Source of Odors & Strategies for Odor Management
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.
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
Source of odor
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.
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
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.
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
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
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
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
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
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
- Installation of collection hoods and air handling equipment for directing the gases to treatment units
- Typical containment alternatives are reported in the table
Chemical additions to W.W. for Odor control
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
- 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.