Listed below is a typical process flow sheet for a wastewater treatment plant with a further description of the typical types of odors generated from this area of the process.
(click image to enlarge)
Collection Systems
Gravity Sewers
Reasons for Odors: pressurization of the sewer atmosphere force odorous air from the various structures along the way (manholes, drop structures, reductions in pipe diameters, etc.).
Major odorant: H2S
Minor odorant: various odors derived from VOC and RSCs
Force Mains
Reason for Odors: sewer is under pressure and completely filled with wastewater, the result is a highly anaerobic conveyance system. Highly odorous air emerges where the force main wastewater is received.
Major Odorant: high concentration H2S
Minor Odorant: various odors derived from VOC and RSCs
Pump Stations
Reason for Odors: receiving various qualities of wastewater and is a source of potential release to ambient atmosphere
Major Odorant: low concentration H2S
Minor Odorant: various odorous compounds and low level VOCs
Commercial or Industrial Discharges
Reason for Odors: high temperature and high BOD wastewater that causes the depletion of dissolved oxygen and sulfide generation.
Major Odorant: various odors derived from VOC and RSCs
Minor Odorant: H2S
Odor Emissions from Liquid Stream Wastewater
Preliminary Treatment
Processing Equipment: Odorous emissions are highly dependant on the characteristics of the influent wastewater: source of wastewater, detention time, turbulence, characteristics and volume of wastewater return from down stream processes.
Influent Pump Stations
Grit Chambers
Pre-aeration basins
Influent Channels and Distribution Boxes
Flow Equalization Basins
Major Odorant: H2S
Minor Odorant: various odors derived from VOC and RSCs
Primary Treatment
Processing Equipment: A major source of odor emissions, but due to the large odor-emitting surface area, the odors are not strong and persistent, rather objectionable. This is a major source of odors on a volume per volume basis.
Major Odorant: various low level odors
Minor Odorant: various low level odors
Biological Treatment
Processing Equipment: Activated-sludge process, fixed-film processes, final clarifiers, settling tanks. Low odor emission rates that are not well defined but described as musty odor or fresh character.
Major odorant: poorly defined, low level odors
Minor odorant: poorly defined, low level odors, H2S
Complex mixtures of RSC including H2S, VOCs, and ammonia.
Odor Emissions from Residual and Solids-Handling Processes
Complex mixtures of RSC including H2S, VOCs, and ammonia.
Thickening
Reasons for Odors: Odors emanating from settled solids and the grease and scum that accumulates on the surface. Gravity thickeners, DAF, gravity belt, and rotary drum thickeners.
Major odorant: non-H2S RSCs
Minor odorant:
Blending and Holding
Reasons for Odors: Excess holding times can increase the odors.
Major odorant: RSCs
Minor odorant:VOCs including VFAs and H2S
Stabilization
Reasons for Odors: Various processes: aerobic digestion, anaerobic digestion, thermophilic aerobic digestion, alkaline stabilization, wet-air oxidation.
Major odorant: Various mixed: RSC, H2S, ammonia, amines
Minor odorant: Various mixed: RSC, H2S, ammonia, amines
Dewatering
Reasons for Odors: Pending the characteristics of the feed sludge. Mechanical means of dewatering: belt filter presses (turbulent discharge of filtrate), centrifuges (cake discharge chute), plate-and-frame presses (low turbulence), and drying beds (large exposed area).
Major odorant: Odor, RSCs, H2S, ammonia
Minor odorant: H2S
Composting
Reasons for Odors: Aerated static pile, windrow composting, in-vessel composting
Major odorant: various odor
Minor odorant: H2S
Thermal drying
Reasons for Odors: Volatilization of odorous compounds due to the heat of drying.
Major odorant: various odor
Minor odorant: H2S
Incineration
Reasons for Odors: Various odors present and incomplete combustion can result in significant odor excursions.
Major odorant: various odor
Minor odorant: H2S
Cake Conveyance, Storage, and Transport
Reasons for Odors: Depends on the type of cake being handled. Hard to control as cake is handled with conveyors, front end loaders, etc.
Major odorant: various odor
Minor odorant: H2S
Land Application
Reasons for Odors: Is a function of the type of biosolids being land applied and the method of applying the biosolids.
Major odorant: various odor
Minor odorant: H2S
Grit, Screenings, and Scum
Reasons for Odors: Residuals from WWTP that typically are very odorous as a result of storage.
Major odorant: various odor likely due to organics
Minor odorant: various odor likely due to organics
