Advances in next-generation odor control technology, such as biotrickling filters, often go unrecognized because they’re not well understood.
Next-generation odor control technology, such as biotrickling filters, takes the main principles of common biofilters and amplifies their effect.
But these advances —and the advantages they present over more rudimentary biofiltration processes— often go unrecognized because they’re not well understood.
A greater understanding of the biology in the biofiltration process will allow facility owners and plant managers to better judge which of the available industrial odor control solutions is best for their site.
Principles of biofiltration
Biofiltration differs from other industrial odor control methods in that microorganisms feed on odorous compounds in the air rather than eliminating the compounds using harmful chemicals or adsorption by carbon filters.
These microorganisms include many different bacteria and fungi that break down offending compounds to get their energy. Clean air ready to safely discharge is released from the vessel and water run through the system drains off the byproducts.
Biofiltration, and especially the use of biotrickling filters, has repeatedly proved to be a more viable —and potentially better and cheaper— odor control solution compared to more common methods such as biofilters, chemical scrubbers or carbon systems.
Biodiversity in the biofiltration process
The workhorses of the biofiltration process are aerobic bacteria that derive their energy by consuming odorous compounds in the air. These bacteria are made up of acidophiles and neutrophiles. The former thrive in acidic environments (with a pH of around 2.0 or lower) while the latter prefer neutral environments. These bacteria can also be either autotrophic or heterotrophic. Both autotrophs and heterotrophs are used in biotrickling filters because it allows these systems to remove a wider variety of odors.
- Autotrophic bacteria do not require organic carbon-based material for cell growth. Instead, they use the gaseous CO2 in the air as their carbon source for cell growth. Examples of odors eliminated in this way are ammonia (NH3) and hydrogen sulfide (H2S). These bacteria are either acidophilic or neutrophilic.
- Heterotrophic bacteria usually rely on organic compounds as their carbon source for cell synthesis. These organisms are the type most responsible for decomposition in natural environments. Heterotrophs consume organic odor compounds such as methyl mercaptan (CH3SH), dimethyl sulfide ((CH3)2S) and dimethyl disulfide ((CH3)2S2). They also consume volatile organic compounds (VOCs). These bacteria are mostly neutrophilic.
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System design in the biofiltration process
The design of a biotrickling filter lends itself well to biodiversity within it. That’s because the environment within the vessel can be controlled to support the growth of a particular bacteria required for the removal of a certain foul air compound, or a variety of bacteria to remove multiple compounds.
For example, H2S oxidation is carried out by acidophilic bacteria that produce acidic by-products, whereas VOC removal is done primarily by neutrophilic bacteria. Biotrickling filter systems can be designed to support the growth of differing bacteria based on a site’s unique needs, whether it’s the elimination of a single odorous compound or the elimination of many.
The complementary relationship between acidophilic and neutrophilic bacteria within the reactor eliminates a wide variety of organic and inorganic odorous compounds. But the biology within the biofiltration process cannot work as intended without several important ingredients: water, nutrients and the media through which the water and air flow.
Biotrickling filters contain synthetic media featuring much greater surface area than that of organic media materials like peat moss or wood chips used in common biofilters. That high surface area allows more bacteria to thrive per cubic inch and treat more odorous air within the volume of the vessel, effectively making the odor control vessels very compact.
The water that trickles downward through the vessel serves two important functions. First, it creates a wet environment that the bacteria need to consume the compounds. Second, it collects the byproducts of that consumption on its way down and out of the vessel.
The microbial growth within biotrickling filters depends on nutrients that are either added externally in small doses along with irrigation water or inherent in the media. The types of nutrients used and the way they’re incorporated into a system depend on the system’s design and operating parameters.
The ability to control process parameters and customize the biological environment within the system makes biotrickling filters able to handle much higher odor loads within more confined spaces and footprints. That’s coupled with minimal maintenance, the absence of any dangerous chemicals and the potential for substantial capital and operating cost savings.