vvEPA
United States
Environmental Protection
Agency
Office of Water
Washington, D.C.
EPA 832-F-00-067
September 2000
Biosolids and Residuals
Management Fact Sheet
Odor Control in Biosolids Management
DESCRIPTION
This Fact Sheet provides information on the control
of odors from biosolids production facilities, and
the prevention of odors from the storage,
distribution, and application of the biosolids
product. The level of detail is intended to provide
an overview for decision-makers including
wastewater treatment plant managers and authority
managers. The information provided is not
intended to be design guidance.
Nuisance odors are a common occurrence at
wastewater treatment plants, biosolids processing
facilities, and biosolids recycling locations where
proper management and control are not
implemented. Failure to acknowledge the potential
for odors and to work to prevent odor emissions can
result in complaints, shutdowns, expensive retrofits,
and non-acceptance of the finished product. Every
operation should keep a systematic record of odor
complaints.(Chlupsa) Proper facility design,
operation, management, control and careful
oversight are necessary to minimize odors. Water
quality professionals have a responsibility to
mitigate nuisance odors.
The most successful odor control programs are
those that take a holistic approach and examine the
complete system from sewer users to land
application practices. Just as a good physician can
identify the cause of the illness and not just treat the
symptoms, effective odor management will identify
and manage the source of odors and not just attempt
to mask or hide the offensive odors. In addition, a
holistic approach will encompass effective
communications with those groups that may be
negatively impacted by odors.
Nuisance odors can have detrimental effects on
aesthetics, property values, and the quality of life in
communities subjected to them. There are odorous
compounds that are classified as toxic pollutants,
but emissions of these compounds are restricted by
air quality regulations and their control is not part
of this discussion. An odorous biosolids product,
or a biosolids treatment process that results in odor
emissions, may be perceived as unhealthy due to the
origin of the solids. The cause of health complaints
in the absence if irritation or toxicity is poorly
understood. (Schiffman et, al.) Tangential
information is available from other industries but
there is no necessarily direct relevance to biosolids
odors. More research is needed to identify potential
health effects of biosolids odors.
Odor complaints at operating facilities can lead to
long term problems. Local public opposition can
delay or prevent expansions or upgrades to facilities
required to improve water quality. The anticipation
of nuisance odors from proposed land application
programs can limit the implementation of a
worthwhile beneficial reuse program.
Why Do Biosolids Generate Odors?
The beauty of biosolids is that is an abundant
source of food for microorganisms including
protiens amino acids and carbohydrates. These
beasts in biosolids degrade these energy sources
and odorous compounds are formed. (Walker,
1991) Organic and inorganic forms of sulfur,
mercaptans, ammonia, amines, and organic fatty
acids are identified as the most offensive odor
causing compounds associated with biosolids
production. These compounds typically are
released from the biosolids by heat, aeration and
digestion. The odors vary by the type of residual
solids processed and the method of processing.
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Anaerobic digestion of primary wastewater
residuals produces hydrogen sulfide and other
sulfur-containing gases, while alkaline stabilization
of the solids volatilizes ammonia along with other
volatile compounds. Composting odors can be
caused by (Walker) ammonia, amine, sulfur-based
compounds, fatty acids, aromatics and
hydrocarbons such as terpenes from the wood
products used as bulking agents. Aerobically
digested and air-dried biosolids may contain little
hydrogen sulfide, but have mercaptan and dimethyl
sulfide odors.(Bertucci, Dodd, Hatfield, Williams)
The five independent factors that are required for
the complete odor assessment are:
1. Intensity or pervasiveness- a measure of the
perceived strength of the odor compared to
concentrations of a standard compound.
2. Character - which relates to the mental
association made by the subject in sensing
the odor.
3. Hedonics - the relative pleasantness or
unpleasantness of an odor sensed by the
subject.
4. Detectability or quantity - the number of
dilutions required to reduce an odor to its
minimum detectable threshold odor
concentration (Switzenbaum et al., 1997,
Walker).
