United States
                       Environmental Protection
                       Office of Water
                       Washington, D.C.
September 2000
Waste water
Technology  Fact  Sheet
Package  Plants

Package plants are pre-manufactured treatment
facilities used  to treat  wastewater  in  small
communities  or  on   individual   properties.
According to manufacturers, package plants can be
designed to treat flows as low as 0.002 MGD or as
high as 0.5 MGD, although they more commonly
treat flows between 0.01 and 0.25 MGD (Metcalf
and Eddy, 1991).

The most common types of  package plants are
extended aeration plants, sequencing batch reactors,
oxidation ditches, contact stabilization plants,
rotating   biological   contactors,   and
physical/chemical  processes (Metcalf and  Eddy,
1991).  This fact sheet focuses  on the first three, all
of which are biological aeration processes.

Extended aeration plants

The extended aeration process is one modification
of the  activated  sludge process which  provides
biological   treatment  for  the   removal  of
biodegradable  organic   wastes  under  aerobic
conditions. Air may be  supplied by mechanical or
diffused aeration to provide the oxygen required to
sustain the aerobic biological process. Mixing must
be provided by aeration or mechanical means to
maintain the microbial organisms in contact with
the dissolved organics. In addition, the pH must be
controlled to optimize the biological process and
essential nutrients must be present  to  facilitate
biological growth and the continuation of biological

As  depicted in Figure  1, wastewater enters the
treatment  system and is  typically  screened
                                            To Solids Handling,
                                              Disposal, or
                                             Beneficial Reuse
                                        Return Activated
                                         Sludge (RAS)
 Waste Activated
 Sludge (WAS)
                             Screening/  Flow   Extended  Clarification
                              Grinding Equalization  Aeration
                                  (if required)
                      Source: Parsons Engineering Science, 2000.

                         FIGURE 1 PROCESS FLOW DIAGRAM
                        FOR A TYPICAL EXTENDED AERATION
                      immediately to remove large suspended, settleable,
                      or floating  solids  that could interfere with or
                      damage  equipment downstream  in the process.
                      Wastewater may then pass through a grinder to
                      reduce large particles that are not captured in the
                      screening process. If the plant requires the flow to
                      be regulated,  the  effluent will  then  flow  into
                      equalization basins which regulate peak wastewater
                      flow rates.  Wastewater then enters the aeration
                      chamber, where it is mixed and oxygen is provided
                      to the microorganisms.  The mixed liquor  then
                      flows to  a clarifier or settling chamber where most
                      microorganisms settle to the bottom of the clarifier
                      and a portion are pumped back to the incoming
                      wastewater at the beginning of the plant.   This
                      returned material is the return activated sludge
                      (RAS).  The material that is not returned, the waste
                      activated sludge (WAS), is removed for treatment
                      and disposal.  The clarified wastewater then flows
                      over a weir and into a collection channel before
                      being diverted to the disinfection system.

Extended aeration package plants consist of a steel
tank  that  is  compartmentalized  into   flow
equalization,  aeration, clarification, disinfection,
and  aerated  sludge  holding/digestion segments.
Extended   aeration   systems  are  typically
manufactured  to  treat  wastewater  flow  rates
between 0.002 to 0.1 MGD. Use of concrete tanks
may be preferable for larger sizes (Sloan, 1999).

Extended aeration plants are usually  started up
using "seed sludge" from another sewage plant.  It
may take as many  as two to four weeks from the
time it is seeded for the plant to stabilize (Sloan,

Sequencing batch reactors

A sequencing batch reactor (SBR) is a variation of
the activated sludge process.  As a fill and draw or
batch process, all biological treatment phases occur
in a single tank.  This differs from the conventional
flow through activated sludge process in that SBRs
do not  require  separate tanks for aeration  and
sedimentation(Kappe, 1999). SBR systems contain
either two or more reactor tanks that are operated in
parallel, or one equalization tank and  one reactor
tank.   The type of tank used depends on the
wastewater flow characteristics (e.g. high or low
volume).  While this  setup allows  the system  to
accommodate continuous influent flow, it does not
provide for disinfection or holding  for aerated

