Page 471 - Air Pollution Control Engineering

11_chap_wang.qxd 05/05/2004 5:19 pm Page 443
Gas-Phase Biofiltration 443

Pressure drop across 2 1 One of the most critical factors to monitor
biofilter bed and very inexpensive. Increases in press-
ure drop across a biofilter bed can indicate
microbial overgrowth on the solid support.
This overgrowth can lead to log-order
inc-reases in microbial growth and
increasing pressure drops. These large pre-
ssure drops can lead to large increases in
electrical costs due to increased work by
the motors to move air through the sys-
tem. Since these electrical costs are often
one of the largest operating expenses, large
pressure drops can drastically increase
operational costs. Large pressure drops can
be a prelude to complete system failure.
Relative humidity (RH) of 2 1 This is an inexpensive parameter to monitor.
the influent air Since the influent portion of many large-
scale systems is difficult to access, this
assures the operator the influent zone poss-
esses adequate moisture. Influent air
should be 99.9% RH for best operation.
Temperature 1 1 Easy and inexpensive parameter to monitor.
Used to help assess if temperature changes
can be a contributing factor to changes
in biofilter performance. Generally,
the closer to 70ºF the influentair is, the
better performance your system will have.
a Relative scale is 1–5 with 5 being the most important or costly and 1 being the least important or costly.
b This is very important (4) if the solid support is a natural material like wood chips or bark.
However, it is less important for materials that do not breakdown readily like many of the synthetic
solid supports.

NOMENCLATURE
2
2
A = Area (ft or m )
3
3
C = Influent concentration (g/m or lb/ft )
I
3
3
C = Effluent concentration (g/m or lb/ft )
0
3
3
V = Volume of biofilter bed (m or ft )
b
3
A = Airflow rate (m /minute or cfm)
r
EBRT = Empty-bed residence time (s or min)
TBRT = True bed residence time (s or min)
3
3
V = Volume of solid support (m or ft )
ss
M = Media porosity (%)
p
3
3
V = Volume of a given space (m or ft )
s
VL = Volumetric loading
RE = Removal efficiency
EC = Elimination capacity
∆p = Pressure drop across bed (kPa or psi)
bed