United States
Environmental Protection
Agency
DESCRIPTION
Ballasted flocculation, also known as high rate
clarification, is a physical-chemical treatment
process that uses continuously recycled media and
a variety of additives to improve the settling
properties of suspended solids through improved
floe bridging. The objective of this process is to
form microfloc particles with a specific gravity of
greater than two. Faster floe formation and
decreased particle settling time allow clarification
to occur up to ten times faster than with
conventional clarification, allowing treatment of
flows at a significantly higher rate than allowed by
traditional unit processes.
Ballasted flocculation units function through the
addition of a coagulant, such as ferric sulfate; an
anionic polymer; and a ballast material such as
microsand, a microcarrier, or chemically enhanced
Wastewater Technology Fact Sheet
Ballasted Flocculation
sludge. When coupled with chemical addition, this
ballast material has been shown to be effective in
reducing coagulation-sedimentation time (Liao, et
al., 1999). For instance, ballasted flocculation units
have operated with overflow rates of 815 to 3,260
L/m2-min (20 to 80 gal/ft2-min) while achieving
total suspended solids removal of 80 to 95 percent
(Tarallo, et al., 1998).
The compact size of ballasted flocculation units
makes them particularly attractive for retrofit and
high rate applications. This technology has been
applied both within traditional treatment trains and
as overflow treatment for peak wet weather flows.
Several different ballasted flocculation systems are
discussed in more detail below:
The Actiflo® process (Figure 1), manufactured by
US Filter Kruger (US operations) has been used in
Sludge Handling
-4
Coagulant
Hydrocyclone
4
Microsand and Sludge to Hydrocyclone
Influent Water from
Grit Chamber
Inclined Plate Settler with
Scraper
Source: Modified from US Filter Kruger, 2002.
FIGURE 1 ACTIFLO® PROCESS DIAGRAM
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Europe since 1991 for drinking water, wastewater,
and wet weather applications. This three-stage
process uses microsand particles (45-100 ^m in
diameter) to enhance the flocculation process.
Prior to entering the first stage of the Actiflo®
process, the influent wastewater is usually screened
and passed through a grit chamber to remove large
particulates. The next step is the addition of a
traditional metal coagulant in a flash mixer. Iron or
aluminum coagulants are used to reduce
phosphorus levels, typically to below 2 mg/L.
Within this first stage, a polymer and microsand
(the ballast materials) are also added.
The second stage of the Actiflo® process is
maturation, where the ballast material serves to
enhance floe formation, resulting in a much faster
settling rate relative to traditional coagulants. The
influent wastewater then flows to a second tank
where it is gently mixed with chemical flocculants
and ballast to enhance the flocculation process.
The third stage of the Actiflo® process is
clarification. During this stage, the mixed influent
and the floe flow downward through the unit. The
floe settle by gravity to the bottom of the unit where
they are collected, typically in a cone-shaped
chamber. A baffle is used to direct the flow to the
top of the tank for further settling. Inclined tube
settlers further enhance the settling process by
providing a greater surface area over which settling
can occur and by reducing settling depth. Clarified
effluent is then directed to the next process
treatment or to discharge. Ballast from the bottom
of the chamber is separated from the sludge and re-
introduced into the contact chamber. A
hydrocyclone uses centrifugal force to separate the
sludge from the ballast and re-introduces it into the
contact chamber. The sludge is taken to an
appropriate handling facility.
Marketed by Infilco Degremont, Inc., of Richmond,
Virginia, and first installed in 1984, the
DensaDeg® process, shown in Figure 2, is a high-
rate clarifier designed for grit removal, grease
removal, settling, and thickening. The DensaDeg®
reuses recirculated sludge in combination with a
flocculating agent to achieve rapid settling. Like
the Actiflo® system, the first step in the
DensaDeg® process involves the injection of a
traditional coagulant into the system. However,
unlike the Actiflo® system, the DensaDeg® process
uses inj ected air rather than flash mixing to disperse
the coagulant. The DensaDeg® 4D uses the same
technology and processes as the DensaDeg® but can
handle flows with the rapid start-up and shut-down
time frame typically required for stormwater,
combined sewer overflow (CSO), and sanitary
sewer overflow (SSO) applications.
In the coagulation zone of the DensaDeg®, air is
Coagulating
Agent
Grease and Scum
Drawoff
Influent
Water
Clarified
Water
Grit Drawoff
Sludge Densification
and Thickening
Sludge Handling
Source: Modified from ONDEO-Degremont, Inc., 2002.
