Downloaded from CivilDigital.com
BY:dinesh
Downloaded from CivilDigital.com
Contents:
 Why do we need this
 Types of odors
 Source of odors
 Movement of odorous gases
 Strategies for odor control
 Odor control method
 Design of odor-control facilities
Why do we need odor
management??
Downloaded from CivilDigital.com
 The potential release of odors is a major concern of
public acceptance.
 For homo-sapiens odor is primarily related to the
psychological stress the odor cause.
 Higher concentration of odorous gases can be lethal.
 Projects have been rejected & some waste water
agencies have been subjected to fines and other legal
action over odor violation.
Types of odors
Downloaded from CivilDigital.com
 Most of odorous compound typically contain either
sulfur or nitrogen
 Rotten egg smell of hydrogen sulfide is the odor
encountered most commonly
ODOROUS COMPOUND
ODOR THRESHOLD
ppm
CHARACTERISTIC ODOR
Ammonia
46.8
Pungent, irritating
Methyl Amine
21.0
Putrid, fishy
Chlorine
0.314
Pungent, suffocating
Hydrogen sulfide
0.00047
Rotten egg
Downloaded from CivilDigital.com
Source of odor
1- Waste water collection
system:
 The biological conversion, under anaerobic condition
of O.M. containing nitrogen & sulfur
 Discharge of industrial W.W. that may contain
odorous compounds
 Odorous gases released to the sewer atmosphere can
accumulate & be released at air release valves,
cleanouts, manholes, house vents.
Downloaded from CivilDigital.com
Location
Source/ cause
Odor potential
Air release valves
Accumulation of odorous gases released
from waste water
High
Cleanouts
Accumulation of odorous gases released
from waste water
High
Access ports (man
holes)
Accumulation of odorous gases released
from waste water
High
Industrial waste
water discharges
Odorous compounds may be discharged
to water
Variable
Downloaded from CivilDigital.com
2- Waste
water treatment facilities:
 Head works & preliminary treatment
operations have the highest potential for
release of odor
 Side stream discharge including return
flows from filter backwashing and from
sludge processing facilities are often major
source of odor
Downloaded from CivilDigital.com
Location
Sources / causes
Odor potential
Headworks
Release odorous gases generated in waste water
collection system due to turbulence in
hydraulic channel and transfer points
High
Screening
facilities
Putrescible matter removed by screening
High
Preaeration
Release of odorous compounds generated in
waste water
High
Grit removal
Organic matter removed with grit
High
Side stream
returns
Return flows from bio solids processing
facilities
High
Primary clarifiers
Floating sludge, scum, turbulence in effluent
weir that release odor
Moderate
Aeration basin
High organic loading, poor mixing, inadequate
DO, solids deposit
Low/moderate
Secondry clarifier Floating solids, excessive solid retention
Low/ moderate
from CivilDigital.com
3-sludge and BiosolidsDownloaded
handling
facilities:
 Typically the most significant source of odor in a TP
are sludge thickening, anaerobic digesters and sludge
load-out facilities.
 Shearing of solids in mixing by dewatering causes odor
release
 Proteinaceous biopolymer are major mechanism once
released
 Trimethylamine above 9 pH is a gas a can be released
in air
Downloaded from CivilDigital.com
Location
Source/ cause
Odor
potential
Thickeners
Odor release by turbulence, solids deposits,
temperature increase
High/moderate
Aerobic
digestion
Incomplete mixing in reactor
Low/ moderate
Anaerobic
digestion
High sulfate contents in solids, leaking
hydrogen sulfide gas
Moderate/ high
Sludge storage
basin
Lack of mixing, formation of scum layer
Moderate/ high
Sludge loadout
facilities
Release of odor during the transfer of bio
solids
High
Alkaline
stabilization
Ammonia generation resulting from
reaction with lime
moderate
Downloaded from CivilDigital.com
Movement of odors
 Odorous gases hover over the point of generation
 They may be measured at great distances from point of
generation
 In the evening or early morning hours a cloud of odor
develop over the treatment plant unit, and then
transport(even 25 km) known as puff movement
 Puff movement of odors developed by Wilson(1975).
To reduce the effects we install barriers to induce
turbulence and/or use wind generators
Downloaded from CivilDigital.com
Strategies for Odor Management
 Control of odor causing W.W. discharge to collection





system
Odor control in W.W. Collection and treatment
Installation of Odor Containment and Treatment
measures
Chemical additions to W.W. for Odor control
Use of odor Masking and Neutralization
Use of Turbulence-inducing Structures and Facilities
Downloaded from CivilDigital.com
Control of discharge to W.W. collection system
 Requiring pretreatment of industrial wastewater
 Providing flow equalization at the source to eliminate
slug discharge of wastewater
 Adoption of more stringent waste discharge ordinance
and enforcement their requirements
Downloaded from CivilDigital.com
Downloaded from CivilDigital.com
Odor control in wastewater collection system
 Maintaining aerobic conditions by adding hydrogen




peroxide, pure oxygen or air
Controlling anaerobic microbial growth by
disinfection or PH control
Oxidizing odorous compounds by chemical addition
Design of W.W. collection system for mass turbulence
Off-gas treatment at selected locations
Downloaded from CivilDigital.com
Odor control in wastewater treatment facilities
 Design details to be considered to minimize release of
odor at treatment plants:
 Use of submerged inlets & weirs, elimination of
hydraulic jumps, elimination of physical conditions
leading to formation of turbulence, off-gas treatment
etc.
