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Gas-Phase Biofiltration 425

Table 2
Disadvantages of Conventional Biological Odor Abatement Technologies
Conventional Conventional Conventional
biofilters tricklebed biofilters bioscrubbers
• Packing is usually non- • Biological overgrowth • More energy intensive
homogeneous, often leading to increased ∆p . than conventional
bed
preventing a uniform • Low specific area to packed-bed biofiltration.
gas distribution → reduce ∆p . • Because of the large
bed
shortcircuiting. • Drain water has to be amount of liquid, there
• Low specific gas flow continuously separated is a danger of active
(average for compost from excess biomass microorganisms being
3
beds 150 m gas/h/m 2 before being recycled. carried away.
bed, max. up to 500 m 3 • Fresh water must be • More sensitive than
2
gas/h/m bed). constantly fed to the packed-bed biofilters to
• Aging phenomenon, system because of losses. feed fluctuations.
resulting in: • Nonhomogeneous • Operation takes place in
• Lumping. temperature and more than one unit. The
• Drying out concentration profiles. sludge tank often
• Developing of requires extra stirring
anaerobic zones and oxygenation.
because of moisture • Periodic removal of
accumulation. sludge.
• Development of
shrink cracks
• Bed compaction
• Difficulty in
maintaining an
even bed pH

address these limitations, so that biofilters may be used in a wider range of applications.
If gas-phase biofiltration is going to receive increased takeup industrially, it is vital that
the stability, efficiency, and range of operating conditions are improved. This section
briefly addresses a number of the potential emerging technologies.
2.2.1. Pollutant Solubility in the Aqueous Phase
As described earlier, pollutant solubility may be an issue dictating method choice.
Some researchers have attempted to address the limitations of water solubility by using
surfactants in the biofiltration beds (7,8). The theory is that the increased solubility of
the chemicals in the bed will increase partitioning into the liquid phase and thus make the
chemicals more bioavailable. Lab studies have met with some success in applications
dealing with chemicals produced by the forest products industry. In addition to attempts
to increase solubility, changing the airflow rate has also been attempted. Because the
process generally sets the airflow rates, the changes have to be made prior to the biofil-
tration system. These changes in flow rate are accomplished via adsorption/desorption
systems; that is, high-flow, low concentrations are adsorbed on to a suitable substrate
(i.e., activated carbon) and are then desorbed at a lower flow rate and possibly higher