United States
Environmental Protection
                         Wastewater Technology Fact Sheet
                         Screening and Grit Removal
Wastewater contains large solids and grit that can
interfere with treatment processes or cause undue
mechanical wear and  increased maintenance on
wastewater treatment  equipment.   To  minimize
potential problems, these materials require separate
handling.  Preliminary treatment removes these
constituents   from  the  influent  wastewater.
Preliminary treatment  consists  of screening,  grit
removal, septage handling, odor control, and flow
equalization.  This fact sheet discusses  screening
and grit removal.


Screening  is the  first unit operation used at
wastewater treatment plants (WWTPs).  Screening
removes objects such as rags, paper, plastics, and
metals to  prevent  damage  and  clogging  of
downstream equipment, piping, and appurtenances.
Some modern wastewater treatment plants use both
coarse screens and fine screens.  Figure 1 depicts a
typical bar screen (a type of coarse screen).
  Source: Qasim, 1994.

                       Coarse Screens

                       Coarse screens remove large solids, rags, and debris
                       from wastewater, and typically have openings of 6
                       mm (0.25 in) or larger.  Types of coarse screens
                       include mechanically and manually  cleaned bar
                       screens, including trash racks. Table 1 describes the
                       various types of coarse screens.

                       Fine Screens

                       Fine screens are typically used to remove material
                       that may create operation and maintenance problems
                       in  downstream processes, particularly in systems
                       that lack primary treatment. Typical opening sizes
                       for fine screens  are 1.5 to 6 mm (0.06 to 0.25 in).
                       Very fine screens with openings of 0.2 to 1.5 mm
                       (0.01 to 0.06 in) placed after coarse or fine screens
                       can reduce  suspended solids to levels near those
                       achieved by primary clarification.

                       Comminutors and Grinders

                       Processing coarse solids reduces their size so they
                       can be  removed  during downstream  treatment
                       operations, such  as primary clarification, where both
                       floating   and  settleable  solids  are  removed.
                       Comminuting and grinding devices are installed in
                       the wastewater  flow channel to grind and shred
                       material up to 6  to 19 mm (0.25 to 0.75 in) in size.

                       Comminutors consist of a rotating slotted cylinder
                       through which wastewater flow passes. Solids that
                       are too large to  pass through the slots are cut by
                       blades as the  cylinder rotates,  reducing their size
                       until they pass through the slot openings.

                       Grinders  consist of two  sets of counterrotating,
                       intermeshing cutters that trap and shear wastewater
                       solids into a consistent particle size, typically 6 mm
                       (0.25 in).  The cutters are mounted on two drive


 Screen Type   Description

 Trash Rack      Designed to prevent logs, timbers,
                stumps, and other large debris from
                entering treatment processes.
                Opening size: 38 to 150 mm (1.5-6 in)

 Manually        Designed to remove large solids, rags,
 Cleaned Bar     and debris.
 Screen         Opening size: 30 to 50 mm (1 to 2 in)
                Bars set at 30 to 45 degrees from
                vertical to facilitate cleaning.
                Primarily used in older or smaller
                treatment facilities, or in bypass

 Mechanically     Designed to remove large solids, rags,
 Cleaned Bar     and debris.
 Screen         Opening size: 6 to 38 mm (0.25 to 1.5
                Bars set at 0 to 30 degrees from
                Almost always used in new
                installations because of large number
                of advantages relative to other
Source: Design of Municipal Wastewater Treatment Plants,
WEF MOP 8, Fourth Edition, 1998.

shafts with  intermediate  spacers.   The  shafts
counterrotate at different speeds to clean the cutters.
Figure 2 depicts a channel wastewater grinder.

The chopping action of the grinder reduces the
formation  of rag  "balls" and rag "ropes"  (an
inherent problem with comminutors). Wastewaters
that contain large quantities of rags and solids, such
as prison wastewaters, utilize grinders downstream
from coarse  screens  to  help  prevent frequent
jamming and excessive wear.

