efficient design is made possible by the use of the space (water head) above the filter
for flotation, a space or water head, which, in any case, is necessary for filtration.
Two more features were used to reduce space requirements [10, 16, 17]:
1. A static hydraulic flocculator was built into the central portion of the tank to
combine a third process in the single tank.
2. A segmented continuous backwash filter was used to eliminate requirements for
large tanks for clearwell and backwash storage. Therefore, the end result replaces
a conventional process requiring five separate tanks with a single, compact, and
cheaper unit.
The aim of this chapter is to document six applications to illustrate the versatility
and effectiveness of the flotation/filtration cell, to demonstrate the performance of
the compact unit in secondary and tertiary treatment of various wastewater effluents,
and to illustrate the system’s usefulness for wastewater reclamation, recycling, and
reuse. The five applications are as follows [18–21]:
1. Treatment of primary municipal wastewater effluent at Hoboken, NJ., USA
2. Treatment of raw municipal wastewater at Lee, MA, USA
3. Tertiary treatment of activated sludge effluent at Oak Meadows STP, Licking
County, OH, USA
4. Tertiary treatment of RBC Effluent at Jimmy Peak, MA, USA
5. Tertiary treatment of trickling filter effluent at Norwalk, OH, USA
6. Tertiary treatment of lagoons effluent at Arpin, WI, USA
2 Flotation/Filtration Cell
The flotation/filtration pilot plant used in these applications is shown in Fig. 2.1 and
its details are illustrated in Fig. 2.2. The flotation-filtration tank is 1.5 m in diameter
and has a design nominal capacity of 150 L/min of wastewater flow [18].
The influent flow is mixed with flocculant and coagulant chemicals, and gently
flocculated in the central zone of the tank. The backwash recycled from the filter is
mixed with the inflowing water at the flocculator inlet. This eliminates the need for
disposal of the backwash separately, and also, in some cases, provides a “seed” of
solids for better floc formation. The floc size required for removal of the solids is
smaller than that required for settling. This reduces the space requirement for
flocculation [10, 22].
When the flocculated solids reach the upper part of the flocculation zone, they are
mixed with the recycle flow, which contains millions of microscopic (20–100
micron diameter) air bubbles. The air bubbles are generated by injecting air into
recirculated clarified water under pressure (60 psi), followed by rapid decompression
under high shear conditions. The amount of recirculated water used varies depending
on the amount and type of solids to be removed, but it is generally 15–30% of the
incoming flow. The air bubbles attach to the flocculated solids, or are entrapped in
the floc to produce air-solid agglomerate that rapidly rises to the surface of the tank.
2 Water Reclamation
55
for flotation, a space or water head, which, in any case, is necessary for filtration.
Two more features were used to reduce space requirements [10, 16, 17]:
1. A static hydraulic flocculator was built into the central portion of the tank to
combine a third process in the single tank.
2. A segmented continuous backwash filter was used to eliminate requirements for
large tanks for clearwell and backwash storage. Therefore, the end result replaces
a conventional process requiring five separate tanks with a single, compact, and
cheaper unit.
The aim of this chapter is to document six applications to illustrate the versatility
and effectiveness of the flotation/filtration cell, to demonstrate the performance of
the compact unit in secondary and tertiary treatment of various wastewater effluents,
and to illustrate the system’s usefulness for wastewater reclamation, recycling, and
reuse. The five applications are as follows [18–21]:
1. Treatment of primary municipal wastewater effluent at Hoboken, NJ., USA
2. Treatment of raw municipal wastewater at Lee, MA, USA
3. Tertiary treatment of activated sludge effluent at Oak Meadows STP, Licking
County, OH, USA
4. Tertiary treatment of RBC Effluent at Jimmy Peak, MA, USA
5. Tertiary treatment of trickling filter effluent at Norwalk, OH, USA
6. Tertiary treatment of lagoons effluent at Arpin, WI, USA
2 Flotation/Filtration Cell
The flotation/filtration pilot plant used in these applications is shown in Fig. 2.1 and
its details are illustrated in Fig. 2.2. The flotation-filtration tank is 1.5 m in diameter
and has a design nominal capacity of 150 L/min of wastewater flow [18].
The influent flow is mixed with flocculant and coagulant chemicals, and gently
flocculated in the central zone of the tank. The backwash recycled from the filter is
mixed with the inflowing water at the flocculator inlet. This eliminates the need for
disposal of the backwash separately, and also, in some cases, provides a “seed” of
solids for better floc formation. The floc size required for removal of the solids is
smaller than that required for settling. This reduces the space requirement for
flocculation [10, 22].
When the flocculated solids reach the upper part of the flocculation zone, they are
mixed with the recycle flow, which contains millions of microscopic (20–100
micron diameter) air bubbles. The air bubbles are generated by injecting air into
recirculated clarified water under pressure (60 psi), followed by rapid decompression
under high shear conditions. The amount of recirculated water used varies depending
on the amount and type of solids to be removed, but it is generally 15–30% of the
incoming flow. The air bubbles attach to the flocculated solids, or are entrapped in
the floc to produce air-solid agglomerate that rapidly rises to the surface of the tank.
2 Water Reclamation
55