FIGURE 2 DENSADEG 4D PROCESS DIAGRAM
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simultaneously injected with the coagulant to
separate grit particles from organic matter and to
provide fluid motion for coagulant dispersion and
mixing. Coagulated wastewater enters the reactor
where a polymer flocculating agent is added with
recycled settled sludge to help the flocculation
process. In the reaction zone, wastewater enters a
clarifer where grease and scum are drawn off the
top. In the final step of the process, inclined tube
settling is used to remove residual floe particles.
Settled sludge from the clarifier is thickened, and
part of this sludge is recirculated and added to the
flocculate. Because this system uses entirely
recycled sludge as a coagulant aid, it does not
require separation techniques (hydrocyclone) to
recover microsand from the sludge.
The Lamella® plate clarification system, which is
manufactured by the Parkson Corporation of Ft.
Lauderdale, Florida, is usually used in conjunction
with non-proprietary coagulation and flocculation
units rather than as a single flocculation and
clarification process. The Lamella® system does
not include a microcarrier, but enhanced
coagulation aids (ballast materials) can be used with
this system to achieve enhanced high-rate
clarification. This system uses a series of inclined
plates to increase the surface area over which
particles can settle out. Because the plates are
stacked at an incline, the depth from which they
must settle is significantly less than those of
traditional clarifiers. This decreases settling time
compared to that of traditional clarifiers, allowing
much higher flow rates to be treated. A thickener
can be added to the Lamella® unit to increase the
concentration of solids in the resulting sludge. Like
the DensaDeg® system, underflow sludge can be
routed back to the flocculation unit for use as a
ballast material.
Like other ballasted processes, the Lamella®
system can be used in either new designs or
retrofits to achieve high rate clarification. The
advantages of other systems incorporating the use
of a microcarrier are also applicable to the Lamella®
system. Figure 3 shows atypical Lamella® system.
APPLICABILITY
Ballasted flocculation can be used as part of a
traditional treatment train or as a parallel treatment
train in new or existing wastewater facilities.
Applications of ballasted flocculation include:
1. Enhanced primary clarification.
2. Enhanced secondary clarification following
fixed and suspended growth media
biological processes.
3. Peak flow reduction for CSO and SSO
treatment. This process has been applied to
a variety of wastewater facilities ranging
from less than 0.1 MOD to more than 1,000
MGD, both as a parallel train and as a
means of optimizing existing unit processes
(Infilco Degremont, 2000).
ADVANTAGES AND DISADVANTAGES
Advantages
Major advantages for both new and upgraded
treatment operations include:
The reduced surface area of the clarifiers
minimizes short-circuiting and flow patterns
caused by wind and freezing (a problem
only in extremely cold climates).
• Systems using ballasted flocculation can
treat a wider range of flows without
reducing removal efficiencies.
• Ballasted flocculation systems reduce the
amount of coagulant used, or improve
settling vs. traditional systems for
comparable chemical usage.
In CSO and SSO applications:
Ballasted flocculation requires less land
than a storage tank of comparable capacity.
The compact size of the clarifier can
significantly reduce land acquisition and
construction costs.
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Thickener/Scraper Drive
Optional: Flocculation Units
Effluent
Plate
Packs
Optional:
Picket-Fence
Thickener
Scrapers
Underflow
~~sTudge~~~
Source: Parsons, Inc., from Parkson Corporation, 2000.
FIGURE 3 LAMELLA® PLATE SETTLERS
Operational costs are incurred only during
use.
• These systems do not require conveyance of
flow to wastewater treatment plants
following wet-weather events (if secondary
treatment requirements do not apply).
Ballasted flocculation systems can be used
as primary treatment facilities for primary
rehabilitation or replacement projects.
Disadvantages
Some disadvantages of ballasted flocculation
systems include:
• They require more operator judgment and
more complex instrumentation and controls
than traditional processes.
• Pumps may be adversely affected by ballast
material recycle. Lost microsand or
microcarrier must be occasionally replaced
(except where settled sludge is recycled for
use as a microcarrier/ballast).
For CSO and SSO applications:
Systems require significantly more
operation and chemical feed than a
comparable storage tank of similar capacity.
Use of ballasted flocculation systems results
in low removal rates during the start-up
period (typically 15 to 20 minutes after a
wet weather event).
• The process may take several hours to
achieve the optimal chemical dose and
hence, the desired pollutant removal.