5. Mass - total mass per unit time or the
volume of odorous air produced.
APPLICABILITY
Odor Control at Biosolids Processing Facilities
Biosolids processors are faced with odors during
thickening, digestion, dewatering, conveying,
storage, truck loading, air drying, composting, heat
drying, alkaline stabilization, and/or incineration.
The odors may be point sources or ambient air (in
a belt press room for example.) The odors may
emanate from point sources or be present in
ambient air from area sources. A comprehensive
odor audit and air dispersion modeling is the best
assurance that capital and operating dollars are
spent wisely. Facility owners should look for a
consultant who specializes in biosolids odor control
when initiating an odor audit. An odor audit will
accomplish the following:
• Quantify odors from each odor emissions
source.
Analyze for odor causing compounds.
• Determine the processes by which odor
causing compounds are formed.
• Identify the most significant odor sources.
• Obtain data for odor emissions air
dispersion modeling.
• Determine the most cost effective odor
management plan.
Good management practices or modification to the
operation may reduce odor emissions; however,
odor containment and treatment at the biosolids
processing facility may be necessary to control
downwind effects.
The value of air dispersion modeling prior to final
design should not be underestimated. Information
obtained from modeling may result in design
changes such as; increasing stack height, increasing
stack velocity, providing reheat to increase thermal
buoyancy, or dilution with ambient air. (Haug,
1990) These low cost features can save
significantly on capital and operating costs and
improve effectiveness.
Likewise, effective communication with the
affected community is important to enhance odor
management and reduce the number of complaints.
Odor Control at Land Application Sites
The biosolids producer should accept responsibility
for odor control at land application sites. Even if
the producer hires a contractor to provide
transportation, storage, or land application services,
the terms of the agreement should include
management practices to minimize odors. In
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addition, the generator and contractor should have
an odor response plan in place to provide guidance
and policy on documenting and responding to odor
complaints. The land applier should have the
ability and responsibility to divert biosolids from a
site that is experiencing odor problems.
Biosolids producers should make every effort to
minimize odors at the application site because the
long term efficacy of land application depends on it.
A dramatic increase in local ordinances that ban or
restrict the use of biosolids has been observed in
recent years as a result of odor complaints. A
nationwide survey (Biocycle 1999 revealed that
odors at land application sites were usually the
initial operating problem that resulted in
complaints, which were followed by questions and
often, organized public opposition.
Federal Biosolids Regulations do not regulate odors
because it was believed that odors from land
application did not present human health effects. It
has been said, however; "Biosolids odors may not
pose a health threat, but odors are killing public
support for biosolids recycling programs." (Toffey,
1999)
The most cost-effective approach to odor control
may be to examine the operation and maintenance
practices at the processing facility. Septic
conditions may result in a biosolids product that is
more offensive than necessary. Some polymers
break down into odor forming compounds under
high heat and elevated pH. Incomplete anaerobic
digestion can result in worse odors than no
digestion at all. Blending of raw and WAS prior to
liquid storage can result in higher concentrations of
Dimethyl Sulfide. (Hentz and Cassel, 2000)
Methods to reduce odors at land application sites
include:
• Properly stabilize, condition and manage
biosolids at the treatment works to
minimize odors from the final product.
• Select remote sites and fields away from
neighbors (USEPA & USDA,2000).
• Clean tanks, trucks, and equipment daily.
• Whenever possible, subsurface inject or
incorporate biosolids into the soil (WEF
1997).
• Minimize the length of time biosolids are
stored (USEPA & USDA,2000).
Reduce visibility and maximize the distance
of the storage area from occupied dwellings
(USEPA & USDA,2000).
Avoid land application when wind
conditions favor transport of odors to
residential areas (USEPA & USDA,2000).
Plan field storage of biosolids based on the
stability, quantity, and length of time
biosolids are stored in addition to the
location of the site with respect to nearness
to neighbors and the meteorological
conditions (USEPA & USDA,2000).
• Avoid land application when nearby
residential areas are planning outdoor
activities or around holidays such as
Memorial Day, Independence Day, and
Labor Day WEF 1997).
