Page 450 - Air Pollution Control Engineering

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422 Gregory T. Kleinheinz and Phillip C Wright

Table 1
Industries That Have Used Biofiltration for Air Pollution Control
Animal facilities, large-scale Painting operations, large-scale
Automotive Petrochemical manufacturing
Chemical manufacturing Petroleum
Coatings Plastics manufacturing
Composting Printing
Ethanol production Pulp and paper
Food processing Rendering
Fragrance Semiconductor
Iron foundries Sewerage treatment
Landfill gas extraction Wood products

air emissions. Some of the impetus for this adoption was the Clean Air Act Amendments
(CAAA) that were put into place in 1990. This brought air emissions into the forefront
of legislative and regulatory agencies throughout the United States. In addition to for-
mal regulations, a lack of tolerance has been seen in recent years for unregulated odorous
emissions. These types of odorous emission are typical of wastewater-treatment facili-
ties and are largely unregulated. Prior to their adoption in the United States, biofilters
had enjoyed much success in Europe, particularly The Netherlands, as a viable treat-
ment alternative to a variety of air emission issues. In fact, the first biofilters are
rumored to date back several hundred years to the mitigation of odors from outdoor
privys; the first US patent was granted in 1957 to Pomeroy (1). However, early systems
often used porous soil materials as a solid support, and primitive piping systems are
used for airflow through the beds. These first attempts were moderately effective, but
they were prone to channeling and poor air distribution.
Biofiltration has come a long way since 1957 and the market is expected to increase
in the future. It has been estimated that the biofiltration industry would be over $100
million dollars in 2000 (2). To our knowledge, these numbers have not been verified,
although biofiltration companies in the United States have seen unprecedented growth
over the past 5 yr. Given the comparable capital costs of biofilters and low operating
costs relative to competing technologies, it is likely that the market will continue to
grow and evolve. For example, many wastewater-treatment facilities were constructed
in the 1970s and were placed at the outskirts of their respective communities. As a result
of urban growth and development, residential housing, offices, and businesses now sur-
round these once semirural locations. With increased exposure to populations of people,
wastewater-treatment facilities are under increasing pressure to mitigate odors on site.
Because it is usually not practical to move the facility, odor-control technologies must
be implemented on-site. It should also be noted that the wastewater industry is not the
only industry being impacted by decreased tolerance for odorous air emissions.

2. TYPES OF BIOLOGICAL AIR TREATMENT SYSTEM
2.1. General Descriptions
In conventional packed-bed biofilters (Fig. 1), the vessel contains a layer, often 1–1.5 m
thick, of some type of filter material such as compost or peat. The waste gas, which is