There are many types of SBR systems, including
continuous influent/time  based,  non-continuous
influent/time based, volume based,  an  intermittent
cycle system (a SBR that utilizes jet aeration), and
various   other  system  modifications  based  on
different manufacturer designs. The type of SBR
system  used  depends on site  and  wastewater
characteristics as well as the needs of the area  or
community installing the unit.  Package SBRs are
typically manufactured to treat wastewater flow
rates between 0.01 and 0.2 MGD; although flow
rates  can   vary  based  on   the  system   and

As seen in Figure 2,  the influent flow first goes
through a screening process before entering the
SBR. The waste is then treated in a series of batch
phases within the  SBR to achieve the  desired
effluent concentration. The sludge that is wasted
from the SBR moves on to digestion and eventually
to solids handling, disposal, or beneficial reuse.
The treated effluent then moves to disinfection. An
equalization tank is typically  needed before the
disinfection unit in batch SBRs in order to store
large volumes of water. If the flow is not equalized,
a sizable filter may be necessary to accommodate
the large flow of water  entering the disinfection
system.  In addition, SBR systems typically have no
primary or secondary clarifiers as settling  takes
place in the SBR.
                 To Solids Handling,
                   Disposal, or
                  Beneficial Reuse
Source: Parsons Engineering Science, 2000.

            FOR A TYPICAL SBR
There  are normally  five phases  in the  SBR
treatment cycle: fill, react, settle, decant, and idle.
The  length  of time that each  phase occurs  is
controlled by  a  programmable logic controller
(PLC), which allows the system to be controlled
from remote  locations  (Sloan, 1999).  In the fill
phase, raw wastewater enters the basin, where it is
mixed with settled biomass from the previous cycle.
Some aeration may occur during this phase. Then,
in the react phase, the basin  is aerated, allowing
oxidation and nitrification to occur.  During the
settling phase, aeration and mixing are suspended
and the solids are allowed to settle.  The treated
wastewater is then discharged from the basin in the
decant phase. In the final phase, the basin is idle as
it waits for the start of the next cycle.  During this
time, part of the solids are removed from the basin
and disposed of as waste sludge (Kappe, 1999).
Figure 3 shows this  sequence of operation in an


Source: CASS Water Engineering, Inc., 2000.

Sludge wasting is an important  step in the  SBR
process and largely affects system performance. It
is not considered a basic phase since the sludge is
not wasted at a specific time period during the
cycle.   The  quantity and rate of  wasting is
determined by performance requirements. An SBR
system does not require an RAS system, as both
aeration and settling occur in the same tank.  This
prevents any sludge from being lost during the react
step and eliminates the need to return sludge from
the clarifier to the aeration chamber (Metcalf and
Eddy, 1991).

Oxidation ditches

An oxidation ditch,  a  modified form of the
activated sludge process, is an aerated, long term,
complete mix process. Many systems are designed
to operate as extended aeration systems.  Typical
oxidation ditch treatment systems consist of a single
or multi-channel configuration within a ring,  oval,
or  horseshoe-shaped  basin.     Horizontally  or
vertically  mounted  aerators  provide  aeration,
circulation, and oxygen transfer in the ditch.

Package   oxidation  ditches   are  typically
manufactured  in sizes that treat  wastewater flow
rates between 0.01 and 0.5 MGD.  As seen in
Figure 4, raw wastewater  is first screened before
entering the oxidation ditch.   Depending on the
system size and manufacturer type, a grit chamber
may be  required.   Once  inside the  ditch, the
wastewater is aerated with mechanical surface or
submersible aerators (depending on manufacturer
design)  that propel the  mixed liquor around the
channel at velocities high enough to prevent solids
deposition.   The  aerator  ensures that there is
sufficient oxygen in the fluid for the microbes and
adequate mixing to ensure constant contact between
the organisms  and the  food  supply  (Lakeside,
                                  To Solids Handling,
                                 Disposal, or Beneficial
Source: Parsons Engineering Science, 1999.

Oxidation ditches tend to operate in an extended
aeration  mode  consisting  of long hydraulic and
solids retention times which  allow  more organic
matter to break down. Treated sewage moves to the
settling tank or final clarifier, where the biosolids
and water separate.  Wastewater then moves to
other treatment processes while sludge is removed.
Part of it is returned to the ditch as RAS, while the
rest is removed from  the  process  as  the  waste
activated sludge (WAS).  WAS is  wasted  either
continuously or daily and must be stabilized prior to
disposal or beneficial reuse.


In general, package treatment plants  are applicable
for areas with a limited number of people and small
wastewater flows.   They are most  often used in
remote locations such as trailer parks, highway rest
areas, and rural areas.

