The accumulated float (thickened biosolids) at solids content of 2–3% is removed by
the spiral scoop and discharged to the biosolids handling system via the central
sludge well [8, 16, 17].
As the biosolids rise to the top, the clarified water flows downward through the
filter bed. The bottom of the tank is composed of multisections of sand filter
segments. Each of the 27 segments is individually isolated and backwashed, while
the remaining parts of the filter are on line. The filter media consist of 0.28 m deep
high-grade silica sand. The effective size and uniformity coefficient for the sand are
0.35 mm and 1.55, respectively. The backwashing is uniformly extended over the
complete filtering time. This enables the use of a smaller backwash pump, and
minimizes or even eliminates any overloading on the unit that may result from the
recycling of decanted backwash water [23].
The backwash hood, pump, and motor are mounted on a carriage that rotates on
the upper rim of the main tank. The filter segments are set up for backwashing at a
predetermined time interval that can be adjusted depending on head loss and the
accumulation of solids. The backwash water containing the solids captured by the
sand is recirculated back to the flocculator. The clearwell is located immediately
below the sand bed. The clear water is utilized directly for backwash as needed.
The filter assures the removal of any solids not removed in the flocculation and
flotation stages, the flocculation is enhanced by the recirculated backwash solids,
and the filtration is protected by the removal of solids in the flotation stage. The
combination of the three operations in a single tank reduces the head loss and
turbulence between stages, thus increasing the efficiency of removal of the fragile
flocculated solids. No storage is required for the clarified water or the backwash
water. Discharge of backwash water is eliminated, and the only discharge is the float,
thickened biosolids suitable for handling, thus possibly eliminating the necessity for
a biosolids thickener [24–26].
Fig. 2.1 Flotation/filtration
cell (FF-Cell)
56
N. K. Shammas et al.
the spiral scoop and discharged to the biosolids handling system via the central
sludge well [8, 16, 17].
As the biosolids rise to the top, the clarified water flows downward through the
filter bed. The bottom of the tank is composed of multisections of sand filter
segments. Each of the 27 segments is individually isolated and backwashed, while
the remaining parts of the filter are on line. The filter media consist of 0.28 m deep
high-grade silica sand. The effective size and uniformity coefficient for the sand are
0.35 mm and 1.55, respectively. The backwashing is uniformly extended over the
complete filtering time. This enables the use of a smaller backwash pump, and
minimizes or even eliminates any overloading on the unit that may result from the
recycling of decanted backwash water [23].
The backwash hood, pump, and motor are mounted on a carriage that rotates on
the upper rim of the main tank. The filter segments are set up for backwashing at a
predetermined time interval that can be adjusted depending on head loss and the
accumulation of solids. The backwash water containing the solids captured by the
sand is recirculated back to the flocculator. The clearwell is located immediately
below the sand bed. The clear water is utilized directly for backwash as needed.
The filter assures the removal of any solids not removed in the flocculation and
flotation stages, the flocculation is enhanced by the recirculated backwash solids,
and the filtration is protected by the removal of solids in the flotation stage. The
combination of the three operations in a single tank reduces the head loss and
turbulence between stages, thus increasing the efficiency of removal of the fragile
flocculated solids. No storage is required for the clarified water or the backwash
water. Discharge of backwash water is eliminated, and the only discharge is the float,
thickened biosolids suitable for handling, thus possibly eliminating the necessity for
a biosolids thickener [24–26].
Fig. 2.1 Flotation/filtration
cell (FF-Cell)
56
N. K. Shammas et al.