Biological Treatment of Air Pollutants
Using MultiPhase™ Technology

The biological treatment of air
pollutants has been practiced
extensively for 15 years. In most
cases, the emphasis has been on
odor treatment rather than treatment
of volatile organics (VOCs).

Commercial-scale Biofilters can be categorized
into two main types: (1) Natural Media Biofilters,
which use compost, wood chips, soil, pine needles, etc. to biodegrade the contaminants; and (2)
Synthetic Media Biofilters that use biomedia
made from plastic, inorganic materials, etc.
Detailed analysis of the various biomedia
used in Biofilters has been recently presented
(Govind and Narayan, 2007).

Natural medias suffer from several disadvantages including clogging due to biomass growth,
and large footprint  - a challenge resulting in systems that are designed in-ground. Other
disadvantages include significant gas-phase pressure drop, the inability to handle solid
particulates in the gas phase and eventual consumption of the media, requiring replacement.

Over the last decade, Biofilters with engineered synthetic media emerged with a smaller footprint,
higher biodegradation rates, lower gas-phase pressure drop and the ability to wash-off the
excessive biomass growth (Govind, 2004). The synthetic biomedia had significantly higher
surface areas, did not require eventual media replacement, and were used in treatment
systems designed like chemical scrubbers.

In the literature, different terms are used to denote the method of contacting the contaminated
gas stream with water to maintain bioactivity. In a common Biofilter,  incoming contaminated
gas is pre-humidified, and the organisms reside on a solid surface of biomedia, where
degradation of the compounds occurs.

In a Biotrickling Filter, water is recirculated through the biomedia bed, thereby humidifying the
gas stream and providing water to the organisms attached to the biomedia surface. In a third
approach, the term “Bioscrubber” has been applied when water containing organisms, (from
an activated sludge water treatment system, for example) is recirculated through the biomedia,
thereby providing active organisms for degradation of the contaminants in the gas phase.

Biological Treatment of Air Pollutants
Using the MultiPhase BioSystem

The MultiPhase™  BioSystem overcomes all the disadvantages of conventional bioscrubbers
designed for the biological treatment of air pollutants by treating incoming contaminants in the phase
(liquid or gas) in which the contaminant would normally reside, depending on its inherent properties.

For example, a highly volatile compound with low water solubility will concentrate in the gas phase,
and will be treated mainly in the gas phase.  Highly water-soluble compounds with low volatility
will concentrate in the water phase and will be treated in the water phase. Most compounds with
intermediate volatility and water solubility will be treated in both the gas and water phases,
depending on their natural partitioning.

Biofilters and Biotrickling Filters attempt to treat all the contaminants in the gas phase, whereas
conventional Bioscrubbers delegate the treatment of the water-soluble fractions of the contaminants
to an external treatment system, often with design flaws that can either partially re-entrain the
contaminants into the ambient environment (due to air-sparging) or allow the contaminants to
accumulate and escape through the water.

Further, none of these systems – biofilter, biotrickler, or bioscrubber -- are designed to:

• handle particulate in the gas phase
• treat condensable with high molecular weight
• handle the dissipation of heat if the incoming gas stream is above
  the normal operating temperature of aerobic organisms (50°F to 105°F.)

The Tri-Mer MultiPhase can handle much higher inlet temperatures,
from dryers for example. Often, exhausts from press vents and dryers are
treated together, producing significant cost advantages.

High natural gas costs have made RTO equipment undesirable for many companies. 
The low pressure drop MultiPhase BioSystem is a natural choice for the biological treatment of
air pollutants: operating costs are sustainably low – and there is no natural gas expense burden.