Extended aeration plants

Extended aeration package plants are typically used
in small  municipalities,  suburban  subdivisions,
apartment complexes, highway rest areas, trailer

parks, small institutions, and other sites where flow
rates are below 0.1 MOD. These systems are also
useful for areas requiring nitrification.

Sequencing batch reactors

Package plant SBRs are suitable for areas with little
land, stringent treatment requirements, and  small
wastewater  flows.  More specifically,  SBRs  are
appropriate  for  RV parks  or  mobile  homes,
campgrounds,  construction  sites, rural  schools,
hotels, and other small applications. These systems
are also useful for treating pharmaceutical, brewery,
dairy, pulp and paper, and chemical wastes. While
constant cycles with time-fixed process phases are
sufficient  in  most cases,  phases  should  be
individually adapted and optimized for each plant.
SBRs are also  suited for sites that need minimal
operator attendance and that have a wide range of
inflow and/or organic loadings.

Industries with  high  BOD  loadings, such as
chemical or food processing plants, will find SBRs
useful for treating wastewater. These systems are
also  suitable for facilities  requiring nitrification,
denitrification,  and  phosphorous  removal.   Most
significantly, SBRs are applicable for areas where
effluent  requirements can change frequently and
become stricter, as these systems have tremendous
flexibility to change treatment options.  However,
part of the economic advantage of the SBR process
is lost when  advanced treatment processes must be
added downstream since intermediate equalization
is normally required.

Oxidation ditches

Oxidation ditches are  suitable for facilities that
require nutrient removal, have limitations due to the
nature of the site, or want a biological system that
saves energy with limited use of chemicals unless
required for further treatment.   Oxidation  ditch
technology  can be  used to  treat any type of
wastewater   that  is   responsive  to  aerobic
degradation.  In addition, systems can be designed
for denitrification and phosphorous removal.

Types  of industries utilizing  oxidation  ditches
include: food processing, meat and poultry packing,
breweries,    pharmaceutical,   milk  processing,
petrochemical,  and   numerous   other   types.
Oxidation  ditches  are  particularly  useful  for
schools,  small  industries, housing developments,
and small communities. Ultimately, this technology
is  most  applicable  for  places that have  a large
amount of land available.


Some advantages and disadvantages  of package
plants are listed below.

Extended aeration plants


•  Plants are easy to operate, as many are manned
   for a maximum of two or three hours per day.

•  Extended aeration processes are often better at
   handling organic loading and flow fluctuations,
   as there is  a greater  detention time  for  the
   nutrients to be assimilated by microbes.

•  Systems are easy to install, as they are shipped in
   one or two pieces and then mounted on an onsite
   concrete pad, above or below grade.

•  Systems are odor free, can be installed in most
   locations, have a relatively small footprint, and
   can be  landscaped to  match the surrounding

•  Extended aeration systems have a relatively low
   sludge yield  due to long sludge ages, can be
   designed to provide nitrification,  and do  not
   require a primary clarifier.


•  Extended  aeration  plants  do not  achieve
   denitrification or phosphorus removal without
   additional unit processes.

•  Flexibility  is limited  to adapt to  changing
   effluent requirements resulting from regulatory

•  A longer aeration period requires more energy.

•  Systems require a larger amount of space and
   tankage than  other  "higher  rate"  processes,
   which have shorter aeration detention times.

Sequencing batch reactors


•  SBRs can consistently perform nitrification as
   well as denitrification and phosphorous removal.

•  SBRs have large operational flexibility.

•  The ability to  control substrate tension within
   the system allows for optimization of treatment
   efficiency  and control over nitrogen removal,
   filamentous organisms, and the overall stability
   of the process.

•  Since all the unit processes are operated in a
   single tank, there is no need to optimize aeration
   and   decanting   to  comply  with  power
   requirements and lower decant discharge rates.

•  Sludge bulking is not a problem.

•  Significant reductions in nitrate nitrogen can
   occur by incorporating an anoxic cycle in the

•  SBRs have  little operation and  maintenance

•  Systems  require  less  space  than  extended
   aeration plants of equal capacity.

•  SBRs can be manned part time from remote
   locations, and operational changes can be made

•  The system  allows for automatic  and positive
   control  of  mixed liquor  suspended  solids
   (MLSS) concentration and solids retention time
   (SRT) through the use of sludge wasting.


