Capability
Profile
Odor Control With ProSweet*
Introduction
Driven by changes in the Clean Air Act Amendment
(CAAA), the requirement for improved odor control
may exist in many industrial facilities. Under this act,
regulatory bodies will be forcing industrial plants
such as paper mills, refineries and food processors
to improve the quality of air they are emitting. This
legislation is aimed at reducing toxic chemical emissions. Odor control has come into focus.
fensive and toxic odors. With this in mind, GE’s
Water & Process Technologies has developed a
treatment program which offers a solution to this
industrial need in an easy to apply and economical manner. It is this technology which affords GE
a definite competitive advantage in this area.
Odor Control in the Industrial Market
Place
Odors emitted from manufacturing facilities can
impact an operation in many ways:
Potential for odor control technologies exists in
many industries:


Pulp & Paper Mills

Oil Refineries/Hydrocarbon Processing Industries (HPI)

Foundries/Steel Mills/Automotive Plants

Food Processing Facilities

Textile Mills

Other Industrial Manufacturing Markets
Public complaints about odor can negatively
affect an industry’s image in the marketplace
and its ability to carry out an effective public relations policy with the surrounding community.

Safety concerns can arise from people working
in areas where odors can overcome them.

Productivity impact can be seen in areas of a
facility where objectionable odors exist due to
employee avoidance or neglect.

Production can be affected through the presence of odors and odor producing conditions
which taint product quality.

Equipment integrity can be threatened by the
presence of many odors which are corrosive in
nature.
It should be noted that not all manufacturing facilities produce odors or experience these problems,
nor are all odors noxious or toxic in nature. However, one very large segment of the odor control market which does fit this description and dictates
immediate and complete attention is the control of
hydrogen sulfide (H2S) generation and evolution.
Although the CAAA does not explicitly regulate hydrogen sulfide, it does call for the elimination of of-
The use of chemicals as a method of odor control
is regarded as an acceptable treatment option
because of the minimal amount of capital investment required. Other acceptable technologies,
including combustion, oxidation, and stripping are
also very efficient but require considerable capital
equipment investment. In many of the industrial
applications mentioned above such as paper
making, oil refining and steel, odor control methods such as incineration, carbon adsorption, wet
scrubbing, electrostatic precipitation, source modification, and odor masking may be found. In hospitals, office buildings and schools, other methods
such as filtration and absorption are used. Many
industrial facilities, however, find it is more cost
effective to implement and operate a chemical
Find a contact near you by visiting www.ge.com/water and clicking on “Contact Us”.
* Trademark of General Electric Company; may be registered in one or more countries.
©2011, General Electric Company. All rights reserved.
cp81.doc Aug-11
based odor control program than to incur up front
equipment purchases.
A chemical program is a direct benefit to those who
have to put in place an odor control program now,
with a low cost impact on their bottom line. With
odor control programs involving equipment purchases, the time lapse between purchase and startup may involve months, consuming valuable time
and becoming costly in fines and neighbor complaints.
Background
H2S is the most commonly known and prevalent
odorous gas associated with wastewater treatment
systems. It has a characteristic rotten egg odor, is
extremely toxic, and is corrosive to metals.
Figure 1a: Effect of pH on hydrogen sulfide equilibrium
Process and waste streams, in which the direct introduction of sulfides occurs, are likely candidates
for odor problems.
In addition to direct process sources of reduced sulfur compounds, the other primary contributor of
hydrogen sulfide odors from wastewater streams is
the biochemical reduction of inorganic sulfur compounds.
Under anaerobic conditions, sulfate reducing bacteria use sulfate as an oxygen source to metabolize
organics in the waste stream:
SO4= + 2C + H2O → 2 HCO3- + H2S
Most sulfate reduction occurs within a biological
slime layer which protects the sulfate reducers from
oxygen present within the bulk waste stream itself.
The rate at which hydrogen sulfide is generated is
dependent upon the concentration of sulfate and
organics in the waste stream, the level of dissolved
oxygen, pH, temperature, and the velocity of the
water.
The conditions leading to H2S formation generally
favor the production of other malodorous organic
compounds such as mercaptans, thiophenol, and
thiocresol. Investigations of the conditions favoring
H2S formation can also help to quantify the potential
for odor generation from other compounds. Thus,
solving H2S odor problems can often solve other
odor problems as well.
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Figure 1b: Proportions of H2S and HS- in dissolved sulfide.
H2S dissolves in water and dissociates according
to the following reactions:
H2S ↔ HS- + H+
HS- ↔ S= + H+
Figures 1a and 1b show the distribution of sulfide
species as a function of pH. The relative H2S concentration increases with decreasing pH. At a pH
of 7.0, H2S represents 50% of the dissolved sulfides present, while at a pH of 6.0, over 90 percent
of the dissolved sulfides is in the form of H2S. If
part of the dissolved H2S escapes to the atmosphere, the remaining dissolved sulfide will be divided between H2S and HS- in the same proportion
as before because the equilibrium re-establishes
itself almost instantly.
Capability Profile

