In conventional biofilter operation, contaminated air is passed continuously through packed beds containing microbial consortia capable of contaminant biotransformation. This paper describes how biofilters can be designed and operated as controlled unsteady-state, periodic processes for the destruction of gas-phase contaminants. Such operation, previously limited to applications in wastewater treatment and soil remediation, increases an operator's ability to control the physiological state, “robustness,” and spatial distribution of the microbial communities established within the biofilter and, thus, minimizes uncertainties that often accompany design and operation of biological systems. Results are presented from toluene degrading biofilters that used polyurethane foam packing medium. These studies demonstrate how controlled periodic operations can enhance contaminant removal during transient periods of elevated contaminant load.

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