•  It is  hard to adjust the  cycle  times for small
•  Post equalization may be required where more
   treatment is needed.

•  Sludge must be disposed frequently.

•  Specific energy consumption is high.

Oxidation ditches


•  Systems  are  well-suited for treating  typical
   domestic  waste,   have   moderate   energy
   requirements, and work effectively under most
   types of weather.

•  Oxidation  ditches  provide  an  inexpensive
   wastewater treatment option with both low
   operation and maintenance costs and operational

•  Systems can be used with or without clarifiers,
   which affects flexibility and  cost.

•  Systems  consistently  provide   high  quality
   effluent in terms of TSS, BOD, and ammonia

•  Oxidation ditches have a relatively low sludge
   yield, require a moderate amount of operator
   skill, and are  capable of handling  shock and
   hydraulic loadings.


•  Oxidation  ditches  can  be  noisy  due  to
   mixer/aeration equipment, and tend to produce
   odors when not operated correctly.

•  Biological treatment is unable to treat highly
   toxic waste streams.

•  Systems have a relatively large footprint.

•  Systems have less flexibility should regulations
   for effluent requirements change.


Table 1 lists typical design parameters for extended
aeration plants, SBRS, and oxidation ditches.


                  Extended   SBR   Oxidation
                  Aeration            Ditch
BOD5 loading
(Ib BOD5/ Ib
Avg. at 20- C
(Ib/lb BOD5
Peak at 20- C
(value x avg.
0.05-0.15 0.05- 0.05-030
2-3 2-3 2-3
1.5-2.0 1.25- 1.5-2.0
 MLSS (mg/L)      3000-6000   1500   3000-6000
Detention Time
(Ib BOD5/d/ 103
18-36 16- 18-36
10-25 5-15 5-30
Source:  Adapted from Metcalf and Eddy, 1991 and
WEF, 1998.
Extended aeration plants

Package  extended  aeration plants are typically
constructed from steel or concrete.  If the system is
small enough, the entire system will arrive as one
unit that is ready to be installed.  If the system is
larger, the clarifier, aeration chamber, and chlorine
tank are delivered as separate units, which are then
assembled on-site (WEF, 1985).

Key  internal components  of extended  aeration
treatment plants consist of the following: transfer
pumps  to   move  wastewater  between  the
equalization and aeration zones; a bar screen and/or
grinder to  decrease the size of large solids; an
aeration system consisting of blowers and diffusers
for the equalization, aeration, and sludge holding
zones; an  airlift pump  for returning sludge;  a
skimmer and effluent weir for the clarifier; and UV,
liquid hypochlorite, or tablet modules used in the
disinfection zone.  Blowers and the control panel
containing  switches, lights, and motor starters are
typically attached to either the top or one side of the
package plant (Sloan, 1999).

Biological  organisms  within   the  system  need
sufficient contact time with the organic material in
order to produce effluent of an acceptable quality.
Typical contact time for extended aeration package
plants is approximately 18-24 hours. The contact
time,  daily flow rate, influent parameters,  and
effluent parameters   determine the size  of the
aeration tank where air is used to mix wastewater
and to supply oxygen to promote biological growth.
A package  extended aeration system is sized based
on the average volume  of wastewater  produced
within a twenty-four hour  period.    Although
provisions are made for some peaking factor, a flow
equalization system may be necessary to prevent
overloading of the system from inconsistent flow
rates  in the morning and evening.   Equalization
allows the wastewater  to be  delivered  to the
treatment  plant  at  more manageable flow rates
(WEF, 1985).

Systems  should  be installed  at   sites   where
wastewater collection is possible by gravity  flow.
In addition, the site should be stable, well drained,
and not prone to flooding.  The facility should be
installed at least 30 meters (100  feet) from  all
residential  areas and be in accordance with  all
health department regulations or zoning restrictions
(WEF, 1985).

In  order   to  ensure  ease  of  operation  and
maintenance, extended aeration  systems should be
installed so that the tank  walls extend nearly 0.15
meters (6 inches) above ground. This will supply
insulation in the winter, prevent surface runoff from
infiltrating  the system, and allow the system to be
serviced readily.   If a  plant  is  installed  below
ground, it must have distinct diversion ditching or
extension walls in order  to prevent  surface water
infiltration  into  the plant.  When  the plant is
installed completely  above ground,  it may  be

necessary to provide insulation for cold weather and
walkways for easy maintenance (WEF, 1985).