• This is a relatively new technology for
CSO/SSO abatement without a history of
long-term performance.
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DESIGN CRITERIA
(Parkson, 2000).
The Actiflo® can process flows between 10 and 100
percent of its nominal design capacity, allowing
systems to provide wet weather treatment for a
range of design storm events. Typical start-up to
steady-state time is about 30 minutes. Table 1
shows additional design parameters for the Actiflo®
system.
The DensaDeg® unit has been successfully applied
to treat hydraulic loads of 20 to 40 m3/m2-h (11,800
to 23,600 gal/ft2-d). Start-up to steady state times
range from 15 to 30 minutes. Within the grit
removal coagulation reactor, a high solids
concentration (>500 mg/L) is maintained. Settling
rates within the clarifier are as high as 2,450
L/m2-min. (60 gal/ft2-min.). The solids removed
from the clarifier/thickener are typically 3 to 8
percent dry solids. Additional thickening is not
required in most cases. Table 1 provides additional
design parameters for the DensaDeg®.
Loading rates used in conventional settlers can
typically be applied directly to sizing Lamella®
settlers by substituting the projected area for the
surface provided by a conventional clarifier
(Parkson, 2000). The surface area depends upon the
angle of plate inclination, with typical applications
at about 55 degrees. Lamella® plate packs are
proportioned to the clarification and thickening area
by adjusting the plate feed point.
The ratio of clarification to the thickening area is
determined from representative wastewater samples
PERFORMANCE
Pilot studies were conducted for both the Actiflo®
and DensaDeg® 4D processes to evaluate their
pollutant removal abilities.
The Actiflo® process was evaluated at the Airport
Wastewater Treatment Plant in Galveston, Texas,
under both wastewater and CSO simulated
conditions. Table 2 summarizes removal rates for
both influent conditions.
The DensaDeg® 4D process was evaluated by the
Village Creek WWTP in Birmingham, Alabama, as
a method of treating peak flows. Pilot studies were
conducted to determine optimum operating
parameters. During testing, primary effluent was
selected to best represent SSO influent (with the
assumption that a surge tank with a detention time
of two hours would collect SSO volume before
being discharged to the DensaDeg® for treatment).
Table 3 lists removal efficiencies achieved under
optimum steady-state operating parameters.
The city of Fort Worth, Texas, conducted pilot
tests of several ballasted flocculation treatment
processes during the design of a new treatment
facility for peak flow treatment. Results indicated
that every tested process achieved a higher degree
of pollutant removal when compared to
conventional preliminary treatment. Table 4
shows the removal efficiencies of different
TABLE 1 DESIGN PARAMETERS FOR BALLASTED FLOCCULATION SYSTEMS
Parameter
Microsand (percent of peak raw
water flow) or Ballasted Sludge
Overflow Rate
Reactor Retention Time
Total Retention Time
Minimum Single Train Capacity
Maximum Multiple Train Capacity
Maximum Single Train Capacity
Actiflo®
45-150 nm
2,450 L/m2-min.
3-5 minutes
4-7 minutes
0.2 MGD
Unlimited
90 MGD
DensaDeg®
0.5-4.0%
up to 450 L/m2-min.
6 minutes
22 minutes
0.8 MGD
Unlimited
24 MGD
DensaDeg® 4D
0.5-4.0%
up to2,040 L/m2-min.
4-6 minutes
15 minutes
8 MGD
Unlimited
100 MGD
Source: US Filter, 2000 and Infilco Degremont, 2000.
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TABLE 2 PERFORMANCE OF ACTIFLO® PROCESS AT GALVESTON, TEXAS
TSS Removal
COD % Removal
BOD % Removal
Raw Wastewater
CSO Simulated
71-95%
80-94%
66-87%
65-83%
55-88%
48-75%
Source: US Filter Kruger, 2000.
treatment technologies during this pilot study.
OPERATION AND MAINTENANCE
In general, proper operation of a ballasted
coagulation and flocculation system requires greater
operator expertise than does operation of
conventional coagulant systems because the
addition of ballast requires close monitoring of the
recycle. The short retention time also requires
prompt operator response to maintain design
conditions and to provide optimum coagulant
dosages.
For wet weather applications, maintenance
requirements for ballasted flocculation units are
greater than for traditional storage tanks, which
retain wet weather volume for subsequent treatment.