100 ppm (mg/L): IDLH (Immediately Dangerous
to Life and Health)
Very low concentrations of this gas can cause serious health hazards. Death has resulted from
concentrations of 300 ppm (mg/L) by volume in
air. Such concentrations can be obtained in an
enclosed chamber with high turbulence, from
wastewater containing 2 ppm (mg/L) of dissolved
sulfide at a pH of 7.0.
Based on Henry’s Law, Figure 2 was developed to
show H2S levels in the atmosphere (closed vessel)
in equilibrium with the given concentrations of H2S
in the water at the respective wastewater temperatures.
Preliminary Monitoring Program
Figure 2: Equilibrium concentration of H2S in air
The distinction between the types of sulfide compounds is significant because only the H2S can escape from solution and create odor, corrosion, and
health problems. It is important, therefore, to quantify the total and dissolved sulfides present and the
pH of the wastewater.
Health Effects of H2S
H2S is an acutely toxic gas. H2S is heavier than air, is
colorless and has a characteristic rotten egg smell
at low concentrations. But as the levels of H2S increase, we become generally unaware of its presence. A person’s ability to sense dangerous
concentrations by smell is quickly lost. If the concentration is high enough, unconsciousness will occur
suddenly, followed by death if there is not a prompt
rescue.
The following outlines the current exposure limits for
hydrogen sulfide as set by NIOSH (National Institute
for Occupational Safety and Health) and ACGIH
(American Conference of Government and Industrial
Hygienists).

1 ppm (mg/L): TLV/TWA (8 hour maximum average exposure)

5 ppm (mg/L): STEL (Short Term Exposure Limit)

10 ppm (mg/L): Ceiling Recommended Exposure
Limit
Capability Profile
Normally, repeated odor complaints are the first
indicators of potentially damaging sulfide generation within a system. In more extreme cases, the
problems are manifested by deteriorated conditions in pipes and electrical equipment or by
structural failures.
Evidence of sulfide generation warrants the implementation of a preliminary program to assess
the overall potential for sulfide generation. Such a
preliminary program should include a thorough
investigation of odor complaints, and a systematic
investigation of the wastewater collection and
treatment system to identify major potential contributors.
Preliminary Sampling
The survey of odor generation should begin at the
waste treatment plant and proceed upstream
throughout the facility. The preliminary survey
should consist of a simplified field analysis of sulfide levels in the water and air to determine the
actual trouble areas. Hand held monitors can be
used for air sampling. Test kits such as those supplied by Chemetrics can be used for wastewater
testing. Normally, odor problems will occur when
dissolved sulfide levels are 1.0 to 1.5 ppm (mg/L)
or greater.
The following locations should be checked:
1. Lift stations - sample wet-well influents, pump
discharges, and ends of pressure mains to determine sulfide balance.
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2. Gravity sewers - turbulence may release H2S gas
and cause corrosion of manhole chambers.
3. Sludge holding tanks - residual H2S and anaerobic activity will cause problems.
4. Areas of turbulence and long detention times sample locations of turbulence where sulfide
may be released. Measurement of total sulfides
before and after the point of turbulence can give
an indication of the quantity of H2S released to
the atmosphere.
Recycle streams from thickeners, digesters, and
other sludge treatment processes should also be
sampled, as these can contain high concentrations
of H2S that can result in severe odor and/or corrosion problems at the point of side stream return. Air
samples from enclosed spaces exposed to
wastewater may also be tested to determine the
severity of odors.
Wastewater characterization
The wastewater should be analyzed for the following:
1. Sulfates (SO4=), ppm (mg/L)
2. pH
3. Total Sulfides (TS), ppm (mg/L)
4. Biochemical Oxygen Demand (BOD5), ppm
(mg/L)
5. Dissolved Oxygen (DO), ppm (mg/L)
ProSweet Solution
The current family of ProSweet products includes
three distinct categories of technology:

