The objectiw ofthis stud was to characterize the key chemical and biologica t " properties of compost f B me ia properties eva f uated included. moisture content, pH, fill-scale biofiltration system wed to control VOC emissions. Results of media characterization were wed to assess the need or o erational chan es and media replacement. Biofilter total organic carbon (TOC) and nitrogen content in water extracts and solid matrix, oxygen uptake rates, and microbial plate counts including total heterotrophr, oligotrophs, actinomycetes andfin . Sam les were takenjom various locations and depths in t e bioj ter afer three andfive years o system operation. Media moisture content was highly varia le, with samplesjom deeper in the bed dryer than su face samples. Low moisture contents were associated with low p H values and low oygm uptake ram. Total organic carbon contents in water extracts were higher than typical biosolidr compost in samples near the inlet to the biofllter, possibly due to extraclluhr polysacchads. Ajgfive years of we, total nitrogen and organic carbon conma in the solid matrix did not signiJcant-4 d z p j o m initial heh or those in typical biosolid compost. sf t P Environmental Progress (Val. 18, No.3) Fall 1999 205 Dryer exhaust I Cell # I Cell #2 Cell #3 coolinghumidification 'MC-Moisture content, VS-Volatile solids, OC-organic carbon. 'Determined in solid matrix. 30uR-Oxygen uptake rate in moisture nonadjusted respirometry. Numbers correspond to sample sites, letters correspond to different depths at the same sample site. Depths are indicated considering zero at the surface of the biofilter.