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BY:- dinesh Downloaded from Contents: Why do we need this Types of odors Source of odors Movement of odorous gases Strategies for odor.

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Presentation on theme: "BY:- dinesh Downloaded from Contents: Why do we need this Types of odors Source of odors Movement of odorous gases Strategies for odor."— Presentation transcript:

1 BY:- dinesh Downloaded from

2 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 Downloaded from

3 Why do we need odor management?? 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. Downloaded from

4 Types of odors Most of odorous compound typically contain either sulfur or nitrogen Rotten egg smell of hydrogen sulfide is the odor encountered most commonly ODOROUS COMPOUNDODOR THRESHOLD ppm CHARACTERISTIC ODOR Ammonia46.8Pungent, irritating Methyl Amine21.0Putrid, fishy Chlorine0.314Pungent, suffocating Hydrogen sulfide0.00047Rotten egg Downloaded from

5 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

6 LocationSource/ causeOdor potential Air release valvesAccumulation of odorous gases released from waste water High CleanoutsAccumulation 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

7 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

8 LocationSources / causesOdor potential HeadworksRelease odorous gases generated in waste water collection system due to turbulence in hydraulic channel and transfer points High Screening facilities Putrescible matter removed by screeningHigh PreaerationRelease of odorous compounds generated in waste water High Grit removalOrganic matter removed with gritHigh Side stream returns Return flows from bio solids processing facilities High Primary clarifiersFloating sludge, scum, turbulence in effluent weir that release odor Moderate Aeration basinHigh organic loading, poor mixing, inadequate DO, solids deposit Low/moderate Secondry clarifierFloating solids, excessive solid retentionLow/ moderate Downloaded from

9 3 - sludge and Biosolids 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

10 LocationSource/ causeOdor potential ThickenersOdor release by turbulence, solids deposits, temperature increase High/moderate Aerobic digestion Incomplete mixing in reactorLow/ moderate Anaerobic digestion High sulfate contents in solids, leaking hydrogen sulfide gas Moderate/ high Sludge storage basin Lack of mixing, formation of scum layerModerate/ 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

11 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

12 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

13 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


15 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

16 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

17 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 Downloaded from

18 Odor containment & treatment measures 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 sewersSeal existing access ports. Eliminate the use of structure that create turbulence Bar racksCover existing units Grit chamberCover the aerated grit chamber and in conventional type reduce turbulance Primary and secondary sedimentation tanksCover existing units, replace overflow weirs with submerged weirs Sludge thickenerCover existing units Transfer channelsUse enclosed transfer channels Downloaded from

19 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 (-). Chemical additions to W.W. for Odor control Downloaded from

20 Use of odor Masking and Neutralization 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. Downloaded from

21 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.

22 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

23 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. Downloaded from

24 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 + 2H2OpH<8.5

25 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. Downloaded from

26 Effectiveness of hypochlorite wet scrubbers for removal of several odorous gases Gas Expected removal efficiency, % Hydrogen sulfide98 Ammonia98 Sulfur dioxide95 Mercaptans90 Other oxidizable compounds70-90 Downloaded from

27 Design consideration for chemical scrubbers ItemUnitsValue Packing depthm1.8-3 Gas residence time in Packing s1.3-2 Scrubbing liquid flow rate Kg H2O/kg airflow1.5-2.5 pHUnit less11-12.5 TemperatureDegree centigrade15-40` Caustic usageKg NaOH/kg sulfide2-3 Downloaded from


29 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


31 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

32 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

33 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 Downloaded from

34 Design considerations for odor- control Bio-filters 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 Downloaded from

35 Conventional biological treatment processes 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


37 Thermal processing Three thermal processing techniques are in use: a) Thermal oxidation b) Catalytic oxidation c) Recuperative and Regenerative thermal oxidation Downloaded from

38 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

39 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

40 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. Downloaded from

41 Selection and design of odor- control facilities 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

42 References Metcalf and Eddy Downloaded from

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