Grit Removal

Grit includes sand, gravel, cinder, or other heavy
solid materials that are "heavier" (higher specific
gravity) than the organic biodegradable solids in the
wastewater.  Grit  also includes eggshells, bone
chips, seeds,  coffee  grounds,  and large organic
particles,  such as food waste.  Removal of grit
prevents  unnecessary  abrasion  and   wear  of
mechanical equipment, grit deposition in pipelines
and channels, and accumulation of grit in anaerobic
digesters  and  aeration  basins.    Grit removal
facilities typically precede primary clarification, and
follow screening and comminution.  This prevents
large solids  from interfering with  grit handling
equipment.  In secondary treatment plants without
primary clarification, grit removal should precede
aeration(Metcalf&Eddy, 1991).

Many types of grit removal systems exist, including
aerated grit chambers, vortex-type (paddle or jet-
induced vortex) grit removal systems, detritus tanks
(short-term sedimentation basins), horizontal flow
grit  chambers (velocity-controlled   channel),  and
hydrocyclones  (cyclonic   inertial   separation).
Various factors must be taken into  consideration
when selecting a grit removal process, including the
quantity and characteristics of grit, potential adverse
effects  on   downstream  processes,  head  loss
requirements,  space   requirements,   removal
efficiency, organic content,  and cost. The type of
grit removal  system chosen for a specific facility
should be the one that best balances these different
considerations.  Specifics on the different types of
grit removal  systems are provided below.

Aerated Grit Chamber

In aerated grit chambers, grit is removed by causing
the wastewater to flow in a spiral pattern, as shown
  Source: WEF, 1998.

               CHANNEL UNIT

in Figure 3. Air is introduced in the grit chamber
along one side,  causing  a perpendicular spiral
velocity pattern to flow through the tank.  Heavier
particles are accelerated  and diverge from the
streamlines, dropping to the  bottom of the tank,
while lighter organic particles are suspended and
eventually carried out of the tank.
              Helical liquid
              flow pattern
         Outlet weir
  Trajectory ol
  grit particles
                                        - Air
                             Air ditfuser
Source: Crites and Tchobanoglous, 1998.


Vortex-Type Grit Chamber

The vortex-type  grit  chamber consists  of  a
cylindrical  tank  in  which  the  flow   enters
tangentially, creating a vortex flow pattern. Grit
settles by gravity into the bottom of the tank (in a
grit hopper) while effluent  exits at the top  of the
tank.  The grit that settles into the grit hopper may
be removed by a grit pump or an air lift pump.

Detritus Tank

A detritus tank (or square tank degritter) is  a
constant-level, short-detention settling tank.  These
tanks require a grit-washing step to remove organic
material. One  design option includes a grit auger
and a rake that removes and classifies grit from the
grit sump.

Horizontal Flow Grit Chamber

The horizontal flow grit chamber is the oldest type
of grit removal  system.    Grit is removed by
maintaining a constant up stream velocity of 0.3 m/s
(1 ft/s).   Velocity  is controlled by proportional
weirs  or  rectangular control sections, such  as
Parshall  flumes.   In  this  system,  heavier  grit
particles  settle to the bottom of the channel, while
lighter organic particles remain suspended or are
resuspended and transported out  of the  channel.
Grit is  removed  by  a conveyor with scrapers,
buckets,  or plows.   Screw  conveyors or bucket
elevators are used to elevate the grit for washing or
disposal. In smaller plants, grit chambers are often
cleaned manually.


Hydrocyclone systems are typically used to separate
grit from organics in grit slurries or to remove grit
from primary sludge. Hydrocyclones are sometimes
used to remove grit and suspended solids directly
from  waste water flow  by pumping  at   a head
ranging from 3.7 to 9 m (12 to 30  ft). Heavier grit
and  suspended solids collect on the sides  and
bottom of the  cyclone due to  induced centrifugal
forces, while scum and lighter solids are removed
from the  center through the top of the cyclone.


Because  various  types  of  screening  and  grit
removal  devices are available, it is important that
the proper  design be selected for each situation.
Though similarities exist between different types of
equipment  for a given process, an improperly
applied design may result in an inefficient treatment


As discussed  above,  most  large  facilities  use
mechanically cleaned screening systems to remove
larger materials because they reduce labor costs and
they improve flow conditions and screening capture.
Typically, only older or smaller treatment facilities
use a manually cleaned screen as the primary or
only screening device. A  screening compactor is
usually situated close to the mechanically cleaned
screen and compacted screenings are conveyed to a
dumpster or  disposal  area.   However,  plants
utilizing mechanically cleaned  screens should have
a  standby  screen to put  in operation when the
primary screening device is out of service. This is
standard  design practice for  most newly designed

The use of fine screens in preliminary treatment has
experienced a resurgence in the last 20 years. Such
screens were  a common feature before 1930 but
their  use  diminished because  of difficulty  in
cleaning oils and grease from the screens. In the
early  1980s,  fine screens  regained  popularity
because of improved materials.