• Develop an odor control plan and train all
staff to identify and mitigate odors.
Have alternate management including land-
filling for particularly malodorous batches
of biosolids.
Process Management
The degree of odor control necessary for biosolids
processing facilities is determined by site-specific
criteria such as:
The current and future proximity of a site to
residential or commercial developments.
• Local wind patterns, air mixing and
dispersion (air stability) factors.
Apply well stabilized material.
Temperature and humidity.
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The variability of the above factors on a
daily and seasonal basis.
off-site odors as the criteria for violation of
nuisance standards.
The amount of biosolids being processed. Sources of Odor
A computerized air dispersion model that addresses
magnitude, frequency, and duration of events, and
is calibrated and verified with on-site monitoring,
can be an effective tool to predict the impact of
odor emissions. This type of model may determine
how much and what type of control will be
necessary to prevent or minimize the impact. To
accomplish this task with some certainty of success,
a formal odor study should be commissioned.
During the planning or preliminary design of a
proposed biosolids processing facility, an odor
study should be conducted in light of the knowledge
and experience gained from successful operations
at similar facilities. For existing facilities that have
nuisance odor problems, the study should determine
the degree to which specific unit processes or area
sources contribute to the offsite impact. A detailed
sampling and monitoring program should be
conducted to determine a not-to-exceed nuisance
odor level. Liquid and gas samples can be
chemically analyzed for specific odor compounds.
Both direct sensory measurements of odor intensity
and odor strength are also useful to identify the
sources of the complex mixture of odor compounds
typically responsible for nuisance complaints.
Direct sensory measurements are conducted by a
panel of trained observers (expert noses) which
analyzes and rates air samples in terms of odor
intensity (n-butanol scale) and odor strength
(dilution to threshold or D/T scale.) A
comprehensive odor study should result in a full
understanding of the source and nature of the odor
emissions, identify available methods of odor
control, and establish criteria to measure the
effectiveness of the control technology.
Local ordinances may establish the degree of odor
control required. Generally, the ordinances are
written to prevent nuisance conditions at and
beyond the facility property lines. Numerical limits
of allowable concentrations of odorous compounds
are specified in some localities, while others specify
the frequency and/or duration of the detection of
Wastewater collection systems with long detention
times can result in septic conditions throughout the
wastewater treatment plant and subsequent odor
problems in biosolids handling and end use.
Aerated static pile, windrow and in-vessel
composting processes can produce objectionable
odors if anaerobic conditions occur and even with
aerobic conditions. Ventilation of air through the
compost material helps to control composting
temperature, maintain aerobic conditions, and
provide a means to direct the exhaust air stream
into an odor control device. The alkaline
pasteurization process produces ammonia as well as
other odor-causing compounds. Large scale
facilities are often enclosed and ventilated to a wet
chemical scrubber. Heat drying facilities usually
use wet scrubbers and/or afterburners such as
regenerative thermal oxidizers.
Biosolids processing facilities can be operated and
managed to reduce odor generation and emissions.
The quantity and intensity of odorous compounds
can be reduced by:
Operation and maintenance procedures to
prevent anaerobic conditions.
• Addition of oxidizing agents to prevent
formation of hydrogen sulfide.
Selection of polymers which are resistant to
breakdown at high temperatures and pH.
• Optimizing all stabilization processes such
as anaerobic digestion, aerobic digestion, or
alkaline stabilization.
• Evaluate the impacts of blending different
types of solids and storage. (Hentz and
Cassel)
• Scrubbing with a properly operated
chemical scrubber or biofilter.
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Addressing O&M optimization may result in dual
benefits. First, it will reduce the amount and
intensity of odors generated at the site, minimizing
costs of odor control equipment. Second, it will
generate a less odorous product, which will be
easier to store, transport, utilize, or market.