Sequencing batch reactors

Important internal components include an aeration
system, which typically consists of diffusers and a
blower; a floating mixer;  an effluent decanter; a
pump for withdrawing sludge; and a sequence of
liquid level floats.  The PLC and the control panel
are usually positioned  within a  nearby  control
building (Sloan, 1999).

When the wastewater flow rate at the site is less
than 0.05 MGD, a single,  prefabricated steel tank
can be used.   This tank is divided into one SBR
basin, one aerobic sludge digester,  and one influent
pump well. Concrete tanks may also be used, but in
North America are not as cost effective as steel for
small systems. If the plant must be able to treat 0.1
to 1.5 MGD,  multiple  concrete  SBR basins are
commonly used (CASS, 1999).

The  design of SBR systems can be based  on
carbonaceous  BOD  removal   only  or  both
carbonaceous and nitrogenous BOD removal. The
system  can be  expanded to achieve  optimum
nitrification and carbonaceous removal by operating
primarily in an oxic state with few anoxic periods
such as during settle and decant.

Denitrification and biological phosphorous removal
can be  promoted by providing  adequate anoxic
periods after intense aerobic cycles.  This allows
DO to be dissipated and nitrate to be used by the
consuming organism and  released as elemental
nitrogen. By introducing an anaerobic process after
the anoxic process, bacteria conducive to excess
phosphorous  uptake will  develop.  Phosphorous
will  be  released in the   anaerobic  phase,  but
additional phosphorous is incorporated into the cell
mass during subsequent aerobic cycles. Since the
excess phosphorous is incorporated in the cell mass,
cell wastage must be practiced to achieve a net
phosphorous removal. Anaerobic conditions should
be avoided in treating the  waste sludge since they
may result in the release of the phosphorous.

A low  food to microorganism (F:M) ratio SBR
system  designed  for  an average  municipal flow
pattern  will  usually have an  operating  cycle
duration of four hours, or six cycles per day. For a
two reactor system, there will be twelve cycles per
day and for  a  four  reactor system, twenty-four
cycles per day.   The distribution and number of
cycles per day can be adjusted based on specific
treatment requirements or to accommodate alternate
inflow patterns.

Cycle sequences are time controlled with sufficient
volume  provided to handle design flow rates.  If
incoming flow is significantly less than the design
flow,  only a portion of the reactor capacity is
utilized and aeration time periods can be reduced to
save energy and prevent over aeration. If flow rates
are greater than usual resulting from storm runoff,
the control system detects the high rise in the
reactor  and modifies the cycle to integrate  peak
flow rates.  This will shorten the aeration, settle,
and  decant  sequences,  minimize  the  anoxic
sequence (if supplied), and provide more cycles per
day.  As a result, hydraulic surges are incorporated
and the diluted wastewater is processed in less time.
In order to make the above optimizations, the logic
control  must be provided  by the PLC  (Kappe,

Small SBRs can experience a variety of problems
associated  with operation,   maintenance,  and
loadings.  Therefore, more conservative design
criteria are typically used due to the wide range of
organic  and hydraulic loads generated from small
communities.  This type of design utilizes a lower
F:M ratio  and  longer  hydraulic retention  time
(HRT) and SRT (CASS, 1999).

Oxidation ditches

Key  components  of a  typical  oxidation ditch
include  a screening device, an influent distributor
(with some systems), a basin or channel, aeration
devices  (mechanical aerators,  jet  mixers,  or
diffusers,  depending on the  manufacturer),   a
settling tank or final clarifier (with some systems),
and  an RAS   system  (with  some   systems).
Typically,  the  basin   and  the   clarifier  are
individually sized to meet the specific  requirements
of each facility.  These components are often built
to share a common wall in order to reduce costs and
save space (Lakeside, 1999).

Concrete tanks are typically used when installing
package plant oxidation ditches.  This results in
lower maintenance costs as concrete tanks do not
require  periodic  repainting or  sand  blasting.
Fabricated  steel or a  combination  of steel  and
concrete  can  also  be used  for  construction,
depending on site conditions (Lakeside, 1999).

The volume of the oxidation ditch is  determined
based  on  influent  wastewater  characteristics,
effluent  discharge   requirements,  HRT,  SRT,
temperature,   mixed   liquor  suspended   solids
(MLSS), and pH. It may be necessary to include
other   site  specific  parameters  to  design  the
oxidation ditch as well.

