Characterization of compost biofilter media
The goal of this study was to determine the physical, chemical and biological properties that can be used to determine the performance of compost as biofilter media. Four types of compost were characterized with regard to pH, total organic carbon and nitrogen content in solid matrix and water extracts, moisture content, oxygen uptake rates, and microbial population densities. Compost were blended with ceramic pellets and oyster shell into three media mixtures: biosolids (BS), yard waste (YW) and a biosolids/horse manure mixture (BSHM). Performance was determined in laboratory scale systems treating a mixture of VOCs under different operational conditions. Media from a full-scale biofilter was also characterized and its properties related to system performance.
Performance was closely related to compost quality characteristics. Initial high oxygen uptake rate and soluble total carbon of BSHM shortened the acclimation period. After severe drying, however, rewetting of BSHM could not be achieved. High water holding capacity, good rewettability and low compaction of YW resulted in sustained high removal efficiencies over the operation period. Rewetting after drying was achieved for BS and YW media.
Among the four compounds present in the VOC mixture, ethanol was degraded sooner followed by butyraldehyde, ethyl acetate and 1,1-diethoxy butane(DEB). Media drying resulted in ethyl acetate and DEB removal efficiencies decreases due to reduction of active biofilter. The highest total VOC elimination capacities reached by the media were 197, 210 and 241 g/$\rm m\sp3$-hr on a total VOC basis for BSHM, YW and BS respectively.
After 300 days of operation, biofilter media was re-characterized. Profiles with depth were observed for moisture content, volatile solids, water extracted total organic carbon, solid matrix total nitrogen, pH and oxygen uptake rate. Oxygen uptake rates increased in BS and YW, indicating higher microbial activity of VOC degrading organisms. Insignificant changes in total nitrogen, volatile solids, and pH were observed. Water extract total organic carbon and fungi density increased in all media.
In the full-scale system, low oxygen uptake rates were related to dry areas. High compaction, hydrophobicity and fine particle sizes indicated media deterioration. Moisture content heterogeneity indicated a need for moisture addition system improvements.
0542: Chemical engineering