In the modern world of wastewater treatment, control of odors has moved from an afterthought to a primary design consideration for most collection and treatment facilities. As communities and other development increases in the areas surrounding these facilities, the need to address and control these nuisance odors becomes more important.

Most wastewater related odor control problems are generated via bacterial activity within the waste streams (typically referred to as liquid-phase odor). Inherently odor causing compounds are volatile and therefore are readily released to the air when given the opportunity, at which point they are referred to as vapor phase odor. Odor problems can therefore be effectively controlled in either phase, however, there are often practical or economic reasons to focus on a particular phase, or in an increasing number of cases, both.

There are many treatment technologies and options associated with odor control in the liquid phase.  However, once odors are released into the atmosphere and become vapor phase odors, other control strategies have to be considered. Vapor phase technologies ventilate/treat the point sources of odor such as wet wells, headworks, etc. Vapor phase treatment options are primarily focused on the removal of hydrogen sulfide (H2S). Methods for vapor phase odor control treatment typically include wet chemical scrubbers, biofilters/bioscrubbers, dry chemical scrubbers and activated carbon adsorbers.

Among these options, wet air scrubbing has proven to be one of the most flexible and reliable for vapor-phase wastewater odor control technology.  In addition to treating H2S and organic odors, wet scrubbing has also proven to be effective for ammonia removal. Wet scrubber design for these types or wastewater odors typically involve multi-stage, vertically orientated packed towers. The basic objective of the packed towers is to provide contact between the odorous air and scrubbing solution (water with pH-adjusting and/or oxidizing chemicals to dissolve and/or oxidize the odorous compounds. The commonly used chemicals are chlorine based (particularly sodium hypochlorite) and pH adjustment is typically accomplished via sodium hydroxide or sulfuric acid. Multi-stage, pre-engineered systems make for easy installation and reduce operation and maintenance costs.

Biofiltration is used within the wastewater industry to treat a variety of biodegradable, water-soluble contaminants. In a biofilter or bioscrubber, the odor contaminants are solubilized from the vapor-phase into an aqueous biofilm on the surface of an organic medium, such as compost, mulch or a longer-lasting, engineered, inorganic. Moisture content and temperature are important environmental conditions for proper microorganism growth within the biofilm. Bacteria then "consume" the odorous compounds via their natural metabolic processes.

Biofilters are effective at removing sulfur-based odor compounds, such as H2S, organic sulfides and mercaptans, when operated under proper moisture, temperature and loading conditions. They are generally not effective at removing nitrogen-based compounds such as ammonia and amines.

Dry scrubbers contain chemically treated media (most common designs utilize inert granular or extruded media containing potassium permanganate or iron oxide) to remove sulfur compounds from odorous air streams, reacting with them and converting them to stable compounds. Since the media is actually consumed, dry scrubbing or "scavenger-based" approaches to odor control are often limited to low levels of contaminants.

With carbon adsorption-based vapor-phase odor control methods, the odorous air stream is exposed to a bed of adsorbent material (carbon), which allows the odor-causing compounds to adhere to the porous surface of the activated carbon-based granules or pellets. Carbon adsorption systems are effective on H2S and related sulfur-based compounds, as well as other volatile organic compounds. Siemens' Midas Odor Control Media® has enabled significant loading increases in the practical application for H2S control. Carbon adsorber systems are available in a variety of sizes and support services including carbon delivery, installation and spent carbon reactivation are offered to help minimize direct labor resource requirements and maintenance.

Vapor Phase Odor Control Removal Technologies
Biofiltration
Carbon Adsorption
Wet Air Scrubbing