by:- dinesh downloaded from civildigital.com. contents: why do we need this types of odors source of...

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 Downloaded from CivilDigital.com

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 CivilDigital.com

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 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

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 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

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 CivilDigital.com

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 CivilDigital.com

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 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

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 Downloaded from CivilDigital.com

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

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 CivilDigital.com

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.

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. Downloaded from CivilDigital.com

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