Microbial Populations of Biofilters

Microbial population distribution along biofilters has recently been reviewed by Benedusi et al. (33). The purifi cation of waste air containing a limited number of pollutants is effectively achieved by a population restricted to a few microbial species and generally requires, to shorten the start-up operation time, inoculation of the biofilter with pure cultures or activated sludges previously adapted to each pollutant. This practice is particularly suited to the degradation of very recalcitrant or complex organic pollutants, such as halogenated and aromatic hydrocarbons, which often require cometabolism with more easily de-gradable substances to accelerate the process (34,35). On the other hand, gaseous emissions simultaneously polluted by several compounds, such as those coming from water works, compost plants, and so on, require as inoculum a more heterogeneous population possessing a wider variety of metabolic pathways, which is available in the microorganisms naturally present in activated sludges and compost. Microbial loads of about 105, 104, and 103 colony-forming units per gram of support (CFU/g) have been reported for oligoheterotrophic, copioheterotrophic, and autotrophic metabolic types, respectively in heather-peat biofilters treating septic-tank emissions (33). Although Bohn (3) demonstrated that enriching compost-based biofilters with microorganisms is not advantageous in terms of removal yields, probably because of the unfavorable competition with the indigenous population, the addition of activated sludges to medium devoid of microorganisms

Table 2. Typical Pollutants Removed by Biofiltration, in Addition to Odor Control, in Different Industrial Applications

Organics

Type of Industry

Inorganics

Aliphatic Aromatic compounds compounds compounds compounds H2S NH3

Oxygenated S-containing N-containing Halogenated

Food and Agriculture Industry

Aroma extraction Yeast drying

Blood and fish-meal production Bristle and feather drying Fish roasting Fat processing Gelatin production Coffee and cacao roasting Bone processing Meat and fish curing Animal feed production Slaughterhouses Tobacco processing Livestock farming

Foundries

Plastics processing

Lacquer production and processing

Adhesive production

Oil and fat production

Polyester manufacture

Friction-linings production

Rendering plants

Glue production

Used oil processing Dump gas removal Sewage treatment and sludge drying Composting and waste processing Manure drying

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