 Addition of chemicals such as: chlorine, hydrogen
peroxide, lime or ozone
Downloaded from CivilDigital.com









Design and operational changes include:
Minimization of free fall turbulence by controlling water
levels
Reduction of overloading of plant processes
Increasing the aeration rate
Reducing solids inventory and sludge backlog
Increasing the frequency of pumping of sludge & scum
Adding chlorinated dilution water to sludge thickeners
Increasing the frequency of disposal of grit and screenings
Cleaning odorous accumulations more frequently
Containment, ventilation, and treatment of odorous gases
Odor containment & treatment
measures
Downloaded from CivilDigital.com
 Installation of collection hoods and air handling
equipment for directing the gases to treatment units
 Typical containments alternatives are reported in the table
Facility (source)
Suggested control strategy
Wastewater sewers
Seal existing access ports. Eliminate the use
of structure that create turbulence
Bar racks
Cover existing units
Grit chamber
Cover the aerated grit chamber and in
conventional type reduce turbulance
Primary and secondary sedimentation tanks
Cover existing units, replace overflow weirs
with submerged weirs
Sludge thickener
Cover existing units
Chemical additions to W.W. for
Odor control
Downloaded from CivilDigital.com
 Odors can be eliminated in liquid phase by adding
chemicals to achievet
1) chemical oxidation 2) chemical precipition 3)pH control
 NaOCl, H2O2, KMnO4, O3 will oxidize H2S and other
odorous compounds.
 Ferrous chloride and ferrous sulfate can also be used for
odor control by precipitation of sulfide ion as ferrous
sulfide.
 By increasing the pH value of W.W. it results in decreased
bacterial activity and also shifts the equilibrium so that
sulfide ion is present as HS (-).
Use of odor Masking and
Neutralization
Downloaded from CivilDigital.com
 Sometimes, chemicals are used to mask an offensive
odor with a less offensive odor. Masking chemicals are
compounds having most common aromas.
 Neutralization involves finding chemicals compounds
which can be combined with the odorous gases in
vapour state so that combined gases cancel each
other`s odor and resulting in a gas with low odor
intensity
 Masking and neutralization are short term
management techniques.
Use of Turbulence-inducing
Structures and Facilities
 Physical facilities are used to induce atmospheric
turbulence to reduce gas phase odor turbulence.
 Odorous gases that develop under quiescent
conditions over the lagoons are diluted as they move
away from the storage lagoons, due to local turbulence
induced by the barriers.
Downloaded from CivilDigital.com
ODOR TREATMENT METHODS
 Treatments are used either to treat the odor producing
compounds in the waste water or to treat the foul air.
SOME PRINCIPAL METHODS: Chemical scrubbers
 Activated carbon absorbers
 Vapour phase biological treatment
 Thermal process
Downloaded from CivilDigital.com
Chemical scrubbers
 Design objective is to provide enough contact between
air, water and chemicals to enable oxidation and
entrainment of odorous compounds.
 Most commonly used scrubbing liquids are sodium
hypochlorite , potassium permanganate and hydrogen
peroxide solutions.
 Sodium hydroxide is also used in scrubbers where H2S
concentration is high in gas phase.
Simplified scrubbing reactions:
With sodium hypochlorite
H2S + 4NaOCl + 2NaOH ---- Na2SO4 + 2H2O + 4NaCl
H2S + NaOCl ---- S + NaCl + H2O
With potassium permanganate
3H2S + 2KMnO4 ---- 3S + 2KOH + 2MnO2 + 2H2O
3H2S + 8KMnO4 ---- 3K2SO4 + 2KOH+ 8MnO2 + 2H2O
With hydrogen peroxide
H2S + H2O2 ------- S + 2H2O
pH<8.5
Downloaded from CivilDigital.com
 Reaction products that can occur, depending on the
local waste water chemistry , include elemental sulfur,
sulfate thionates, dithionates, and manganese sulfide.
 Potassium permanganate is generally used in smaller
units as it is expensive.
 Hypochlorite scrubbers are expected to remove
oxidizable odorous gases when other gases
concentration is minimal.
 In case where the concentration of odorous
components in the exhaust gas from the scrubber are
above desired levels, multistage scrubbers are often
used.
