Page 458 - Air Pollution Control Engineering

11_chap_wang.qxd 05/05/2004 5:19 pm Page 430
430 Gregory T. Kleinheinz and Phillip C Wright

Table 4
Summary of Important Properties of Common Biofilter Materials
Activated carbon,
perlite, and other Other inert
Property Compost Peat Soil inert materials materials
Natural micro- High Medium– High None None
organisms’ low
population density
Surface area Medium High Low– High High
medium
Air permeability Medium High Low Medium–high Very high
Assimilable nutrient High Medium– High None None
content high
b
Pollutant sorption Medium Medium Medium Low–high a None to high ,
capacity very high a
Lifetime 2–4 yr 2–4 yr >30 yr c >5 yr >15 yr
Removal efficiency Low Low Medium N.A. d N.A.
Maintenance High High Low N.A. N.A.
requirements
Space requirements Medium Medium High N.A. N.A.
Substance Low Low Medium N.A. N.A.
adaptability
Cost Low Low Very low Medium–high Very high
a Activated carbon;
b Synthetics coated with activated carbon;
c ref. 23;
d N.A. = not reported.
Source: Data from refs 23–25

some biofilter designs. Although these media may be appropriate, they are certainly not
appropriate for all applications. In fact, proprietary media are often very costly and do
not perform any better than other more readily available media. In one application, a
proprietary media costing several hundred dollars a cubic foot failed in 17 d, resulting
in significant downtime of the biofiltration system. The bottom line is to make sure you
are aware of the needs of your exact application and pick a medium that addresses your
application’s needs and special circumstances (if any). Further discussion and summary
of solid media choice is described in Table 4.

3.3. Microbiological Considerations
Although there are numerous engineering considerations to be aware of when
designing a biofiltration system, one should always remember that these considera-
tions would be meaningless without an active microbial population. The premise of
conventional biofiltration is that a chemical passes through the biofilter bed and is
transferred from the air phase to the liquid phase that surrounds the solid-support
materials. This liquid phase is a biofilm where the microorganismss degrade the
chemical of interest. Primarily, two forces affect the flux of chemicals from the air