Communitors and Grinders

Comminutors and grinders are used primarily at
smaller treatment facilities (less than 5 MOD) to
process material between 6 and 19 mm  (0.25 to
0.75 in) (WEF, 1998).  This shredded  material
remains in the wastewater  and is  removed in
downstream treatment processes.

Grit Removal

When selecting a grit removal process, the quantity
and characteristics of  grit and its  potential to
adversely   affect   downstream  processes   are
important  considerations.   Other  parameters to
consider may include headloss requirements, space
requirements, removal efficiency, organic content,
and economics.




Manually  cleaned  screens  require little or no
equipment  maintenance  and  provide  a  good
alternative for smaller plants  with few screenings.
Mechanically cleaned screens tend to have lower
labor costs than manually cleaned screens and offer
the advantages of improved  flow conditions  and
screening capture over manually cleaned screens.

Communitors and Grinders

A major advantage  of using  Communitors  and
grinders is that removal of grit reduces damage and
maintenance  to   downstream  processes.
Comminutors  and  grinders   also  eliminate
screenings  handling  and  disposal,  which  may
improve the aesthetics of the plant, reducing odors,
flies,   and  the  unsightliness   associated  with
screenings. Some recently developed grinders can
chop, remove, wash, and  compact the screenings.
The use of Comminutors in cold weather eliminates
the need  to  prevent  collected  screenings  from
freezing.  Comminutors and grinders typically have
a lower profile than screens, so cost savings can be
significant when the units must be enclosed.

Grit Removal

Aerated Grit Chamber

Some advantages of aerated grit chambers include:

•      Consistent removal efficiency over a wide
       flow range.

       A relatively low putrescible organic content
       may be removed with a well controlled rate
       of aeration.

•      Performance of downstream units may be
       improved by using pre-aeration to reduce
       septic conditions in incoming wastewater.

       Aerated  grit  chambers  are   versatile,
       allowing for chemical addition, mixing, pre-
       aeration, and flocculation.

Vortex-Type Grit Chamber

       These systems remove a high percentage of
       fine grit, up to 73 percent of 140-mesh (0.11
       mm/0.004 in diameter) size.

•      Vortex  grit  removal  systems  have  a
       consistent removal efficiency over a wide
       flow range.

       There are no submerged bearings or parts
       that require maintenance.

•      The "footprint" (horizontal dimension) of a
       vortex grit removal system is small relative
       to  other grit removal systems, making  it
       advantageous when space is an issue.

       Headloss  through a  vortex  system   is
       minimal, typically 6 mm (0.25 in).  These
       systems are also energy efficient.

Detritus Tank
Grit Removal
Detritus tanks do not require flow control because
all bearings and moving mechanical parts are above
the water line.  There is minimal headloss in this
type of unit.

Horizontal Flow Grit Chamber

Horizontal flow grit chambers are flexible because
they allow performance to be  altered by adjusting
the outlet flow control device. Construction is not
complicated.   Grit  that  does  not require further
classification may be removed with effective flow


Hydrocyclones can remove both grit and suspended
solids  from  wastewater.  A  hydrocyclone  can
potentially  remove  as many  solids as a primary



Manually cleaned screens require frequent raking to
avoid clogging and high backwater levels that cause
buildup  of a solids mat on the  screen.   The
increased raking frequency increases labor costs.
Removal of this mat during cleaning may also cause
flow surges  that  can reduce the  solids-capture
efficiency of downstream  units.   Mechanically
cleaned screens are not subject to this problem, but
they have high equipment maintenance costs.

