(EP528110-A1)      Biological treatment of O2-contg. waste gases contaminated with biodegradable cpds. is effected by contacting the gas with an aq. suspension of microorganisms.    The contact time between the gas and suspension is 0.5-10 secs. The suspension (circulated between the contact vessel and a dwell tank) is recontacted with the gas after a dwell time of 10-30 mins. A 5-50% portion of the total biosuspension hold-up is (continuously) replaced by a biosuspension contg. active mircrooganisms from the biological stage of a waste-water treatment plant.    The gas is pref. contacted with the suspension in one or more perforated-plate columns. The gas to liq. vol. ratio is 1:0.005-0.015. The gas contains less than 50 ppm contaminants. The biosuspension replacement rate is pref. less than 10.%.    USE -   Used for deodorising waste air contg. organic S cpds. or for removing methyl methacrylate and/or butyl acrylate from waste air    (DE4127267-C2)      Process for cleaning waste air contg. O2 and impurities comprises contacting the air with an aq. suspension of microorganisms. The contact time is 0.5-10 seconds; after 10-30 minutes the gas is contacted with the suspension again; and the suspension has an exchange rate of 5-50%, based on the hold-up of a biosuspension contg. active microorganisms from the biological step of a waste water purification plant, where the microorganisms degrade the same impurities as they remove them from the gas.    USE/ADVANTAGE -   The process is used to remove sulphur-contg. substances with a powerful smell, or methyl methacrylate and/or butyl acrylate. The process is suitable for low or relatively higher concns. of impurities. The appts. for the process is relatively simple and cheap. The process can be controlled to prevent damage to the microorganisms or excessive growth.    (JP95057302-B2)      Biological treatment of O2-contg. waste gases contaminated with biodegradable cpds. is effected by contacting the gas with an aq. suspension of microorganisms.    The contact time between the gas and suspension is 0.5-10 sec. The suspension (circulated between the contact vessel and a dwell tank) is re-contacted with the gas after a dwell time of 10-30 min. A 5-50% portion of the total bio-suspension hold-up is (continuously) replaced by a bio-suspension contg. active microorganisms from the biological stage of waste-water treatment plant.    The gas is pref. contacted with the suspension in one or more perforated-plate columns. The gas: liq. vol. ratio is 1:0.005-0.015. The gas contains less than 50 ppm contaminants. The bio-suspension replacement rate is pref. less than 10%.    USE -   For deodorising waste air contg. organic S cpds. or for removing methyl methacrylate and/or butyl acrylate from waste air    (EP528110-B1)      A process for treating waste gas in which the oxygen-containing waste gas contaminated with biodegradable compounds is contacted with an aqueous suspension of microorganisms a) for 0.5 to 10 seconds in one or more sieve-plate columns, b) the suspension is then delivered at least partly to a holding tank and, after a residence time of 10 to 30 minutes, is recontacted with the waste gas as in a), c) the biosuspension being exchanged for a biosuspension from the biological stage of a sewage treatment plant containing active microorganisms, in which inter alia the same pollutants to be removed from the waste gas are degraded, at an exchange rate of 5 to 50% h, based on the hold-up in the water system.