Organic Scavenger

Biomodifier

Counteractant (Odor neutralizer)
Organic Scavenger - The organic scavengers are
comprised of a unique proprietary technology
(non-amine based) and the traditional cyclic
amines.
ProSweet organic scavengers will selectively react
with any reduced sulfur compounds that have
acidic protons. Therefore, many malodorous sulfur
odors can be treated successfully with these
products.
Proper treatment levels for ProSweet scavengers
depend on many factors such as stream flow rate,
temperature, H2S concentration, desired H2S removal efficiency, and pH. Assessment of these
factors will aid the GE sales representative in recommending treatment rates, control procedures,
and specific application points.
Dosages are often controlled based on actual operating conditions and the degree of scavenging
required. It may not be necessary to scavenge all
malodorous sulfides. Treatment levels will be dictated by perception and/or satisfactory monitoring levels.
Chemical Treatment
The selection of single or multiple feed-points is
site specific. Sulfide containing streams should be
identified, in addition to locations, with high H2S
concentrations in the air. The feed point should be
located at the generation point or upstream of the
affected areas. ProSweet products can be fed with
a standard metering pump to various locations
such as full flowing pipelines, open channels,
sludge lines, or sludge holding tanks.
Numerous chemicals have been employed for control of sulfides in wastewater collection systems.
The benefits of using a ProSweet non-amine
based organic scavenger includes:
Chemical addition can control sulfides by:

A selective activity with reduced sulfur compounds
2. Chemical oxidation (Cl2,H2O2)

No pH change
3. Precipitation (Metal salts)

Wide pH range of applicability
4. pH control

No sludge generation.
6. Temperature, °C/°F
7. Suspended Solids (TSS), ppm (mg/L)
In addition to these water analyses, H2S levels in the
ambient air should also be determined with an appropriate air monitor.
1. ProSweet Solution
Page 4
Capability Profile