Some oxidation ditches do not initially require
clarifiers, but can later be upgraded and expanded
by adding clarifiers, changing the type of process
used, or adding additional ditches (Kruger, 1999).


The performance of package plants in general can
be affected by various operational and design issues
(Metcalf and Eddy, 1991).

•  Large and  sudden temperature changes

•  Removal efficiency of grease and scum from the
   primary  clarifier (except with oxidation ditches
   that do not use primary clarifiers)

•  Incredibly small flows that make designing self-
   cleansing conduits and channels difficult

•  Fluctuations in flow, BOD5 loading, and other
   influent parameters

•  Hydraulic shock loads, or the large fluctuations
   in flow from small communities

•  Sufficient control of the air supply rate

Extended aeration plants

Extended   aeration  plants  typically  perform
extremely well and achieve effluent quality as seen
in Table 2.  If chemical precipitation is used, total
phosphorous (TP) can be < 2 mg/L. In some cases,
extended aeration systems result in effluent with
< 15 mg/L BOD and < 10 mg/L TSS.


                   Typical       Aldie WWTP
                   Effluent        (monthly
                   Quality         average)
BOD (mg/L)
TSS (mg/L)
TP (mg/L)
NH3-N (mg/L)
< 30 or<10
< 30 or<10
* May require chemicals to achieve.
** DEQ does not require monitoring of these parameters.
Source: Sloan, 1999 and Broderick, 1999.

Aldie Wastewater Treatment Plant

The Aldie Wastewater Treatment Plant, located in
Aldie,  Virginia, is an extended aeration  facility
which treats an average  of 0.0031 MGD with a
design flow of 0.015  MGD. This technology was
chosen because it would allow the area to  meet
permit requirements  while minimizing land use.
The  plant consists of an influent chamber which
directs the flow to two  parallel aeration  basins,
parallel clarifiers, and a UV disinfection system.

Sequencing batch reactors

The treatment performance of package plant SBRs
is largely influenced by the plant operator. While
the  process  requires  little  assistance,  training
programs are available to teach operators  how to
become skilled  with small plant operations.  SBRs
perform well, often matching the removal efficiency
of extended  aeration processes.   Systems  can
typically achieve the effluent limitations listed in

In addition, SBR systems have demonstrated  a
greater removal efficiency of carbonaceous BOD
than other systems due to optimization of microbial
activity via anoxic stress and better utilization of
applied oxygen in the cyclic system.   The system
can  consistently  provide  carbonaceous  BOD
effluent levels of 10 mg/L.

Harrah WWTP
BOD (mg/L)
TSS (mg/L)
NH3 (mg/L)
< 1
 Source: Sloan, 1999 and Reynolds, 1999.

Harrah Wastewater Treatment Plant

The   Harrah  wastewater  treatment  plant  in
Oklahoma treats an average wastewater flow of
0.223  MOD.   The  SBR has  achieved  tertiary
effluent quality without filtration from the time it
was first installed. Pretreatment involves an aerated
grit chamber and comminutor.   Waste activated
sludge is taken to a settling pond where the settled
sludge is dredged annually.  A nitrogen removal
study performed for nine months confirmed that
nitrification and  denitrification occur consistently
without special operator care.

Oxidation Ditches

Although the manufacturer's design may vary, most
oxidation  ditches typically achieve the effluent
limitations listed in Table 4.  With modifications,
some oxidation ditches can achieve TN removal to
• 5 mg/L and TP removal with biological means.

City of Ocoee Wastewater Treatment Plant

Currently, the wastewater treatment plant in Ocoee,
Florida accepts an average flow of 1.1 to 1.2 MOD.
The city chose to use an oxidation ditch because it
was  an easy  technology  for the  plant staff to
understand and  implement.  The  facility  is  also
designed for denitrification  without the use of
chemical additives. Nitrate levels consistently test
at 0.8 to 1.0 mg/L with limits of 12 mg/L (Holland,
1999).  Table 4 indicates how well  the Ocoee
oxidation ditch performs.
                                                 Ocoee WWTP
          With 2°   With      %
          Clarifier   Filter   Removal
Note: 2° = secondary. NA = not available.
Source: Kruger, 1999 and Holland, 1999.


