Pilot Scale and Real Scale Applications

Biofilters of different sizes (areas ranging from 10 to 2,000 m2) are currently used in many industrial sectors, mainly in Europe, to remove a variety of mixtures of volatile organic and inorganic compounds from off-gases characterized by variable flow rates (1,000-150,000 m3 h— 1) and low pollutant concentrations (usually less than 1,000 ppm). As one can see from Table 1, where the main pollutants removable by biofiltration are listed (3,13,16,26,27), a relatively variable degradability characterizes not only the different classes of pollutants, but also the various pollutants within the same class. While for easily biodegradable substances the microorganisms suited for their degradation are usually present in the natural packing materials, in-

Table 1. Classification of the Main Pollutants that can be Removed by Biofiltration, according to their Biodegradability

Excellent

Good

Minimum

Uncertain

Butadiene

Aliphatics

Aromatics

Aliphatics Hexane

Ethyl benzene, xylene Cresols

Nitrogenous

Trimethylamine

Oxygenated

Alcohols: butanol, ethanol, methanol

Aldehydes: acetaldehyde, formaldehyde

Esters: Ethyl acetate

Ethers: Tetrahydrofurane

Ketones: Acetone

Organic acids: Butyric acid

Sulfuric

Methyl mercaptan

Inorganics

Benzene, toluene Phenols

Aromatics styrene,

Halogenated Chlorophenols

Nitrogenous

Amides Heterocycles:

Pyridine Isonitriles

Nitriles: Acetonitrile

Oxygenated Methylisobutylketone

Sulfuric

Heterocycles: Thiophene Thiocyanates Thioethers:

Dimethylsulphide

Alicyclics Cyclohexane

Aliphatics Methane, pentane

Aromatics PAH

Halogenated

Carbon tetrachloride Dicloroethane Dichloromethane Pentachlorophenol Perchloroethylene Trichloroethane Trichloroethylene

Nitrogenous Nitrocompounds

Oxygenated Dioxane

Sulfuric Carbon disulfide

Halogenated 1,1,1-Trichloroethane

Aliphatics Acetylene

Nitrogenous Isocyanates

Oxygenated

Methyl methacrylate

Sulfuric Isothiocyanates

oculation and enrichment with cultivated organisms is often necessary for the slowly biodegradable ones.

On the other hand, Table 2 provides a picture of the most significant industrial sectors where biofiltration is applied with success, with indication of the related pollutants (26).

Finally, from Table 3, where the results of the principal pilot and full-scale applications of biofilters are summarized, it is evident that conversion yields often higher than 90% are not uncommon in industrial practice (16,17,20,2732).

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