vvEPA
United States
Environmental Protection
Agency
Office of Water
Washington, D.C.
EPA832-F-00-016
September 2000
Waste water
Technology Fact Sheet
Package Plants
DESCRIPTION
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
degradation.
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)
Digestion
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
PLANT
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.
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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,
1999).
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
sludge.
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
manufacturer.
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
Digestion
Disinfection
Source: Parsons Engineering Science, 2000.
FIGURE 2 PROCESS FLOW DIAGRAM
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
SBR.
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Decant
Decanter
Effluent
Discharge
Source: CASS Water Engineering, Inc., 2000.
FIGURE 3 SBR SEQUENCE OF
OPERATION
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,
1999).
Digestion
To Solids Handling,
Disposal, or Beneficial
Reuse
Screenim
Grinding
Source: Parsons Engineering Science, 1999.
FIGURE 4 PROCESS FLOW DIAGRAM
FOR A TYPICAL OXIDATION DITCH
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.
APPLICABILITY
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
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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.
ADVANTAGES AND DISADVANTAGES
Some advantages and disadvantages of package
plants are listed below.
Extended aeration plants
Advantages
• 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
area.
• 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.
Disadvantages
• 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
changes.
• A longer aeration period requires more energy.
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• Systems require a larger amount of space and
tankage than other "higher rate" processes,
which have shorter aeration detention times.
Sequencing batch reactors
Advantages
• 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
system.
• SBRs have little operation and maintenance
problems.
• 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
easily.
• 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.
Disadvantages
• It is hard to adjust the cycle times for small
communities.
• Post equalization may be required where more
treatment is needed.
• Sludge must be disposed frequently.
• Specific energy consumption is high.
Oxidation ditches
Advantages
• 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
needs.
• 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
levels.
• Oxidation ditches have a relatively low sludge
yield, require a moderate amount of operator
skill, and are capable of handling shock and
hydraulic loadings.
Disadvantages
• 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.
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DESIGN CRITERIA
Table 1 lists typical design parameters for extended
aeration plants, SBRS, and oxidation ditches.
TABLE 1 TYPICAL DESIGN
PARAMETERS FOR PACKAGE PLANTS
Extended SBR Oxidation
Aeration Ditch
BOD5 loading
(F:M)
(Ib BOD5/ Ib
MLVSS)
Oxygen
Required
Avg. at 20- C
(Ib/lb BOD5
applied)
Oxygen
Required
Peak at 20- C
(value x avg.
flow)
0.05-0.15 0.05- 0.05-030
0.30
2-3 2-3 2-3
1.5-2.0 1.25- 1.5-2.0
2.0
MLSS (mg/L) 3000-6000 1500 3000-6000
-5000
Detention Time
(hours)
Volumetric
Loading
(Ib BOD5/d/ 103
cuft)
18-36 16- 18-36
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
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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,
1999).
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).
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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).
PERFORMANCE
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.
TABLE 2 EXTENDED AERATION
PERFORMANCE
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
<2*
<2
5
17
**
**
* 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
Tables.
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.
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TABLES SBRPERFORMANCE
TABLE 4 OXIDATION DITCH
PERFORMANCE
Typical
Effluent
Harrah WWTP
Removal
Effluent
BOD (mg/L)
TSS (mg/L)
NH3 (mg/L)
10
10
< 1
98
98
97
3
3
0.6
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.
Typical
Effluent
Quality
Ocoee WWTP
With 2° With %
Clarifier Filter Removal
Effluent
CBOD
(mg/L)
TSS
(mg/L)
TP
(mg/L)
N-NO3
(mg/L)
•10
•10
2
NA
5
5
1
NA
>97
>97
NA
>95
4.8
0.32
NA
0.25
Note: 2° = secondary. NA = not available.
Source: Kruger, 1999 and Holland, 1999.
OPERATION AND MAINTENANCE
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
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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
regulations.
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
requirements.
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
requirements.
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
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 $350 per year.
Table 5 provides the cost estimates for various
extended aeration packages. These costs include
the entire package plant, as well as a filtration unit.
TABLE 5 COST ESTIMATES FOR
EXTENDED AERATION
Flow (MGD)
Estimated Budget
Cost per Gallon ($)
0.015
0.04
1.0
9-11
7
1.3
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
loadings.
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TABLE 6 COST ESTIMATES FOR SBRs
TABLE 7 COST ESTIMATES FOR
OXIDATION DITCHES
Flow (MGD)
Estimated Budget
Cost per Gallon ($)
0.01
0.05
0.2
1.0
4-5
2
0.7
0.25
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 $2,000 dollars per
million gallons treated. Labor and maintenance
requirements may be reduced in SBRs because
clarifiers and RAS pumps may not be necessary.
On the other hand, maintenance requirements for
the more sophisticated valves and switches
associated with SBRs may be more costly than for
other systems.
Oxidation ditches
Table 7 lists budget cost estimates for various sizes
of oxidation ditches. Operation and maintenance
costs for oxidation ditches are significantly lower
than other secondary treatment processes. In
comparison to other treatment technologies, energy
requirements are low, operator attention is minimal,
and chemical addition is not required.
REFERENCES
Other Related Fact Sheets
Sequencing Batch Reactors
EPA 932-F-99-073
September 1999
Flow Range
(MGD)
0-0.03
0.03-0.06
0.06-1.1
1.1 -1.7
1.7-2.5
Budget Price
($)
80,000
91,000
97,500
106,000
114,700
Estimated
Budget Cost
per Gallon ($)
5.33
2.02
0.17
0.08
0.05
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
EPA832-F-00-031
September 2000
Other EPA Fact Sheets can be found at the
following web address:
http://www.epa.gov/owmitnet/mtbfact.htm
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,
Inc.
-------
5.
6.
7.
Hydro-Aerobics, July 1999.
provided by manufacturer.
Literature
9.
10.
Kappe Associates Engineered Systems,
Frederick, Maryland, 1999. Literature
provided by distributor.
Kruger, July 1999. Literature provided by
manufacturer.
Lakeside, July 1999. Literature provided by
manufacturer.
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.
ADDITIONAL INFORMATION
11.
12.
13.
Mr. Mike Lynn
Onsite Solutions
P.O. Box 570
Nokesville, Virginia 20182
Sequencing batch reactors
Steve Giarrusso
Operator
213 Osborne Street
Minoa,NY13116
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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