Pollution and Pollution Control - Environmental Biotechnology: Theory and Application - page 72

The available technologies fall naturally into three main types, namely, biofil-
ters, biotrickling filters and bioscrubbers. To understand these approaches, it is
probably most convenient to adopt a view of them as biological systems for
the purification of waste or exhaust gases. All three can treat a wide range of
flow rates, ranging from 1000 to 100 000m 3 /h, hence the selection of the most
appropriate technology for a given situation is based on other criteria. The con-
centration of the contaminant, its solubility, the ease of process control and
the land requirement are, then, principal factors and they interact as shown in
Table 4.4 to indicate the likely best approach.

Biofilters
As mentioned earlier, these were the first methods to be developed. The sys-
tem, shown schematically in Figure 4.2, consists of a relatively large vessel or
container, typically made of cast concrete, metal or durable plastic, which holds
a filter medium of organic material such as peat, heather, bark chips and the
like. The gas to be treated is forced, or drawn, through the filter, as shown in
the diagram. The medium offers good water holding capacity and soluble chem-
icals within the waste gas, or smell dissolve into the film of moisture around
the matrix. Bacteria, and other micro-organisms present, degrade components of

Table4.4 Odourcontroltechnologyselectiontable
Technology Compound Compound Process Land

concentration solubility control requirement

Biofilter Low Low Low High

Biotrickling filter Low-medium Low-high Medium-high Low

Bioscrubber Low-medium Medium-high High Low-medium

Figure4.2 Biofilter