Effectiveness of hypochlorite
wet
Downloaded
from CivilDigital.com
scrubbers for removal of several
odorous gases
Gas
Expected removal
efficiency, %
Hydrogen sulfide
98
Ammonia
98
Sulfur dioxide
95
Mercaptans
90
Other oxidizable compounds
70-90
Design consideration for chemical
scrubbers
Downloaded from CivilDigital.com
Item
Units
Value
Packing depth
m
1.8-3
Gas residence time in
Packing
s
1.3-2
Scrubbing liquid flow
rate
Kg H2O/kg airflow
1.5-2.5
pH
Unit less
11-12.5
Temperature
Degree centigrade
15-40`
Caustic usage
Kg NaOH/kg sulfide
2-3
Downloaded from CivilDigital.com
Downloaded from CivilDigital.com
Activated Carbon Adsorbers
 Rate of adsorption for different constituents or
compounds will depend on the nature of the
constituents (polar Vs. Non polar)
 Removal of odors also depends on the concentration of
the hydrocarbons in the odorous gas, as hydrocarbons
are removed preferentially before polar compounds.
 As carbon beds are limited and needs to be
regenerated thereby for prolonged life it is used in two
stages followed by wet scrubber
 For effective use of activated carbon the composition
of odorous gases to be removed must be known.
Downloaded from CivilDigital.com
Downloaded from CivilDigital.com
Vapor phase biological treatment
 Two principal biological processes used
for treatment of odorous gases present
in the vapor phase are
Bio filters
Conventional biological processes
Downloaded from CivilDigital.com
Bio filters
 As the odorous gases move through the packing in the
biofilter, two processes occur simultaneously
a) sorption (absorption/ adsorption)
b) bio-conversion
 Odorous gases are absorbed into the moist surface of
biofilm layer and the surface of bio filter packing
material
 Than microorganisms, principally bacteria,
actinomycetes and fungi oxidize the absorbed gases
and renew the treatment capacity of the packing
material.
Downloaded from CivilDigital.com
 Moisture content and temperature are important
environmental conditions and must be maintained to
optimize micro-organism activity
 Drawback being is they require large surface area to
operate
Design considerations for odorcontrol Bio-filters
Downloaded from CivilDigital.com
 The type and composition of the packing material
sufficient porosity and near uniform particle size
particle with large surface areas
ability to support large micro-flora population
 Facilities for gas distribution
perforated pipes
prefabricated under drain system
 Maintenance of moisture within the bio-filter
 Temperature control
Conventional biological treatment
processes
Downloaded from CivilDigital.com
 The ability of micro-organism to oxidize hydrogen
sulfide and other similar odorous compounds
dissolved in the liquid under aerobic conditions is the
basic concept
 In the activated sludge process, the odorous
compounds are introduced into the aeration basin
 But a major concern with this method is high rate of
corrosion in air piping and blowers that occurs due to
presence of moist air containing hydrogen sulfide
Downloaded from CivilDigital.com
Downloaded from CivilDigital.com
Thermal processing
 Three thermal processing techniques
are in use:
a) Thermal oxidation
b) Catalytic oxidation
c) Recuperative and Regenerative
thermal oxidation
Downloaded from CivilDigital.com
 If the gas to be combusted does not liberate enough
heat to sustain the combustion process, it is usually
necessary to use an external fuel source.
 As because most of the waste streams have low
concentration of odorous combustible gases hence
sustainable thermal oxidation is seldom possible
 To maintain the combustion temperatures needed to
eliminate odors, large amounts of fuel is required
Downloaded from CivilDigital.com
 Thermal oxidation involves preheating the odorous
gases before passing them into the combustion
chamber so that complete oxidation can be achieved
 Catalytic oxidation is a flameless oxidation process
that occurs in presence of catalyst (palladium,
platinum, rubidium etc.)
Decrease in temperature reduces the energy
requirements significantly.
As the catalyst can become fouled, the gases to be
oxidized must not contain particulate matter or
constituents that will result in residue
Downloaded from CivilDigital.com
 Recuperative and Regenerative thermal
oxidation processes are used to reduce fuel
consumption by preheating the incoming
air.
In recuperative oxidizers, thin wall tubes
are used to transfer heat recovered from
exhaust air to incoming air
In regenerative oxidizers, ceramic
packing material is used to capture the heat
from the hot exhaust gases and release it to
the incoming air.
Selection and design of odorcontrol facilities
Downloaded from CivilDigital.com
 Determine the characteristic and volumes of the gas to




be treated
Define the exhaust requirements for the treated gas
Evaluate climatic and atmospheric conditions
Select one or more odor control and treatment
technology
Economic analysis
Downloaded from CivilDigital.com
References
 Metcalf and Eddy
 www.wikipedia.com
 www.wateronline.com
 www.omi-idustries.com
 www.thomasnet.com