OVERVIEW OF ALTERNATIVES
Current Status
Current methods to control odors from biosolids
production facilities include biofilters, activated
sludge basins, wet chemical scrubbers, regenerative
thermal oxidizers, and odor counteractant or
neutralizing agents. The method chosen should be
based on the results of an odor audit and the type of
odor causing compounds present.
Biofilters- Description
Biofilters remove odors from a foul air stream by
the adsorption and absorption of odor causing
compounds onto a natural media bed where
microorganisms oxidize the compounds. The
indigenous bacteria and other microorganisms of
the media acclimate to the compounds present and
are sufficient to provide the "scrubbing" action; no
bacterial innoculation or chemical addition is
required. Biofilters commonly are used to treat the
air from all types of composting operations.
Biofilters-Advantages and Disadvantages
Advantages
Biofilters provide significant reduction of overall
odor emissions including Volatile Organic Carbon
emissions. It is a simple technology with minimum
moving parts and low energy requirements. Cold
winter temperatures do not affect biofilter
performance. Biofilters have a low profile and are
not as visible to neighbors as a system requiring a
stack. All the above advantages are true if biofilters
are properly sized, kept moist, and renewed
periodically.
Disadvantages
A major limitation of biofilters is the large land area
required for installations. The size of the biofilter
surface area is directly related to the airflow to be
treated and the need to provide about a 45 to 60
second detention time. Poor biofilter performance
is usually attributed to lack of moisture in the filter
media. Other performance inhibitors are short-
circuiting, pH depression, and high temperatures.
A concentration of ammonia greater than 3 5 ppm in
the foul air stream may cause a toxic accumulation
of ammonium in the media, leading to reduced
ammonia removal efficiency. The need to keep the
biofilters moist results in a significant amount of
water usage and the need to treat or dispose of
leachate and condensate. Design criteria are not
well established and biofilters may not be
appropriate for very strong odors.
Biofilters -Design Criteria
The medium is a mixture of materials that may
include bark, wood chips, yard waste or agricultural
waste compost, peat moss, sand, pulverized
volcanic rock, or oyster shells.
Oyster shells, or similar materials, can provide pH
control within the media. (Haines et al). Rock, sand
and bark are necessary to provide and maintain
porosity of the bed. The medium may be kept
moist by spray nozzles in the foul air collection
system and at the top of the biofilter
surf ace. (Haines et al).
Sometimes, water is also added inside the filter
through drip piping. The media bed is placed over
an air distribution system consisting of perforated
piping installed within a bed of gravel. An
impermeable membrane, such as a HDPE or PVC
liner, is placed under the gravel to facilitate leachate
collection and disposal. The biofilter can be
constructed within a compacted soil trench or
between soil berms. If the biofilter is installed
within a concrete, masonry, plastic or similar
container, the container must be designed to prevent
short-circuiting at the side walls and to resist
corrosion from the acidic leachate.
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The size of the biofilter is determined by the airflow
to be treated. The accepted loading rate of a
biofilter is 3 to 4 cfm per square foot of media bed,
with a media bed depth of 3 to 4 feet. Design
should provide for ease of removal because
biannual replacement or replenishment of the media
may be required. Periodic mixing or turning of the
media may be required to maintain the design air
flow and head loss through the odor control
ventilation system.
Biofilters are widely regarded as an effective, low
cost method of treating low to moderate odorous
air. A well operated and maintained biofilter can
reduce odors by 95% or greater (Schiffman et al)
(Boyette and Bergstedt). In some cases, biofilters
have resulted in the elimination of odor complaints.
(Alix). In other cases, improved composting
operations and biofilter renovation combined
resulted in a reduction of odor complaints. (Haines
et al).
Biofilters -Operation and Maintenance
It is important that biofilters be kept moist so that
the microbial community remains healthy and
effective. The goal is to operate the biofilters as
close to 100 percent humidity as possible. It is also
important to keep sufficient void space and avoid
air channeling, which results in short circuiting the
media. Large amounts of dust and particulate
matter in the foul air will build up in the biofilter
media and shorten the replacement time. In
addition, back pressure on the blowers will increase
maintenance requirements. An appropriate
temperature range must be maintained to keep the
microbial organisms healthy and functioning. High
temperature air (130-140 deg F) from composting
processes contains high concentrations of ammonia
that may be toxic to microorganisms. A typical
biofilter life expectancy is one to seven years with
biofilter replacement every two years. Operators
should develop a biofilter performance monitoring
protocol for routine assessment of odor control
efficiency.
