Gas-phase biofiltration is an effective technology for reduction of odors and trace-gas contaminants. Significant contributions to the technical literature regarding the characterization of biofilter media have been generated in the past two decades. Nevertheless, the information produced has not been systematically organized. The objective of this study is to demonstrate and document methods for physical characterization of gas-phase compost biofilters (GPCB). The inclusion of moisture content, compaction, and particle size effects in the determination of media bulk density and porosity, field capacity, drying rate analysis, water sorption isotherms, and resistance to airflow is demonstrated. Results indicated that: (1) higher moisture content led to about 2% reduction in porosity after compaction; (2) biofilter media sieved into three particle size ranges (12.5 mm \u3e PSR1 \u3e 8.0 mm \u3e PSR2 \u3e 4.75 mm \u3e PSR3 \u3e 1.35 mm) produced significantly different media field capacities, i.e., 52.8% (PSR1), 61.6% (PSR2), and 72.2% (PSR3) on a wet basis; (3) a drying rate analysis provides important information regarding media-water relations and can be potentially used for in situ indirect media moisture monitoring (as shown in previous work, changes in drying rate significantly affected ammonia removal and nitrous oxide generation); (4) the Henderson isotherm can be accurately used for dry organic media to determine the minimum moisture required for microbial activity; and finally (5) the combination of high airflow and high moisture content drastically increased pressure drop up to 65-fold (6350 Pa m-1) compared to the lowest pressure drop (98 Pa m-1). Further, the research community should integrate efforts to elaborate standard methods and protocols for physical characterization of gas-phase biofilter media before and during biofilter operation
