Evaluation of full-scale biofilter media performance

The objective of this study was to characterize the key physical, chemical and biological properties of compost media from a full-scale biofiltration system used to control VOC emissions. Results of media characterization were used to assess the need for operational changes and media replacement. Biofilter media properties evaluated included: moisture content, pH, total organic carbon (TOC) and nitrogen content in water extracts and solid matrix, oxygen uptake rates, and microbial plate counts including total heterotrophs, oligotrophs, actinomycetes and fungi. Samples were taken from various locations and depths in the biofilter after three and five years of system operation. Media moisture content was highly variable, with samples from deeper in the bed dryer than surface samples. Low moisture contents were associated with low pH values values and low oxygen uptake rates. Total organic carbon contents in water extracts were higher than typical biosolids compost in samples near the inlet to the biofilter, possibly due to extracellular polysaccharides. After five years of use, total nitrogen and organic carbon contents in the solid matrix did not significantly differ from initial levels or those in typical biosolids compost.