Activated Sludge Basins -Description
Similar to biofilters, the activated sludge basins
used for secondary treatment at municipal
wastewater treatment plants can provide odor
removal by adsorption, absorption, condensation
and microbial oxidation.
Activated Sludge Basins -Advantages and
Disadvantages
Advantages
This can be a very cost effective alternative for
facilities which operate aeration basins. (Bowker)
Costs are usually lower for both capital and
operating expenses. Systems have been in
operation for over 40 years, and more than 25
facilities have used this technology. This system is
effective in treating moderate to high strength
odors. Activated-sludge basins are simple, with
low operation and maintenance considerations
(WEF MOP 24).
Disadvantages
Concerns about blower corrosion have been the
major impediment to use of activated sludge basins.
However, steel inlet filters and piping are more
common points of corrosion. There are reports of
accumulation of a tar-like substance or greasy film
on the internal components of blowers, and the
volume of foul air to be treated may exceed the
demand of the aeration tanks. The method may not
be appropriate for very strong odors.(WEF MOP
24)
Design Criteria - Activated Sludge Basins
The foul air is ventilated through a dedicated
blower and diffuser system or through the process
air distribution system. The foul air diffuser should
be submerged at least eight feet to achieve high
odor removal efficiency. The blower and diffuser
equipment must be designed to withstand the
corrosive nature of the air stream. Use of stainless
steel, PVC, and moisture traps will minimize
corrosion. The foul air volume can be minimized
by using flat gasketed covers on tanks or individual
enclosures for dewatering or blending equipment.
Inlet covers will prevent particulate accumulation in
fine bubble diffusers. Deep bed nitrification
biotowers are also used for odor control.(Lutz et al)
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Operation and Maintenance - Activated Sludge
Basins
If a diffused aeration system already exists, little or
no increase in O&M costs should be expected. The
blowers and air filters must be cleaned periodically
and the system monitored for odor causing
compounds.
Wet Chemical Scrubbers
Wet Scrubbers are best suited to treating high
intensity odor emission and large air volumes.
They are usually used at alkaline stabilization
facilities, biosolids drying facilities and
incinerators. There are several types of wet
scrubbers, the most commonly used in biosolids
facilities include packed bed, mist, and venturi
scrubbers. All are designed to maximize the
contact between the odorous compounds of the foul
air stream and a "scrubbing" chemical solution.
The compounds are absorbed and then oxidized by
the chemicals. The performance of a wet scrubbing
system depends on the solubility of the odors in the
scrubbing solution. This should be determined by
testing or from previous installations.(Heller and
Heller) Multiple stage systems, using water or
acid in the first stage to remove the ammonia,
followed by a chlorine or caustic and chlorine in the
second stage to remove sulfur based compounds,
are used to treat composting odors and more
commonly the ventilated air from alkaline
pasteurization facilities.
Advantages and Disadvantages - Wet Chemical
Scrubbers
Advantages
A two or three stage scrubber system can remove a
wide variety of odor-causing compounds. The units
have proven to have variable chemical consumption
and to be effective and reliable.
Disadvantages
There is a potential for emission of chlorinated
compounds and particulate from the scrubber
exhaust stack, as well as a potential for emission of
a bleach odor if chemical feed is not properly
controlled. Chemicals, power, and maintenance can
be expensive, and large amounts of water are
needed. The spent chemical must be properly
disposed, and softening is required for the water.
Design Criteria - Wet Scrubbers
The three most common types of wet scrubbers are
packed bed scrubbers, mist scrubbers and venturi
scrubbers.
Packed beds use a shower of scrubbing liquid over
a bed of high-surface-area plastic media to promote
droplet and film contact within a reaction chamber.