Communitors and  Grinders

Comminutors and grinders can create problems for
downstream processes, such as increasing plastics
buildup in digestion tanks or rag accumulation on
air diffusers.  In addition, solids from comminutors
and grinders will  not  decompose  during the
digestion process. If these synthetic solids are not
removed, they may  cause biosolids to be rejected
for reuse as a soil amendment.
Grit removal systems increase the headloss through
a wastewater treatment  plant, which could be
problematic if headloss is  an  issue.   This could
require additional pumping to compensate for the

The following  paragraphs describe  the  specific
disadvantages of different  types of grit removal

Aerated Grit Chamber

Potentially harmful volatile organics and odors may
be released from the aerated grit chamber. Aerated
grit chambers also require more power than other
grit removal processes, and maintenance and control
of the aeration system requires additional labor.

Vortex-Type Grit Chamber

•      Vortex grit removal systems are usually of a
       proprietary   design,   which   makes
       modifications difficult.

•      Paddles tend to collect rags.

•      Vortex units usually require deep excavation
       due to their depth, increasing  construction
       costs,  especially  if unrippable  rock is

       The grit  sump tends to clog and  requires
       high-pressure agitation using water or air to
       loosen grit compacted in the sump.

Detritus Tank

•      Detritus  tanks  have difficulty achieving
       uniform flow distribution over a wide range
       of flows because the inlet baffles cannot be

•      This type of removal system removes large
       quantities of organic material,  especially at
       low flows,  and  thus requires grit washing
       and classifying.

•      Grit may be lost in shallow installations
       (less than 0.9 m [3 ft]) due to the agitation
       created by the rake arm associated with this

Horizontal Flow Grit Chamber

       It is difficult to maintain a 0.3 m/s (1 ft/s)
       velocity over a wide range of flows.

•      The submerged chain, flight equipment, and
       bearings undergo excessive wear.

•      Channels without effective flow control will
       remove  excessive  amounts  of  organic
       material  that require grit  washing and

•      Head loss is excessive (typically 30 to 40
       percent of flow depth).

       High  velocities  may  be generated at the
       channel bottom with the use of proportional
       weirs, leading to bottom scour.


Hydrocyclones require energy because they use a
pump to remove grit and suspended solids. Coarse
screening is required before these units to remove
sticks, rags, and plastics.



Screening devices are classified based on the size of
the  material they  remove (the screenings). The
"size" of screening material refers to its diameter.
Table 2 lists the correlation between screening sizes
and screening device classification.

In  addition  to  screening  size,  other  design
considerations  include the  depth,  width,  and
approach  velocity of the  channel; the  discharge
height, the  screen  angle; wind  and  aesthetic
considerations; redundancy; and head loss.

Table 3 lists typical design criteria for mechanically
cleaned bar rack type screens.

 Screening Device      Size Classification/Size
 Classification        Range of Screen Opening
 Bar screen
 Manually Cleaned       Coarse/25-50 mm
                      (1-2 in)
 Mechanically Cleaned   Coarse/15-75 mm
                      (0.6-3.0 in)
 Fine bar or perforated coarse screen (mechanically
 Fine Bar
 Perforated Plate
 Rotary Drum
Fine Coarse/3-12.5 mm
(0.1-0.5 in)

Fine Coarse/3-9.5 mm
(0.1-0.4 in)

Fine Coarse/3-12.5 mm
(0.1-0.5 in)
 Fine screen (mechanically cleaned)
 Fixed Parabolic

 Rotary Drum

 Rotary Disk
Fine/0.25-3.2 mm
(0.01-0.13 in)

Fine/0.25-3.2 mm
(0.01-0.13 in)

Very fine (micro)/0.15-0.38 mm
(0.01-0.02 in)  	
 Source: Crites and Tchobanoglous, 1998.

The  use  of  fine  screens  produces  removal
characteristics similar to primary sludge removal in
primary sedimentation. Fine screens are capable of
removing 20 to 35 percent suspended solids and
BOD5.   Fine  screens  may be either  fixed or
movable, but are  permanently  set in a vertical,
inclined, or horizontal position and must be cleaned
by rakes, teeth, or brushes.

Communitors and Grinders

Figure 4 depicts  a typical  comminutor. When
designing  a  comminutor,  headloss  should  be
considered.   Headloss through  a comminutor is
usually in the range of a few centimeters to 0.9 m (3
ft).  Therefore, the manufacturer's ratings should be
decreased by 70  to  80 percent to  account  for
clogging  of  the  screen,  since  manufacturer's
headloss characteristics are usually based on clean
water flow (Crites  and Tchobanoglous, 1998).

