains or by a
single bottom scraper set on a traveling bridge. Floating materials, such as grease
and oil, are collected by a surface skimmer and then removed from the rectangular
sedimentation clarifier. In a circular sedimentation clarifier, the wastewater usually enters in the middle and flows toward the outside edge. Settled sludge is
pushed to the hopper that is in the middle of the circular clarifier’s tank bottom.
Floating material is removed by a surface skimmer connected to the sludge
collector.
Primary treatment: It is an important wastewater treatment step (either primary
sedimentation clarification or primary flotation clarification mainly for removing
total suspended solids from preliminary treatment effluent) after the preliminary
treatment (i.e., bar screen, comminutor, and grit chamber mainly for removing
large objects from raw wastewater), but before secondary treatment (either
biological treatment or physicochemical treatment mainly for removing dissolved
organic/inorganic pollutants from primary effluent).
Protozoan: Small, one-celled animals such as amoebae, ciliates, and flagellates.
Rapid mixing: A water treatment unit process of quickly mixing a chemical
solution uniformly through the process water.
Reduction: A chemical reaction involving the addition of electrons to a chemical
entity.
Return activated sludge (RAS): (a) Settled activated sludge, returned from the
bottom of final sedimentation clarifiers, to mix with incoming raw or primary
effluent; (b) floated activated sludge, returned from the top of flotation clarifiers,
to mix with incoming raw or primary effluent.
Rotating biological contactor (RBC): In a RBC system, a series of closely spaced
circular polystyrene or polyvinyl chloride disks is partially submerged in wastewater. Biological growth (biomass) attached to the surface of the disks. The
biomass is kept in aerobic conditions (if carbonaceous oxidation and nitrification
are intended) or anoxic conditions (if denitrification is intended) by rotation of the
disks. Aerobic RBC is opened, so biomass may utilize the oxygen in the air, while
anoxic RBC for denitrification is normally closed to block off the air. The RBC
effluent discharges to a clarifier (either a sedimentation clarifier or a flotation
clarifier) for solid-water separation, returning sludge, wasting sludge, and clarifier
effluent discharge.
Sandfloat: It is combined circular dissolved air flotation and filtration (DAFF)
clarifier designed by the Lenox Institute of Water Technology (LIWT) and
manufactured by Krofta Engineering Corporation (KEC).
Secondary effluent: The effluent from a secondary treatment step which may be
either (a) biological treatment, such as activated sludge aeration or equivalent
plus secondary clarification, or (b) physicochemical treatment, such as chemical
precipitation/coagulation plus secondary clarification. Secondary treatment step
removes most of dissolved organic/inorganic pollutants from primary effluent.
Since secondary clarification (either secondary sedimentation clarification or
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L. K. Wang et al.
hopper at one end, either by scrapers called “flights” set on parallel chains or by a
single bottom scraper set on a traveling bridge. Floating materials, such as grease
and oil, are collected by a surface skimmer and then removed from the rectangular
sedimentation clarifier. In a circular sedimentation clarifier, the wastewater usually enters in the middle and flows toward the outside edge. Settled sludge is
pushed to the hopper that is in the middle of the circular clarifier’s tank bottom.
Floating material is removed by a surface skimmer connected to the sludge
collector.
Primary treatment: It is an important wastewater treatment step (either primary
sedimentation clarification or primary flotation clarification mainly for removing
total suspended solids from preliminary treatment effluent) after the preliminary
treatment (i.e., bar screen, comminutor, and grit chamber mainly for removing
large objects from raw wastewater), but before secondary treatment (either
biological treatment or physicochemical treatment mainly for removing dissolved
organic/inorganic pollutants from primary effluent).
Protozoan: Small, one-celled animals such as amoebae, ciliates, and flagellates.
Rapid mixing: A water treatment unit process of quickly mixing a chemical
solution uniformly through the process water.
Reduction: A chemical reaction involving the addition of electrons to a chemical
entity.
Return activated sludge (RAS): (a) Settled activated sludge, returned from the
bottom of final sedimentation clarifiers, to mix with incoming raw or primary
effluent; (b) floated activated sludge, returned from the top of flotation clarifiers,
to mix with incoming raw or primary effluent.
Rotating biological contactor (RBC): In a RBC system, a series of closely spaced
circular polystyrene or polyvinyl chloride disks is partially submerged in wastewater. Biological growth (biomass) attached to the surface of the disks. The
biomass is kept in aerobic conditions (if carbonaceous oxidation and nitrification
are intended) or anoxic conditions (if denitrification is intended) by rotation of the
disks. Aerobic RBC is opened, so biomass may utilize the oxygen in the air, while
anoxic RBC for denitrification is normally closed to block off the air. The RBC
effluent discharges to a clarifier (either a sedimentation clarifier or a flotation
clarifier) for solid-water separation, returning sludge, wasting sludge, and clarifier
effluent discharge.
Sandfloat: It is combined circular dissolved air flotation and filtration (DAFF)
clarifier designed by the Lenox Institute of Water Technology (LIWT) and
manufactured by Krofta Engineering Corporation (KEC).
Secondary effluent: The effluent from a secondary treatment step which may be
either (a) biological treatment, such as activated sludge aeration or equivalent
plus secondary clarification, or (b) physicochemical treatment, such as chemical
precipitation/coagulation plus secondary clarification. Secondary treatment step
removes most of dissolved organic/inorganic pollutants from primary effluent.
Since secondary clarification (either secondary sedimentation clarification or
154
L. K. Wang et al.