The foul air is ventilated through the plastic media
in a direction that is co-current or counter-current to
the liquid flow. The advantage of a packed
scrubber is that the concentration of the scrubbing
solution can be varied in response to fluctuating
odor levels. These units are usually the least costly
method of treating high intensity odors at
dewatering and storage facilities. Mist scrubbers
use compressed air to atomize a stream of
scrubbing liquid and a controlled ventilation pattern
within the reaction chamber to promote contact
without the use of media. Advantages of mist
scrubbers include a lower water usage and the
ability to handle a wide range of flow rates. The
disadvantages of mist scrubbers are O&M costs of
the air compressor, larger space requirements, and
the small clearances on the spray nozzles require
water softening and occasional acid washes (Heller
and Heller). Venturi scrubbers are similar in
operation to mist scrubbers, but atomize a
high-pressure stream of scrubbing liquid without
compressed air. The type of scrubbing liquid used
depends on the odor compounds to be treated. A
combination of sodium hydroxide and sodium
hypochlorite is effective for sulfide odors, while
dilute sulfuric acid is effective for ammonia odors.
Effective cooling of the scrubber gasses is also
needed for ammonia removal (Horst et al, 1991).
Operation and Maintenance - Wet Chemical
Scrubbers
Wet scrubbers require pumps, compressors, valves,
and instrumentation. As a result, operation and
maintenance costs are significant. Occasional
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maintenance and calibration is required for the
chemical supply system, liquid distribution nozzles
and ORP (oxidation reduction potential) and pH
probes. System maintenance can normally be
performed without interrupting the treatment.
However, mist scrubbers may require slightly more
nozzle maintenance because of the use of finer
spray nozzles.
Variable odor concentrations and constituents in the
process air will make scrubber operations difficult
and reduce effectiveness. Composting operations
have found that improving compost operations,
specifically mixing and uniform aeration, results in
less variability in dimethyl disulfide concentrations
in the scrubber feed air. Fewer and smaller
operating adjustments are required to maintain
optimum scrubbing conditions. (Murray et al, 1991)
Regenerative Thermal Oxidizers (RTO's)
RTOs use a high temperature to incinerate airborne
compounds in a short residence time combustion
chamber. This technology is usually used for
biosolids heat dryers, incinerators, or evacuation air
from biosolids storage tanks.
Advantages and Disadvantages - RTO's
Advantages
RTOs typically are used for VOC emission control,
with odor removal being incidental. This
equipment is compact compared to the area needed
for wet scrubbers or biofilters. They are well suited
to treating low volume, high strength air streams.
RTO's are more energy efficient than conventional
afterburners requiring only 10 to 20 percent of the
energy. Thermal efficeincies are often 90 to 95%
and the use of digester gas can reduce fuel costs.
Disadvantages
There are relatively few applications of RTOs
specifically for the control of biosolids processing
odors. Operators report these units are a significant
fuel cost. The system is only economical for high-
strength, difficult-to-treat air streams.
Design Criteria - RTO's
The required temperature in the combustion
chamber is 1,350 to 1,600 degrees F with a
detention time in the range of 0.3 to 3 seconds. It is
also important to configure the system to provide
sufficient turbulence and oxygen for efficient
combustion. (Heller and Heller, 1999) The RTO
may be fueled with fuel oil or natural gas, and heat
exchangers recover much of the exhaust gas heat to
preheat the incoming air.
Operation and Maintenance - RTO's
RTO's are an expensive odor control technology to
operate and maintain. High temperatures result in
significant fuel costs and frequent maintenance
and/or replacement of instrumentation.
Counteractants, Neutralizing Agents and
Oxidizang Agents
These products are used to reduce the impact of
odors from area sources, such as biosolids curing or
storage piles and point sources such as ventilation
exhaust stacks. Essential oils and proprietary
compounds are used as odor masking agents and as
odor neutralizing or counteracting agents. These
materials generally are non-toxic and
non-hazardous to humans and the environment.
