Installations of motor-driven, rotary-type distributors have been used in filters
ranging in size from 7.6 to 46 m (25–150 ft) in diameter.
There is a single conduit to convey the wastewater from primary settling tank to
the distributor. Methods of conveying wastewater include gravity feed, dosing
siphons, and pumping. When the filter is not designed for continuous dosing, the
distributor is usually preceded by a pump or dosing tank and siphon.
All hydraulic factors involving proper distribution of wastewater on the filters
should be carefully calculated. A minimum head of 0.6 m between low water level in
siphon chamber and center of distributor arms is desirable. The head requirements of
distributors are set by the manufacturers. The major head loss is the difference in
elevation from the lowest water surface in the main underdrain channel. A minimum
clearance of 0.15 m between distributor arms and filter media shall be provided. The
head loss approximates 2.4 m (8 ft) for a filter 1.9 m (6 ft) deep and can be
considerably greater for a deeper synthetic media filter.
It is important to know that bead losses chargeable to the trickling filter usually
exceed the sum of all other head losses in the entire wastewater treatment plant.
Compared with the activated sludge process, the trickling filter process requires
much higher drop in static head, but requires less power.
Most trickling filter plants constructed in this country are circular and have rotary
distributors. The majority of filters have reinforced concrete walls around the
circumference, usually 0.2–0.3 m thick. The side walls are extended about 1 m to
provide wind breaks.
The filter media may be crushed rock, slag, redwood, or specially manufactured
synthetic plastic material. The media shall be durable, be resistant to spalling or
flaking, and be chemically and biologically inert. The characteristics of various filter
media are shown in Table 3.6 [130].
Underdrains with semicircular inverts or equivalent should be provided, and the
underdrainage system shall cover the entire floor of the trickling filter. Inlet openings
into the underdrains shall have an unsubmerged gross combined area equal to at least
15% of the surface area of the filter. The slope of underdrains shall be at least 1%.
Effluent channels shall be designed to produce a minimum velocity of 0.6 m/s (2 ft/s)
at average daily wastewater flow to the filter.
Ventilation of filter is important in maintaining the aerobic conditions necessary
to secure effective biological treatment; therefore, adequate passageways at the
bottom of the filters must be provided to permit free flow of air. Installation of
vent stacks on the filter periphery, ventilating manholes, and discharge of filter
effluent to the subsequent sedimentation basin in an open channel or partly filled
pipes are methods employed to insure adequate ventilation. The Ten State Standards
[87] require that inlet openings into the filter underdrains have an unsubmerged gross
combined area equal to at least 15% of the surface area of the filter and that the size
of drains, channels, and pipe be such that no more than 50% of their cross-sectional
area will be submerged under the design hydraulic loading. Synthetic media manufacturers often recommend 0.1 m
2 (1 ft
2 ) of ventilating area for each 3–4.6 m of
plastic media filter’s tower periphery for domestic wastewater. Consideration may
also be given to a forced ventilation system.
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L. K. Wang et al.
ranging in size from 7.6 to 46 m (25–150 ft) in diameter.
There is a single conduit to convey the wastewater from primary settling tank to
the distributor. Methods of conveying wastewater include gravity feed, dosing
siphons, and pumping. When the filter is not designed for continuous dosing, the
distributor is usually preceded by a pump or dosing tank and siphon.
All hydraulic factors involving proper distribution of wastewater on the filters
should be carefully calculated. A minimum head of 0.6 m between low water level in
siphon chamber and center of distributor arms is desirable. The head requirements of
distributors are set by the manufacturers. The major head loss is the difference in
elevation from the lowest water surface in the main underdrain channel. A minimum
clearance of 0.15 m between distributor arms and filter media shall be provided. The
head loss approximates 2.4 m (8 ft) for a filter 1.9 m (6 ft) deep and can be
considerably greater for a deeper synthetic media filter.
It is important to know that bead losses chargeable to the trickling filter usually
exceed the sum of all other head losses in the entire wastewater treatment plant.
Compared with the activated sludge process, the trickling filter process requires
much higher drop in static head, but requires less power.
Most trickling filter plants constructed in this country are circular and have rotary
distributors. The majority of filters have reinforced concrete walls around the
circumference, usually 0.2–0.3 m thick. The side walls are extended about 1 m to
provide wind breaks.
The filter media may be crushed rock, slag, redwood, or specially manufactured
synthetic plastic material. The media shall be durable, be resistant to spalling or
flaking, and be chemically and biologically inert. The characteristics of various filter
media are shown in Table 3.6 [130].
Underdrains with semicircular inverts or equivalent should be provided, and the
underdrainage system shall cover the entire floor of the trickling filter. Inlet openings
into the underdrains shall have an unsubmerged gross combined area equal to at least
15% of the surface area of the filter. The slope of underdrains shall be at least 1%.
Effluent channels shall be designed to produce a minimum velocity of 0.6 m/s (2 ft/s)
at average daily wastewater flow to the filter.
Ventilation of filter is important in maintaining the aerobic conditions necessary
to secure effective biological treatment; therefore, adequate passageways at the
bottom of the filters must be provided to permit free flow of air. Installation of
vent stacks on the filter periphery, ventilating manholes, and discharge of filter
effluent to the subsequent sedimentation basin in an open channel or partly filled
pipes are methods employed to insure adequate ventilation. The Ten State Standards
[87] require that inlet openings into the filter underdrains have an unsubmerged gross
combined area equal to at least 15% of the surface area of the filter and that the size
of drains, channels, and pipe be such that no more than 50% of their cross-sectional
area will be submerged under the design hydraulic loading. Synthetic media manufacturers often recommend 0.1 m
2 (1 ft
2 ) of ventilating area for each 3–4.6 m of
plastic media filter’s tower periphery for domestic wastewater. Consideration may
also be given to a forced ventilation system.
134
L. K. Wang et al.