Operation requirements  will  vary  depending on
state requirements for manning package treatment
systems.  Manning requirements for these systems
may typically be less then eight hours a day.  Each
type  of  system   has   additional   operational
procedures that should be  followed to keep the
system running properly. Owners of these systems
must  be  sure  to   follow  all  manufacturer's
recommendations for routine  and preventative
maintenance requirements.   Each  owner should
check with the manufacturer to determine essential
operation and maintenance (O&M) requirements.

Depending on state  requirements,  most systems
must submit regular reports to local agencies. In
addition, system operators  must  make safety a
primary concern.  Wastewater treatment manuals
and federal and state regulations should be checked
to ensure safe operation of these systems.

Extended aeration plants

Operational procedures for these systems consist of
performing fecal coliform tests on the effluent to
ensure adequate disinfection and making periodic

inspections on dissolved oxygen levels (DO) and
MLSS concentrations in the aeration compartment.
Sludge-volume  index  (SVT) tests in the clarifier
must also be performed to determine how well the
sludge is settling. Other sampling and analyses will
be required on the effluent in accordance with state

Typical  maintenance steps  for  extended aeration
systems include checking motors, gears, blowers,
and  pumps  to  ensure proper lubrication  and
operation. Routine inspection of equipment is also
recommended to ensure proper  operation. Check
with  the  manufacturer   for   specific  O&M

Sequencing batch reactors

To ensure proper functioning of the system, O&M
must be provided for several pieces of equipment.
Operational  procedures  include sampling   and
monitoring  of  DO,  pH,   and  MLSS  levels.
Additional  sampling and  analyses on the effluent
will be required based on state regulations.

Maintenance requirements include regular servicing
of aeration blowers,  which is usually  performed
when greasing is done, and monthly inspection of
belts on the blowers to determine if they need to be
adjusted or replaced.  Submersible pumps require
routine inspections and servicing as required by the
manufacturer. The decanter will require  monthly
greasing.   Additional O&M  may  be  required
depending on system requirements. Check with the
manufacturer   for   specific   maintenance

Oxidation ditches

Depending on the manufacturer's design, typical
operational procedures for oxidation ditches include
monitoring of DO, pH, MLSS,  and various other
types of sampling and analyses.

Maintenance  steps include  periodically inspecting
the aerator, regularly greasing rotors, and following
manufacturer recommendations for maintenance of
the  pumps.     Operators  should  follow  all
manufacturer recommendations  for operation and
maintenance of the equipment.

Costs are site specific and generally depend on flow
rate, influent wastewater characteristics, effluent
discharge  requirements,  additional   required
equipment, solids handling equipment, and other
site specific conditions.  Manufacturers should be
contacted for specific cost information.

Extended aeration plants

As  provided by Aeration Products, Inc., smaller
extended aeration package plants designed to treat
less than 0.02 MOD cost approximately $4 to $6
per gallon of water treated, based on capital costs.
For  larger  plants,   capital   costs   will   be
approximately between $2 to $2.50 per gallon of
wastewater treated. Maintenance processes forthese
plants are labor-intensive and require semi-skilled
personnel,  and  are  usually  completed  through
routine  contract services.     Maintenance  cost
averages $350 per year.

Table 5 provides the cost  estimates for various
extended aeration packages.  These costs include
the entire package plant, as well as a filtration unit.

      Flow (MGD)
Estimated Budget
Cost per Gallon ($)
 Note:  Larger  flow  rates  are  available  from  the
 manufacturer. Estimated cost per gallon was determined
 based on the mid-flow range.

 Source: Parsons Engineering Science, 1999.
Sequencing batch reactors

The capital cost per capita for small SBR plants is
greater than for  large SBR plants.  Approximate
equipment costs disregarding concrete or steel tanks
costs are provided in Table 6.  Operation energy
costs are likely to be higher for small  SBR plants
than for larger  plants as a result of numerous

                            TABLE 7 COST ESTIMATES FOR
                                   OXIDATION DITCHES
      Flow (MGD)
Estimated Budget
Cost per Gallon ($)
 Note:  Larger  flow  rates  are  available  from  the
 manufacturer.  Estimated cost per gallon was determined
 based on the mid-flow range.

