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CLARIFICATION 7.35

• Sludge extraction
• Drain, washdown, and sample system
• Controls
The treatment cycle begins when previously mixed influent water and coagulant chem-
icals enter the vacuum chamber. With the vacuum pump running and the vacuum release
valve closed, pressure is reduced inside the chamber, causing the water level to rise to a
predetermined level. This level is controlled by a timer that actuates the vacuum release
valve. When the vacuum is released, the water level drops rapidly, causing a surge of wa-
ter to flow into the distribution system. As the water level in the vacuum chamber drops
to the hydraulic grade line of the influent water, the head is dissipated and the surge slows.
A timer then closes the vent valve, and the vacuum pump, which runs continuously, be-
gins evacuating the air to repeat the cycle. This rising and falling of the water level in the
vacuum chamber create the rhythmic, controlled pulsing for which the pulsed blanket clar-
ifier is known. Pulsations create and maintain the sludge blanket in homogeneous sus-
pension critical for efficient solids removal. Pulsations also aid in flocculation created by
the turbulence from the high-velocity flow leaving distribution pipe orifices.
As water enters the sludge blanket and passes upward through it under the forces of
succeeding pulsations, the sludge blanket performs the double tasks of flocculation and
filtration: It serves as a medium that agglomerates the newly formed floc, and it helps
suspended matter and colloidal particles adhere to the floc.
Water exits the sludge blanket into the clarification zone. Because the flow rate is
lower in the clarification zone than in the blanket, particles that escape the blanket settle
back toward the blanket. In the Superpulsator, a trademark of Ondeo-Degremont Inc.,
clarification is enhanced by inclined plates that increase the settling area and efficiency
of particle removal. At the top of the clarification zone, clarified water is collected in sub-
merged orifice laterals or launders.
As solids are removed in the blanket and clarification zone, blanket volume increases
and some solids must be removed to maintain stable conditions. A zone of sludge con-
centrators collects and concentrates excess solids. As these excess solids increase the vol-
ume of the blanket, they spill over into the concentrators. When the concentrator is full,
thickened sludge is withdrawn through sludge removal headers usually on a timed basis
by automatically controlled sludge valves.

Design Criteria. Pulsed blanket clarifiers are sized based on surface loading rate in the
clarification zone. The area over the sludge concentrators is not included in this calcula-
tion. Typical design loading rates recommended by the manufacturer are as follows, but
lower rates may be required by some regulatory agencies and for some water quality con-
ditions (Webb, 1993):
Type of unit Loading rate
Pulsed blanket 1.0 to 1.25 gpm]ft 2 (2.4 to 3.1 m/h)
Pulsed blanket with plate settlers 2.0 to 4.0 gpm/ft 2 (4.9 to 9.8 m/h)
Pulsed blanket with plate and tube settlers 3.0 to 5.0 gpm/ft 2 (2.3 to 12.2 m/h)

Basin Dimensions. Basin dimensions are set to provide uniform flow distribution. A
typical Superpulsator consists of two 16-ft-wide (4.9-m) blanket sections with a cen-
tral 10-ft-wide (3-m) source water influent chamber, sludge concentrator, and effluent
section. Basin water depth is 16 ft (4.9 m). Basin length varies, limited by hydraulic
considerations.