They may be dispersed as a fine mist into the air at
processing facilities or added to the liquid waste
streams.
Oxidizing agents released into the wastewater react
with odor causing compounds to form a more
stable, odor free compound.
Advantages and Disadvantages -
Counteractants, Neutralizing Agents and
Oxidizing Agents
Advantages
The use of Counteractants and neutralizing agents
can be initiated quickly at a low capital cost. The
use of oxidizing agents, or Counteractants, in the
waste stream can greatly reduce odors in the
workplaces especially around thickening and
dewatering equipment. At some facilities the
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addition of potassium permanganate, an oxidizing
agent, temporarily reduces odors in the biosolids
product, (Pi sarczyk and Rossi) thereby making land
application less objectionable to a farmer's
neighbors. Some plants also observe improved
dewatering when using potassium permanganate.
Disadvantages
It is possible that the perfume-like odor from some
neutralizing agents may be perceived as an
objectionable or nuisance odor. The effectiveness
of neutralizing agents are limited to the area in
which they can be dispersed. Oxidizing agents can
act as a bactericides and inhibit biological
processes. The presence of non-odorous substances
that react with the oxidizer, will greatly increase the
cost of treatment.(WEF) Oxidizing agents are not
always effective and are sometimes expensive. The
system has a poor database and limited information
on odor removal efficiency.
Design Criteria - Counteractant, Neutralizing
Agents and Oxidants
Essential oils and proprietary compounds are
dispersed into the foul air stream as a vapor or fine
mist. Either a reaction chamber is provided to
maintain a contact and residence time or the
ventilation ductwork or exhaust tower is used to
apply the agent. Some products are claimed to
polymerize and precipitate odor molecules from the
air stream. The neutralizing agents are sometimes
sprayed continuously in the vicinity of odorous
tanks, truck loading or storage areas.
Another design uses oxidizing agents such as
chlorine, hypochlorite, chlorine dioxide, hydrogen
peroxide or potassium permanganate to prevent
septic conditions and the resultant hydrogen sulfide
odors. A small amount of oxidant is blended with
wastewater or liquid wastewater solids. A
potassium permanganate dose of 0.3% can reduce
the Threshold Odor Number from 1500 to 200. The
required dosage is dependent on pH. Less
potassium permanganate is needed at pH 5 or 7 than
at pH 9 (Pisarczyk. and Rossi, 1992).
Operation and Maintenance - Counteractants,
Neutralizing Agents and Oxidizing Agents
Once the proper dosage is determined, operation
and maintenance is relatively simple. Routine
maintenance of pumps, spray nozzles and
automated systems is required.
PERFORMANCE
The following table shows removal efficiency for a
variety of odor control technologies. Within the
past 5 years, the design and operation of biofilters
has been optimized and is now better understood
than ever. Most work on biofilter is for use at
composting facilities but due to their low cost, they
are also being examined for heat drying facilities.
TABLE 1 REPORTED REMOVAL
EFFICIENCIES
System
Biofilter
Activated Sludge
(coarse bubble)
Activated Sludge
(Fine Bubble)
H2S
> 98%
< 85% -
92%
> 99.5%
NH3
> 80%
> 90%
N/A
Odor
Units
(D/T)
> 95%
90 - 95%
> 99.5%
Wet Scrubbers
RTO
Chemical
oxidants
Counteractants
and neutralizing
agents
> 95%
N/A
>99%<
30%
> 95%
N/A
N/A
30%
< 80%-
99%
> 95%
up to 99%
N/A
1Hydrogen sulfide concentration measured above the
conveyor leaving the centrifuge.
Source: Schiffman et.al, Williams, Ostojic & O'Brien,
Giggey et al, Solomon, LeBeau & Milligan, Pisotti,
Singleton et al; Vaith et al; Ficek.
As with any odor control equipment, removal
efficiency is only one aspect of effectiveness. Odor
modeling will identify odor receptors and determine
the likelihood of odors being detected off site.