                       Design Criteria
                 Metric Units    English Units
Bar width
Bar depth
Clear spacing
between bars
Slope from
5-15 mm
25-40 mm
15-75 mm
0-30 degrees
0.6-1.0 m/s
150 mm
0.2-0.6 in
1.0-1. 5 in
0.6-3.0 in
0-30 degrees
2.0-3.25 ft/s
6 in
Source: WEF, 1998.
When a comminution device is installed upstream
of  a  grit  removal  device, the  teeth  of  the
comminutor are  subject to high wear and tear.
Rock traps are recommended to prolong the life of
the comminutor. In addition, a bypass manual  bar
rack should be installed in the event that flow rates
exceed the comminutor capacity  or there is a
mechanical failure.
Grit Removal

With respect  to  grit removal  systems,  grit is
traditionally defined as particles larger than 0.21
mm (0.008 in) (65 mesh) and with a specific gravity
of greater than 2.65 (U.S. EPA, 1987). Equipment
design was traditionally  based on removal of 95
percent of these particles. However, with the recent
recognition that smaller particles must be removed
to avoid damaging downstream processes, many
modern  grit removal  designs  are capable  of
removing up to 75 percent of 0.15 mm (0.006 in)
(100 mesh) material.

Aerated Grit Chamber

Aerated grit chambers are typically designed to
remove particles of 70 mesh (0.21 mm/0.008 in) or
larger, with a  detention period  of two  to five
minutes at peak hourly flow. When wastewater
flows into the grit chamber, particles settle to the
bottom according to their size, specific gravity, and
the velocity of roll  in the tank. A velocity that is too
high will result in lower  grit removal efficiencies,
while  a  velocity  that is too low will  result in
increased removal of organic materials.   Proper
adjustment of air velocity will result in nearly 100
percent removal of the desired particle size and a
well-washed grit.

Design considerations for aerated grit chambers
include the following (WEF 1998):
                                                     Motor and Gear Drive
Source: Reynolds/Richards, 1996.


•      Air rates typically range  from 0.3 to 0.7
       m3/m»min (3 to 8 ftVftrmin) of tank length.

•      A typical  minimum  hydraulic  detention
       time at maximum instantaneous flow is two

       Typi cal 1 ength-to-wi dth rati o i s 2.5:1 to 5:1.

       Tank inlet and outlet are positioned so the
       flow is perpendicular to  the  spiral roll

       Baffles are  used to  dissipate  energy and
       minimize short circuiting.

Vortex-Type Grit Chamber

Two designs of vortex grit units  exist: chambers
with flat bottoms and  a small opening to collect
grit; and chambers with a sloping bottom and  a
large  opening into  the  grit hopper.  Flow into  a
vortex-type grit system should be straight,  smooth,
and streamlined. The straight inlet channel length
is typically seven  times  the width of the  inlet
channel, or 4.6 m (15 ft), whichever is greater. The
ideal velocity range in the influent is typically 0.6 to
0.9 m/s (2 to  3 ft/s) at 40 to 80  percent  of peak
flow.  A minimum velocity of 0.15 m/s (0.5 ft/s)
should be maintained at all times, because lower
velocities will not  carry grit into the grit  chamber
(WEF, 1998).

Detritus Tank
of the target grit  particles  and the flow control
section-depth relationship.  An allowance for inlet
and outlet turbulence is added. The cross sectional
area of the channel is determined by the rate of flow
and the number of channels. Allowances are made
for grit storage and grit removal equipment.  Table
4  lists  design  criteria for horizontal  flow  grit
                         Design Criteria
                    Range Metric
 Detention time

 Horizontal velocity

 Settling velocity1:



 Headless (% of
 channel depth)

 Inlet and outlet
 length allowance
  45-90 s

0.24-0.4 m/s
(0.8-1.3 ft/s)

0.3 m/s
(1.0 ft/s)
2.8-3.1 m/min
(9.2-1 0.2 ft/min)
0.6-0.9 m/min
(2.0-3.0 ft/min)
2.9 m/min
(9.6 ft/min)
0.8 m/min
(2. 5 ft/min)
 11f the specific gravity of the grit is significantly less than 2.65,
 lower velocities should be used.
 2For Parshall flume control.

