Preliminary effluent: The effluent from a preliminary treatment system (i.e., bar
screen, comminutor, and grit chamber) by which most of large objects, such as
rocks, logs and cans, grit, etc., in raw wastewater have been removed.
Preliminary treatment: It is the first treatment step or preliminary step of either a
conventional wastewater treatment system or an independent physicochemical
treatment system. Preliminary treatment consists of bar screen, comminutor, and
grit chamber mainly for removing large objects, such as rocks, logs and cans, grit,
etc., from raw wastewater. Comminutor is an option depending on the nature and
characteristics of raw wastewater.
Primary effluent: The effluent from a primary treatment system (either primary
sedimentation clarification or primary flotation clarification) by which most of
total suspended solids in wastewater have been removed.
Primary flotation clarification: It is a unit process or unit operation for the
removal of mainly total suspended solids (settleable solids and floatable solids)
from screened wastewater using a primary flotation clarifier.
Primary flotation clarifier: A dissolved air flotation (DAF) reactor is used to float
total suspended solids (TSS) from screened wastewater by decreasing their
apparent density. DAF consists of saturating a portion or all of the wastewater
feed or a portion of recycled effluent with air at a pressure of 25–90 lb/square inch
(gage). The pressurized wastewater is held at this pressure for 0.5–3 minutes in a
retention tank and then released to atmospheric pressure to the flotation chamber.
The sudden reduction in pressure results in the release of microscopic air bubbles
which attach themselves to TSS and oil particles in the wastewater in the flotation
chamber. This results in agglomeration which, due to the entrained air, has greatly
increased vertical rise rates of about 0.5–2 ft/min. The floated materials rise to the
surface to form a froth layer (float). Specially designed scrapers or other skimming devices continuously remove the froth (or float). The retention time in the
flotation chambers is usually about 20–60 minutes for rectangular flotation
clarifier and about 3–15 minutes for circular flotation clarifier using zerohorizontal velocity design. The effectiveness of dissolved air flotation depends
upon the attachment of bubbles to the suspended solids and/or oil which are to be
removed from the waste stream. The attraction between the air bubble and particle
is primarily a result of the particle surface charge and bubble size distribution.
The more uniform the distribution of water and micro-bubbles, the shallower the
flotation clarifier can be. Generally, the depth of effective flotation units is
between 3 and 9 feet.
Primary sedimentation clarification: It is a unit process or unit operation for the
removal of mainly total suspended solids (settleable solids and floatable solids)
from screened wastewater using a primary sedimentation clarifier.
Primary sedimentation clarifier: It is a tank used to settle mainly total suspended
solids (TSS) from screened raw wastewater by gravity. The main objectives of a
primary sedimentation clarifier are removal of settleable solids by settling them to
the clarifier bottom and removal of floatable solids by skimming them from the
clarifier’s wastewater surface. In a rectangular sedimentation clarifier, the
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153
screen, comminutor, and grit chamber) by which most of large objects, such as
rocks, logs and cans, grit, etc., in raw wastewater have been removed.
Preliminary treatment: It is the first treatment step or preliminary step of either a
conventional wastewater treatment system or an independent physicochemical
treatment system. Preliminary treatment consists of bar screen, comminutor, and
grit chamber mainly for removing large objects, such as rocks, logs and cans, grit,
etc., from raw wastewater. Comminutor is an option depending on the nature and
characteristics of raw wastewater.
Primary effluent: The effluent from a primary treatment system (either primary
sedimentation clarification or primary flotation clarification) by which most of
total suspended solids in wastewater have been removed.
Primary flotation clarification: It is a unit process or unit operation for the
removal of mainly total suspended solids (settleable solids and floatable solids)
from screened wastewater using a primary flotation clarifier.
Primary flotation clarifier: A dissolved air flotation (DAF) reactor is used to float
total suspended solids (TSS) from screened wastewater by decreasing their
apparent density. DAF consists of saturating a portion or all of the wastewater
feed or a portion of recycled effluent with air at a pressure of 25–90 lb/square inch
(gage). The pressurized wastewater is held at this pressure for 0.5–3 minutes in a
retention tank and then released to atmospheric pressure to the flotation chamber.
The sudden reduction in pressure results in the release of microscopic air bubbles
which attach themselves to TSS and oil particles in the wastewater in the flotation
chamber. This results in agglomeration which, due to the entrained air, has greatly
increased vertical rise rates of about 0.5–2 ft/min. The floated materials rise to the
surface to form a froth layer (float). Specially designed scrapers or other skimming devices continuously remove the froth (or float). The retention time in the
flotation chambers is usually about 20–60 minutes for rectangular flotation
clarifier and about 3–15 minutes for circular flotation clarifier using zerohorizontal velocity design. The effectiveness of dissolved air flotation depends
upon the attachment of bubbles to the suspended solids and/or oil which are to be
removed from the waste stream. The attraction between the air bubble and particle
is primarily a result of the particle surface charge and bubble size distribution.
The more uniform the distribution of water and micro-bubbles, the shallower the
flotation clarifier can be. Generally, the depth of effective flotation units is
between 3 and 9 feet.
Primary sedimentation clarification: It is a unit process or unit operation for the
removal of mainly total suspended solids (settleable solids and floatable solids)
from screened wastewater using a primary sedimentation clarifier.
Primary sedimentation clarifier: It is a tank used to settle mainly total suspended
solids (TSS) from screened raw wastewater by gravity. The main objectives of a
primary sedimentation clarifier are removal of settleable solids by settling them to
the clarifier bottom and removal of floatable solids by skimming them from the
clarifier’s wastewater surface. In a rectangular sedimentation clarifier, the
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153