 Source: CASS, 1999.
System costs will vary, depending on the specific
job.  Factors influencing cost include average and
peak flow, tank type, type of aeration system used,
effluent  requirements,   and   site  constraints.
Operation and maintenance costs are site specific
and may range from $800 to $2,000 dollars per
million gallons treated.  Labor  and maintenance
requirements may be reduced in SBRs because
clarifiers and RAS pumps may not be necessary.
On the other hand, maintenance requirements for
the  more   sophisticated  valves   and  switches
associated with SBRs may be more costly than for
other systems.

Oxidation ditches

Table 7 lists budget cost estimates for various sizes
of oxidation ditches. Operation and maintenance
costs for oxidation ditches are significantly  lower
than other  secondary treatment  processes.  In
comparison to other treatment technologies, energy
requirements are low, operator attention is minimal,
and chemical addition is not required.


Other Related Fact Sheets

Sequencing Batch Reactors
EPA 932-F-99-073
September 1999
Flow Range
1.1 -1.7
Budget Price
Budget Cost
per Gallon ($)
                         Note:  Larger  flow  rates  are  available  from  the
                         manufacturer. Estimated cost per gallon was determined
                         based on the mid-flow range.

                         Source: Lakeside, 1999.
                        Oxidation Ditches
                        EPA 832-F-00-013
                        September 2000

                        Aerobic Treatment
                        September 2000

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

                        1.     Broderick, T., 1999.  Aldie  Wastewater
                              Treatment Plant, Aldie, Virginia. Personal
                              communication with Dacia Mosso, Parsons
                              Engineering Science, Inc.

                        2.     CASS  Water  Engineering,  Inc.,  2000.
                              Literature provided by manufacturer.

                        3.     Crites, R.  and G. Tchobanoglous,  1998.
                              Small  and  Decentralized  Wastewater
                              Management Systems. WCB McGraw-Hill,
                              Inc. Boston, Massachusetts.

                        4.     Holland,   R,   1999.   City   of  Ocoee
                              Wastewater  Treatment  Plant,  Ocoee,
                              Florida.    Personal  communication  with
                              Dacia Mosso, Parsons Engineering Science,

Hydro-Aerobics, July 1999.
provided by manufacturer.
Kappe Associates Engineered  Systems,
Frederick,  Maryland,  1999.  Literature
provided by distributor.

Kruger, July 1999. Literature provided by

Lakeside, July 1999. Literature provided by

Metcalf & Eddy,  Inc.,  1991. Wastewater
Engineering:  Treatment,  Disposal,  and
Reuse.   3rd   ed.  The   McGraw-Hill
Companies. New York, New York.

Reynolds, S., 1999. US Filter Jet Tech,
Edwardsville,    Kansas.     Personal
communication with Dacia Mosso, Parsons
Engineering Science.

Sloan Equipment, Owings Mills, Maryland,
1999. Literature provided by distributor and
manufacturer (Aeration Products, Inc.).

Water Environment  Federation  (WEF),
1998.  Design  of Municipal Wastewater
Treatment Plants. Manual of Practice No. 8.
4th ed. vol. 2. WEF. Alexandria, Virginia.

Water Environment  Federation  (WEF),
1985.  Operation  of Extended  Aeration
Package Plants. Manual of Practice No.
OM-7. WEF. Alexandria, Virginia.
Mr. Mike Lynn
Onsite Solutions
P.O. Box 570
Nokesville, Virginia 20182

Sequencing batch reactors

Steve Giarrusso
213 Osborne Street

Steven Urich
Facility Manager
Medley Pretreatment Facility
9431 Live Oak Place
Suite 309
Ft. Lauderdale, FL 33324

Oxidation ditches

Robert Holland
Utilities Superintendent
Ocoee Wastewater Treatment Plant
1800 A. D. Minis Road
Ocoee, FL 34761

Michael Eldredge
Chief Operator
Edgartown Wastewater Department
P.O. Box 1068
Edgartown, MA 02539

The  mention  of trade names  or  commercial
products  does  not constitute endorsement or
recommendation for use by the U.S. Environmental
Protection Agency.
Extended aeration plants

Ted Jackson (O&M)
Tim Coughlin (General questions)
Manager Engineering Programs
Aldie WWTP
P.O. Box 4000
Leesburg, VA20177
                                                    For more information contact:

                                                    Municipal Technology Branch
                                                    U.S. EPA
                                                    Mail Code 4204
                                                    1200 Pennsylvania Avenue, NW
                                                    Washington, D.C. 20460
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