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parameters of the system to avoid such issues as drying out of the bed, compaction and
overgrowth of microorganisms, and pH decrease, to name just a few.
As more is being understood about microbial population dynamics in these systems,
the operational window for biofiltration systems is continually widening. It is imperative
that when biofiltration is being considered as a treatment technology, all factors be con-
sidered prior to design and start-up, so that some potential limitations can be overcome.
By using knowledgeable planning, the success stories of biofiltration will continue to
expand in both total number and diversity of applications.

8. CONCLUSIONS
Biofiltration technologies are gaining wider acceptance as a viable air treatment
technology. Biofilters are not applicable to all airstreams; however, recent development
of biofiltration technology has seen an ever-increasing range of applications. Recent
research and development of these systems has led to a better understanding of sizing,
operational, and microbiological aspects of the treatment process. Biofilters are no
longer the “black box” in which treatment takes place. We are now able to understand
the complex chemical and biological interaction that takes place in these systems to bet-
ter design them for a myriad of applications previously not considered appropriate
applications of biofiltration.
It is imperative that biofilters be sized and properly fitted to their intended applica-
tion. Too often, one biofilter design is adapted to many different applications with less
than satisfactory results. Although the same design may be applicable for several appli-
cations, it is important that each application be evaluated on its needs and specific
characteristics. These characteristics include airflow to be treated, concentration of
chemicals in the airstream, temperature of the airstream, biodegradability of the con-
taminants, and so forth. Once these considerations, and possibly others, are evaluated,
the choice to go with a biofilter can then be made. Once biofilters are decided upon as
the treatment method, the designers can work on sizing, geometry, solid-support mate-
rial, and so forth. depending on the characteristics of the airstream. It is imperative that
the unit be properly installed and “fit” to the specific application. A bench- or pilot-scale
trial is highly recommended in this context.
Once the biofilter is operational, a monitoring protocol must be implemented that
allows for the evaluation of performance and for the notification of the operator of any
upsets in the system. Because these are biological systems, it is imperative to find small
problems before they become large problems that require downtime of the system.
In principle, biofilters are very simple methods of air treatment. However, increased
understanding of the engineering and microbiology involved in the process has made
them one of the more difficult treatments systems to operate effectively; that is, it takes
a good understanding of engineering, the process stream being treated, and the microbi-
ology in the system to allow for the long-term operation of these systems. If properly
designed, operated, monitored, and maintained, a biofilter should allow for many years
of cost-effective air treatment. This cost-effective operation will likely save the operator
a significant amount (tens to hundreds of thousands of dollars, or more) in operational
costs over its lifetime when compared to alternative treatment technologies.