Easy to handle and feed
Chemical Oxidation

No adverse effect on biological wastewater system
Chlorine donating materials are rarely used because of their safety and handling problems and
the probability of THM formation.
Biomodifiers - Nitrate has long been used in facultative and anaerobic lagoons to control odors. Facultative and obligate anaerobic bacteria, which are
responsible for odor and sulfide production, prefer
nitrate (over sulfate) as an oxygen source when
available. When nitrate is present, these sulfide producing bacteria use this to the exclusion of sulfate.
This results in the production of nitrogen gas and
other nitrogenous compounds rather than sulfide.
In some cases, it is more appropriate to inhibit the
biological production of malodorous H2S from water
and wastewater streams with biomodifiers. ProSweet biomodifiers are a blend of a metabolic inhibitor to prevent the biological generation of
hydrogen sulfide and an organic scavenger; providing a dual functional product.
Proper treatment levels for this ProSweet technology depend on many factors such as stream flow
rate, temperature, pH and levels of biochemical oxygen demand (BOD5), sulfate and dissolved oxygen.
Assessment of these factors will aid the GE sales
representative in recommending treatment rates,
control procedures and specific application points
Counteractant - These are chemicals that interfere
with the malodor. The counteractant does not
chemically react with the malodor, but reduces the
perceived odor level by eliminating the objectionable characteristics of the malodor. The elimination
or neutralization of odor does not indicate in any
way that these chemicals have the ability to neutralize the health and safety effects the odor causing
agent may have.
This technology offers an effective way of dealing
with a wide variety of odor types, mostly nuisance
odors in oxidized form. This can also be used to control residual odors from sulfide treatment or odors
generated by sulfides only if the H2S air levels are
consistently below the safe exposure limits established by ACGIH and NIOSH.
In this type of application, the malodorous air
streams are treated with atomized or vaporized
ProSweet product. For solid waste applications, the
product may be sprayed on piles or landfills.
Hydrogen peroxide chemically oxidizes H2S according to the following reactions:
pH < 8.5: H2O2 + H2S S + 2H2O
pH > 8.5: 4H2O2 + S= SO4= + 2H2O
At pH < 8.5, the stoichiometric H2O2 requirement is
1g H2O2 /1g H2S. In practice, a greater weight ratio
may be required because hydrogen peroxide cannot selectively oxidize sulfides. The actual dosage
rate will be proportional to the concentration of
oxidizable compounds in the wastewater.
Metal Salts
The salts of many metals will react with dissolved
sulfide to form metallic sulfide precipitates, thus
preventing H2S release to the atmosphere. For effective removal of dissolved sulfides, the metallic
sulfide formed must be highly insoluble.
Iron salts have been used for sulfide control. The
ferrous ion reacts with sulfide as shown below.
Fe++ + HS- FeS + H+
Pomeroy found that the reaction of a mixture of
iron salts with a molecular ratio of one part ferrous to two parts ferric was superior for sulfide
control compared to the reaction of either one
alone. The reaction of the mixed iron salts was
hypothesized to occur as follows:
Fe++ + 2Fe+++ + 4HS- Fe3S4 + 4H+
Strong Alkalies
Increasing the system pH reduces the proportion
of dissolved H2S in the H2S and HS- equilibrium. For
example, at a pH of 7.0, equal concentrations of
dissolved H2S and HS- exist at equilibrium, while at
a pH of 8.0; only about 10% of the dissolved sulfide exists as H2S. Since dissolved H2S is the only
form which can be released to the atmosphere, it
follows that increasing the pH would reduce odors
and corrosion by maintaining the dissolved sulfides in the HS- and S-2 forms.
ProSweet Program Applications
In order to successfully apply the ProSweet odor
control products, intimate contact between H2S
Capability Profile
Page 5
and the products is necessary. During the system
survey it is critical to identify an appropriate feed
point for the treatment program. The survey will
help to pinpoint areas where the treatment program
can be set up for maximum effectiveness. In general, odor control products should be fed at the H2S
generation area or ahead of the highest concentration of H2S odor points. For example, feed ahead of
the clarifier if the odor is coming from the clarifier;
or, feed ahead of the inlet to the sludge holding tank
if the odor is highly concentrated in the holding
tank.
Figure 4: Paper Mill System Wastewater Treatment
The H2S meter and the Hach sulfide kit were used
to test for H2S in the air and water at selected
sites. The level of H2S in the filtrate water from the
twin belt filter presses was 10 ppm (mg/L) and, in
the surrounding air at the sludge holding tank
from the primary clarifier, it was 20 ppm (mg/L). A
feed point for ProSweet ahead of the sludge holding tank was the selected location to reduce the
concentration of H2S in the system.
Figure 3: Automotive Foundry Wastewater Treatment
As an example (Figure 3), in a large Midwestern automobile foundry wastewater system, there was no
H2S in the effluent of the clarifier. There was less
than 1 ppm (mg/L) of H2S in the water after the sand
filters effluent; 1 ppm (mg/L) after the carbon filters
and 12 ppm (mg/L) of H2S in the Parshall Flume pit.
The H2S meter was used for H2S determinations in
the air at these locations and only at the Parshall
Flume pit was there a significant accumulation of
H2S in the air. The accumulation of H2S at this location was 20 ppm (mg/L). At this level, H2S is quite
unpleasant and unsafe; workers usually try to avoid
the area until it is dissipated by opening doors, windows and operating exhaust fans. In this example, a
feed point ahead of the Parshall Flume was selected
as the desired location to eliminate the heavy concentrations of H2S.
In another example, at a large Midwestern paper
mill a survey of the physical equipment at the
sludge dewatering building was made (Figure 4).
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Figure 5: General Layout of waste treatment system at
newsprint mill
A newsprint mill was receiving complaints from
employees and the neighboring community because of H2S generation at their waste treatment
facility. The general layout of the waste treatment
system is shown in Figure 5. Waste plant influent
is split between two parallel primary clarifiers.
Overflow from the clarifiers enters an activated
sludge system. Biological solids are then removed
in the secondary clarifier prior to effluent discharge to the river. Secondary sludge is dewatered on a belt filter press, while mixed primary
and secondary sludge is dewatered in a screw
press.
Capability Profile
Air and water samples determined the source of
odor generation to be the sludge. Odors originated
both from the primary clarifier itself and the sludge
dewatering equipment. Ambient H2S levels between
50 and 150 ppm (mg/L) were measured at the primary clarifier outlet and the overflow lift station.
Around the sludge presses, H2S was measured between 25 to 50 ppm (mg/L) in the air.
Application Monitoring
The mill evaluated ferric sulfate addition to the
sludge ahead of the presses in an attempt to react
with the sulfide present. This approach provided little relief on odor generation. It was decided not to
inject iron salts into the primary clarifier inlet because of the risk of iron carryover into the aeration
basin. It was feared that the resulting precipitation
of phosphate would make nutrient control difficult
and aggravate an existing filamentous bulking
problem in the secondary clarifier.