 Source: Crites and Tchobanoglous, 1998.
Detritus  tanks are designed to  keep horizontal
velocity  and  turbulence at a  minimum while
maintaining a detention  time  of less than one
minute. Proper operation of a detritus tank depends
on well-distributed flow into the settling basin.
Allowances are made for inlet and outlet turbulence
as well as short circuiting  by  applying a safety
factor of 2.0 to the calculated overflow rate.

Horizontal Flow Grit Chamber

Horizontal flow  grit  chambers  use proportional
weirs or rectangular control sections to vary the
depth of flow and keep the velocity  of the flow
stream at a constant 0.3  m/s (1 ft/s). The length of
the grit chamber is governed by the settling velocity

The use of screening and grit removal systems is
well documented.  The performance of bar screens
varies depending on the spacing of the bars.  Table
5 lists typical screening quantities for various screen

The quantity of screenings depends on the length
and slope of the collection system and the presence
of pumping stations.  When the collection system is
long and steep  or when  pumping  stations  exist,
fewer  screenings   are   produced  because   of
disintegration of solids.  Other factors that  affect
screening quantities are related to flow, as quantities
generally increase greatly during storm flows. Peak

   Screen Size
  Screenings Quantity

m3/106m3       ft3/Mgal
13 mm (0.5 in)
38 mm (1.5 in)
 Source: Reynolds and Richards, 1996.

daily removals  may vary by a 20:1 ratio on  an
hourly   basis  from  average  flow  conditions.
Combined collection systems may produce several
times the coarse screenings produced by  separate
collection systems.

Given the complexity of collection  systems and
types of materials that may be considered "grit," the
quantity and characteristics of grit removed from
wastewater will vary. Grit quantity is influenced by
the type and condition of the collection system, the
characteristics  of the  drainage  area,   garbage
disposal  methods, the slope of  the  collection
system,  and the efficiency of the grit  removal
system.  The quantity of grit may vary from 0.004
to 0.21 m3/103m3 (0.5 to 30 ft3/Mgal) (Crites and
Tchobanoglous, 1998).  The performance of a grit
removal system may be enhanced if actual plant
data is used when designing a new  grit  removal
Table 6 depicts quantities of screenings and grit
from various wastewater treatment plants.  There
are no obvious trends associated with design flow
through a plant and grit and screenings removal
quantities. Differences in wastewater characteristics
and  equipment efficiencies  make  a correlation
between flow and quantities of screenings and grit
removed nearly impossible.



Manually cleaned screens require frequent raking to
prevent clogging.  Cleaning frequency depends on
the characteristics  of the wastewater entering a
plant.  Some plants have incorporated  screening
devices, such as basket-type trash racks, that are
manually  hoisted  and cleaned.   Mechanically
cleaned screens usually  require less labor for
operation than manually cleaned screens because
screenings  are raked with  a mechanical device
rather than by facility personnel.  However, the rake
teeth on mechanically  cleaned  screens must be
routinely inspected because of their susceptibility to
breakage and bending. Drive mechanisms must also
be frequently inspected to prevent fouling due to grit
and rags.   Grit removed from  screens must be
disposed of regularly.
Plant Location
Uniontown, Pennsylvania
East Hartford, Connecticut
Duluth, Minnesota
Lamberts Point Water Pollution Control Plant,
Norfolk, Virginia
Village Creek Wastewater Treatment Plant,
Ft. Worth, Texas
County of Milwaukee, Wisconsin, South Shore
Twin Cities Metro Wastewater Treatment Plant,
Chicago, Illinois (Northside)
Flow, m3/d
75,700 (20.0)
Grit, m3/103m3
0.034 (4.85)
0.003 (0.48)
0.034 (4.82)
0.004 (0.56)
0.005 (0.72)
0.004 (0.60)
0.006 (0.83)
aft3/Mgal=cubic feet per million gallons
Source: WEF, 1998.

Communitors and Grinders

Comminutors can create operation and maintenance
problems  in  downstream  processes.    While
shredding solids eliminates the problem of handling
screening  materials at the head of the plant,
problems inherent to the use of communitors,  such
as the decreased quality of digested biosolids and
the accumulation  of rags on  air diffusers,  have
lessened  the  popularity  of  this  technology.
Comminutors are generally avoided in new designs
and are being removed from many existing plants.
Grinders  are greatly affected by grit and other
solids.  As such, they require routine inspection
every six months and replacement of bearings and
cutter teeth every one to three years.

