55    THE USE OF A HIGH-RATE COMBINED
REACTOR/CLARIFIER/THICKENER
FOR THE TREATMENT OF INDUSTRIAL
WASTEWATERS
Marek K. Mierzejewski, Senior Engineer
Infilco Degremont Inc.
Richmond, Virginia 23229
Jean-Marie Rovel, Vice President
Degremont S.A.
Paris, France
Larry W. VandeVenter, Senior Process Consultant
H20 Inc.
Richmond, Virginia 23229
BACKGROUND
Over many years, the development of water treatment has been concerned primarily with the
removal of dissolved and suspended matter from the water and with the disposal of the material thus
removed. The concepts of clarification (and filtration) to achieve the first objective and sludge
thickening (prior to dewatering) for the second are well understood, yet still the subjects of considerable research and development. Whereas these objectives have been achieved and optimized using
several process units, there are clear advantages in combining such functions in one unit.
In 1966, a patent was issued which described the "high density process,"1 the essence of which lay in
the fact that under dynamic treatment conditions with defined solids recirculation modes and rates,
and specific solids concentrations and energy gradients, a denser sludge could be produced.
In the 1970s and 1980s, Degremont S.A. conducted research to optimize the blend of densification
and clarification technologies. In order to achieve the desired volumetric sludge reduction while
maintaining discharge quality standards and high rise rates, sludge densification processes were
combined with the application of lamellar settling technology as described by Hazen2 and Camp.3 The
result was development of the DensaDeg and a U.S. patent for this device was issued in 1986.4
DESCRIPTION
In its most complete version, the DensaDeg comprises three integrated modules: 1) a reactor; 2) a
presettler/thickener; and 3) a lamellar clarifier.
Figures 1 and 2 show the design principle and basic arrangement of the components.
REACTION MODULE
This comprises two co-axial cylinders. The inner is a draft tube equipped with one variable speed
axial flow impeller which can induce a recirculation 2-10 times that of the influent flow, which latter
is introduced at the base of this module. The outer annular space forms the recirculation zone. Two
zones thus exist where floe (or crystalline) growth takes place through internal sludge recirculation.
The solids concentration in this reaction module is maintained between 0.5 and 10 g/L, depending
on whether the treatment is flocculation or crystalline precipitation, by the introduction of concentrated sludge from the neighboring presettler/thickener into the raw water inlet (i.e., by external
sludge recirculation).
The module is sized on the basis of a Gt factor (velocity gradient x residence time) of the order of
50,000-100,000 with a residence time, based on the entire volume, of 8-10 minutes.
44th Purdue Industrial Waste Conference Proceedings, © 1990 Lewis Publishers, Inc., Chelsea, Michigan 48118.
Printed in U.S.A.
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