pH meter

Chemets Sulfide Test Kit

Drager Tube Kit

H2S air monitor

Dissolved Oxygen meter

BioHealth Wastewater Test Kit
A proprietary non-amine based organic scavenger
was then applied to the influent of the primary clarifiers. In less than 24 hours, odors were under control
(Table 1). Over time, not only were the odors eliminated, but other impacts on system operation were
realized. The growth of filamentous bacteria in the
secondary clarifier was reduced, creating a faster
settling sludge. It was surmised that the elimination
of ionic sulfide from the water reduced the available
sulfur supply to the Thiothrix ssp. in the aeration basin. As a result, the need for chlorine and defoamer
addition to the clarifier because of the adverse effects of excessive growth of filamentous bacteria
was eliminated. Because of better quality solids,
polymer requirement for the belt press dewatering
declined by 20%.
Table 1: Ambient H2S Levels Before and After Organic
Scavenger Application.
Location
Before
Scavenger
After
Scavenger
Primary Clarifier
50 to 150 ppm
(mg/L)
2 to 3 ppm
(mg/L)
Primary Sludge
Press
25 to 50 ppm
(mg/L)
1 to 2 ppm
(mg/L)
Secondary
Sludge Press
25 to 50 ppm
(mg/L)
< 1 ppm
(mg/L)
Capability Profile
Besides your sense of smell, there are a few essential testing items you should consider when
scoping out for odor control treatment program or
servicing an existing one.
The following list should prepare you for the necessary testing.
The pH meter will allow you to determine the
amount of H2S available in the water stream that
can evolve. The Chemets kit is a convenient method to determine the total sulfide content in the
water stream. This can be used to determine the
initial ProSweet feed rate. When servicing an odor
control program, use a continuous air monitor to
measure the ambient H2S levels -- this method will
indicate the ultimate effectiveness of the program.
Use the Drager Tube Kit when running “bench
tests”. This is a good way to show the effectiveness of a product and to determine the initial feed
rate.
Use the Dissolved Oxygen meter to determine if
anaerobic conditions exist. Anaerobic conditions
can lead to biological sulfate reduction and production of H2S.
The BioHealth Test Kit is a technology based on
measurement of Adenosine Triphosphate (ATP).
This can be used to monitor anaerobic biological
activity, especially in situations where you would
not expect to have any aerobic biological activity.
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