Grit Removal
equipment, and applicability of various technologies
to different situations.

Graphs can be used to relate average wastewater
flow through a  plant to a specific technology.
Figure 5 shows a graph relating wastewater flow to
the cost of a horizontal shaft rotary screen.  Costs
include construction, operation, and maintenance.
Contractor bids  on a recent wastewater project
ranged from $150,000 to $400,000 for Rotary Drum
Screenings  Removal  and  from  $150,000  to
$208,800   for   Vortex-type   Grit  Removals.
Generally, equipment costs will be close for each
bid.  However,  the overall costs vary for each
treatment process/project because of differences in
construction approaches by the contractors.

Collected grit must be removed from the chamber,
dewatered, washed, and conveyed to a disposal site.
Some smaller pi ants use manual methods to remove
grit, but grit removal is usually accomplished by an
automatic method. The four methods of automatic
grit removal  include  inclined screw or tubular
conveyors, chain and bucket elevators, clamshell
buckets, and pumping. A two-step grit removal
method is sometimes used, where grit is conveyed
horizontally in a trough or channel to a hopper,
where it is then elevated from the hopper to another

Aerated grit chambers use a sloped tank bottom in
which the air roll pattern sweeps grit along the
bottom to  the  low side of the  chamber.   A
horizontal  screw  conveyor  is typically used to
convey settled grit to a hopper at the head of the
tank.   Another method to remove grit from the
chamber floor is a chain and flight mechanism.

Once  removed from the chamber, grit is usually
washed with a hydrocy clone or grit classifier to ease
handling and remove organic material. The grit is
then  conveyed directly to a truck,  dumpster, or
storage hopper. From there, the grit is taken to a
landfill or other disposal facility.


The cost of screens and grit removal systems varies
depending on the type of technology used, ancillary
Other Related Fact Sheets
               Wastewater Flow MGD
             •Construction Cost •
  Source: Martin, 1991.

Sewer Lift Station
EPA 832-F-00-073
September 2000

Sewer Cleaning & Inspection
September 1999

EPA 832-F-99-040
September 1999

Other EPA  Fact  Sheets  can be  found at the
following web address:

1.      C rites, R.  and  G.  Tchobanoglous,  1998.
       Small and  Decentralized  Wastewater
      Management Systems. The McGraw-Hill
       Companies. Boston, Massachusetts.

2.      Martin,  E.J.  and  E.T.  Martin,  1991.
       Technologies  for  Small  Water  and
       Wastewater  Systems.    Van  Nostrand
       Reinhold. New York, New York.

3.      Qasim, S., 1994.  Wastewater Treatment
      Plants: Planning, Design and Operation.
       Technomic  Publishing  Co.,  Lancaster,

4.      Reynolds, T. and P. Richards, 1996.  Unit
       Operations and Processes in Environmental
      Engineering.  PWS  Publishing Company.
       Boston, Massachusetts.

5.      Urquhart, L.,  1962.  Civil Engineering.
       Costs include construction,  operation, and
       maintenance.   Specific cost data  from
       contractor bids.

6.      Water Environment  Federation,  1998.
      Design ofMunicipal Wastewater Treatment
      Plants.   Water  Environment Federation.
       Alexandria, Virginia.


H.I.L. Technology, Inc.
94 Hutchins Drive
Portland, ME 04102
Lakeside Equipment Corporation
1022 E. Devon Ave.
Bartlett, IL60103

National Small Flows Clearing House
at West Virginia University
P.O. Box 6064
Morgantown, WV 26506

Parkson Corporation
2727 NW 62nd Street
P.O. Box 408399
Fort Lauderdale, FL 33340-8399

U.S. Filter
Link-Belt Headworks Products
100 High Point Drive - Suite 101
Chalfont, PA 18914
The mention of trade names or commercial products
does not constitute endorsement or recommendation
for use by  the  U.S.  Environmental Protection
Agency (EPA).

               Office of Water
                  June 2003

       For more information contact:

       Municipal Technology Branch
       U.S. EPA
       Mail Code 4204
        1200 Pennsylvania Avenue, NW
       Washington, D.C. 20460
                                                         Excellence in compliance through optimal technical solutions
                                                         MUNICIPAL TECHNOLOGY BRAN^fff