Wet weather suspended solids concentrations vary,
and require monitoring and adjustment of the
microsand concentration and overflow rate. As with
non-wet weather applications, the polymer dose,
coagulant doses, and pH of coagulation should be
closely monitored to ensure design conditions are
met.
Most systems recover and recycle the ballast
material using a hydrocyclone. It is important to
ensure proper operation and maintenance of the
TABLE 3 REMOVAL EFFICIENCIES OF
THE DENSADEG® 4D PROCESS AT
BIRMINGHAM, AL WWTP
Parameter
COD
TSS
Influent
Range
(mg/L)
112-260
47-86
Effluent
Range
(mg/L)
44-168
3-11
Removal
Efficiency
45-60%
80-95%
Source: Tarallo, etal., 1998.
hydrocyclone to avoid accumulation of organic
material on the sand particles. This does not occur
in systems that use only sludge recycle.
COSTS
The compact design of ballasted flocculation units
reduces land acquisition costs when compared to
conventional treatment trains, reducing capital
costs, especially where land acquisition is
expensive or prohibitive. However, operational
costs can be higher than for comparable
conventional processes. For wet weather
applications, operational costs are incurred only
during peak flow conditions. Capital and
operating costs vary depending on the specific
treatment application. In Fort Worth, Texas,
capital costs for ballasted flocculation were
$0.05/L treated ($0.20/gal) with operating costs of
$24/million L treated ($90.85/million gal) (Camp,
Dresser & McKee, 1999).
REFERENCES
Other Related Fact Sheets
Chemical Precipitation
EPA832-F-00-018
September 2000
Other EPA Fact Sheets can be found at the
following web address:
http://www.epa. gov/owm/mtb/mtb fact, htm
1. Camp, Dresser & McKee, Inc., 1999. High
Rate Clarification Saves Fort Worth $34
Million. Internet site at
http://www.cdm.com/Svcs/
wastewtr/balfloc.htm, accessed 2000.
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TABLE 4 REMOVAL EFFICIENCIES OF TREATMENT TECHNOLOGIES AS PILOT
TESTED FOR THE CITY OF FORT WORTH, TEXAS
Unit/Manufacturer
Actiflo®
DensaDeg®
Lamella®
BOD Removal
36-62%
37-63%
41-57%
TSS Removal
74-92%
81-90%
53-73%
TKN Removal
25-30%
28-40%
19-34%
Phosphorus Removal
92-96%
88-95%
69-76%
Source: Crumb and West, 2000.
Note: A fourth system, Microsep®, was evaluated but is no longer manufactured.
2. Crumb, F.S. and R. West, 2000. After the
Rain, Water Environment and Technology,
April 2000.
3. Infilco Degremont, 2000. Design
information on the DensaDeg system.
4. Liao, S.-L., Y. Ding, C.-Y. Fan, R. Field,
P.C. Chan, and R. Dresnack, 1999. High
Rate Microcarrier-Weighted Coagulation
for Treating Wet Weather Flow. Water
Environment and Technology Poster
Symposium, New Orleans, LA.
5. Parkson Corporation, 2000. Principle of
Lamella Gravity Settler.
6. Tarallo, S., M. W. Bowen, A. J. Riddick,
and S. Sathyamoorthy, 1998. High Rate
Treatment ofCSO/SSO Flows Using a High
Density Solids Contact Clarifier/Thickener-
Results from a Pilot Study.
7. US Filter Kruger, 2000. Design information
on the Actiflo® process for wastewater.
ADDITIONAL INFORMATION
US Filter Kruger, Inc.
Mike Gutshall
401 Harrison Oaks Boulevard, Suite 100
Cary,NC27513
Infilco Degremont, Inc.
Steve Tarallo
P.O. Box 71390
Richmond, VA 23255-1390
Parkson Corporation
2727 NW 62nd Street
P.O. Box 408399
Fort Lauderdale, FL 33340-8399
Camp, Dresser & McKee
Randel L. West, P.E.
8140 Walnut Hill Lane, Suite 1000
Dallas, TX 75231
The mention of trade names or commercial
products does not constitute endorsement or
recommendation for use by the U. S. Environmental
Protection Agency.
Office of Water
EPA 832-F-03-010
June 2003
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For more information contact:
Municipal Technology Branch
U.S. EPA
ICC Building
1200 Pennsylvania Ave., NW
7th Floor, Mail Code 4204M
Washington, D.C. 20460
* 2002 +
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CIJ-AN WATER
IMTB
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