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Soil biofilters and related systems based on the use of natural filter beds have been used for several years for solving specific air pollution problems. Over the past decade, significant improvements have been brought to these original bioprocesses, among which the development and use of new inert packing materials. The present paper overviews the most common inert packings used in biofiltration of waste gases and their major characteristics. A potential problem recently encountered when using inert filter beds is the heterogenous distribution of biomass on the packing material, and the excessive growth and accumulation of biomass when treating high organic loads, eventually leading to clogging of the biofilter and reduced efficiency. Several strategies that have been proposed for solving such problems are described in this paper. Technologies for controlling excess biomass accumulation can be grouped into four categories based on the use of mechanical forces, the use of specific chemicals, the reduction of microbial growth, and predation.