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TABLE 2 RELATIVE COSTS OF ODOR CONTROL TECHNOLOGIES
System
Biofilter
Activated
Sludge Basins
Overall
Moderate
Low, if
existing
system
Capital
Moderate-
but land
area
needed
Low, if
existing
system
Operation/
Maintenance
Moderate
Low, if existing
system, may
corrode blowers
Electrical or
fuel
Low
Low , if existing
system and
biosolids
processing
facility is close
Supplies/
Chemicals
Water needed
Low
Effectiveness
High>95% in
compost
High 90-95% for
H2S and
Ammonia
Wet Chemical
Scrubbers
Regenerative
Thermal
Oxydizers
Oxidizing
Agents
Counteractant
& Neutralizing
Agents
High
High
Varies-
moderate
to high
Moderate
High-up to
50% of
total plant
costs
Moderate
Low
Low-
moderate
High - much
high speed
equipment +
instrumentat'n
High- due to
high temp
equipment
Low- just mat'l
handling issues
Varies from one
plant to another
High - must
move water at
high pressure
High-
tremendous
heat demand
Low -small
pumps required
Low
High - chemical
costs and water
demand
High - oil or gas
High - potassium
permanaganate
can be expensive
High - usually
patented
compounds
High <80%-99%
handles alkaline
stab and all plant
odors
Good for organic
odorants from
incinerators, and
heat dryers
Varies from one
plant to another
Varies, but may
help at end use
site.
Source: Hentz et al, Haines et al, Giggey, Ostojic and O'Brien, Pisarczyk and Rossi, Ponte, Bowker, Vaith et al, Wlliams,
Wu.
COSTS
Costs for odor control will vary significantly from
one location to another and from one technology to
another. At the Hoosac Water Quality District
(HWQD) composting facility the biofilter was less
than 3% of the capital cost and media replacement
was about 7% of O&M costs (Alix,1998) .
Multistage wet scrubbers and RTO's can result in
30 to 50% of capital and operating costs of a
biosolids processing facility. Potassium
permanganate costs $1M per year at a facility that
dewaters and incinerates 60 dry tons per day
(DTPD) which equates to $45 per dry ton.
The following table compares the cost factors for
each technology. In addition, biosolids processing
facilities should budget funds to conduct a facility
wide odor audit, use odor modeling whenever
possible, avoid septic conditions in wastewater and
solids, evaluate polymers and liquid blending and
storage practices, maintain records of odor
complaints and conditions, and incorporate
language in land application contracts to assure best
management practices.
REFERENCES
Other Related Fact Sheets
Alkaline Stabilization of Biosolids
EPA 832-F-00-052
September 2000
In-Vessel Composting
EPA 832-F-00-061
September 2000
Land Application of Biosolids
EPA 832-F-00-064
September 2000
-------
Centrifugal Dewatering and Thickening 7.
EPA 832-F-00-053
September 2000
Filter Belt Press Dewatering
EPA 832-F-00-057
September 2000 8.
Recessed Plate Filter Press Dewatering
EPA 832-F-00-058
September 2000
Other EPA Fact Sheets can be found at the
following web address:
http://www.epa.gov/owmitnet/mtbfact.htm 9.
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ADDITIONAL INFORMATION
Post Buckley Schuh & Jernigan, Inc.
Larry Hentz, V.P. Wastewater Program Manager
One Town Center, Suite 302
4201 North View Drive
Bowie, MD 20716
National Biosolids Partnership
Peter S. Machno, Ph.D.
601 Wythe Street
Alexandria, VA 22313
Steve T, Welch
Assistant Executive to the Director
University Area Joint Authority
1576 Spring Valley Road
State College, PA 16801
U.S. EPA,
John Walker
Mail Code 4204
401 M St., S.W.
Washington, DC 20460
City of Los Angeles
Ray Kearney
12000 Vista Del Mar
Playa Del Rey, CA 90293
For more information contact:
Municipal Technology Branch
U.S. EPA
Mail Code 4204
1200 Pennsylvania Avenue, NW
Washington, D.C. 20460
sMTB
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