NOVELTY - A bio-filter media comprising several grains (42) having a porous hydrophilic nucleus (44); and a hydrophobic coating (46) on the hydrophilic nucleus, is new. The hydrophobic coating comprises a metallic agent; microorganisms; nutrients; organic carbon; an alkaline buffer; a bonding agent; an adsorptive agent and a hydrophobic agent. The metallic agent is in powdered form prior to formation of the hydrophobic coating.    USE - To remove hydrogen sulfide (claimed); for cleaning contaminated air or waste gas e.g. organic sulfides and volatile organic compounds (VOC) such as chlorinated organics from air streams.    ADVANTAGE - The presence of metallic agent preferably iron in the hydrophobic coating allows the removal of sulfur by formation of iron sulfide and serves to enhance the conversion and biological processing of sulfur compounds in the contaminated air. Further, without the presence of iron or metallic components, biological oxidation of sulfur compounds may lead to elemental sulfur deposits on the bio-filter media. With the bio-filter media there is not a lengthy adaptation period or a need to add inocula. The bio-filter media start-up is almost immediate and usually in less than a day. This is unlike conventional bio-filter systems that may take a few days to become efficient. The presence of iron also helps the bio-filter media to handle periods of higher load (shock-loading) by reacting with excess contaminants. The catalytic properties of both the metallic agent and the hydrophobic coating reduce the adaptation period of the bio-filter media as well as the volume of bio-filter media required to treat a fixed volume of air contaminant. Lower bio-filter media volume in turn permits the installation of much smaller and much less expensive bio-filter systems. The grains includes a reservoir of water in the hydrophilic nucleus, which sustains transport of the contaminants from gas to liquid phase and supports biological activity throughout the surface area of the bio-filter media and aids in keeping the bio-filter media from drying out. The hydrophobic coating acts as protection to the hydrophilic nucleus by preventing excess water retention on the surface of the grains, which might otherwise cause excess formation of bio-mass and subsequent resistance to gas flow and, thus, a decrease in the efficiency of the bio-filter media. The bio-filter media is able to remove hydrogen sulfide at low (down to approximately 2.0) and neutral pH ranges. The bio-filter media has a lower empty bed residence time (EBRT) than the known bio-filter media, which facilitates the removal of higher concentrations of sulfides at lower EBRT's. Approximate neutral pH can be maintained by simple irrigation of the bio-filter media without the need of chemical additives. The bio-filter media provides uniform performance under cyclic shock loading under negative pressure. The bio-filter media can be washed easily to remove by-products of hydrogen sulfide oxidation. The inclusion of metallic agent and more particularly iron, improves the removal efficiency of air contaminants and nuisance odors, particularly hydrogen sulfide, reduced sulfur compounds and inorganic sulfur along with volatile organic compounds such as those found in industrial facilities, municipal plant facilities and exhaust air streams by increasing the reaction rate of chemical conversion followed by biological oxidation. Intermediate by-products resulting from chemical reactions such as conversion by the metallic agent are easily biodegradable and do not deposit in the bio-filter media causing a reduction in the life cycle. The ability to add water to the bio-filter media not only provides a wetting property for the continuation of biological oxidation, but also serves to maintain the proper air and bio-filter media temperature for supporting a high rate of metabolism in the bacteria. The bio-filter media that can be used to remove sulfur based compounds and VOC's at a high concentration, high flow rate and variable pH while extending the life span of the bio-filter media and decreasing the adaptation period. The bio-filter media is also more uniform in composition than conventional bio-filter media. In addition, due to its composition, the bio-filter media does not easily compact. Thus, the bio-filter media provides less gas flow resistance (low pressure drop) so that energy consumption required for gas flow through the media is lower. These features increase the long-term efficiency and the serviceable life of the bio-filter media and therefore, the life span of the bio-filter system.    DETAILED DESCRIPTION - An INDEPENDENT CLAIM is included for a method of operating the bio-filter system.    DESCRIPTION OF DRAWING(S) - The drawing shows a conceptual illustration of the grain of the bio-filter media.    Grains (42)    Porous hydrophilic nucleus (44)    Hydrophobic coating. (46)