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428 Gregory T. Kleinheinz and Phillip C Wright

Table 3
Elimination Capacity Values for Several Biofilter Applications
−3 −1
Chemical Maximum elimination capacity (g h ) Ref.
Acetone 280 12
BTEX 30 15
Hydrogen sulfide 130 16
JP-4, jet fuel 65 17
Methanol 300 18
MEK 120 19
α-Pinene 35 20
Styrene 100 21
Toluene 100 22

and so on, the term “removal efficiency” (RE) is used to express the percentage of the
influent chemicals removed by the system. RE is defined as
 C × C 
RE =  I 0  × 100 (5)
 V f 

3
where C is the concentration of the effluent (g/m ). The term “elimination capacity” is
0
utilized to express the overall effectiveness of the biofiltration unit and is generally
expressed as
(C × ) ×C A
EC = I 0 f (6)
V
f
or simply as
EC = ( RE) × ( VL) (7)

Elimination capacity is the best measure of overall biofilter performance, although,
in some instances, effluent concentrations only are used for regulatory compliance.
These are used for compliance purposes because many permits are based on the total
mass that may be released regardless of effectiveness of the treatment system being
used. A usual necessary (legislation dictated) RE will be in the range of > 95–99%, but
at low influent loads, the REs will be approx 100%. However, as the loading increases,
the RE will drop below 100%. This is called the “critical load” and is used in pilot sys-
tems to help size full-size units for optimal performance. Table 3 lists some ECs for a
variety of chemicals being treated via different biofiltration systems.
Generally, commercial biofilters will remove anywhere from 10 to 280 g h . The
−3 −1
higher removal is typical observed in highly water-soluble and easily degraded com-
pounds such as acetone and methanol, whereas lower rates are observed with more
complex and less water-soluble compounds such as α-pinene.
3.2. Biofilter Media

The choice of a solid-support medium for a biofiltration system could be the most
critical decision in the design of these treatment systems. Solid-support media may be