The characteristics of peanut shells and palm shells used as packing media in biofilters treating air-contaminated with methanol, toluene or mixtures of methanol and toluene for over 200 days were investigated. Although the characteristics of the two packings were different, they both appeared suitable for use as media in biofilters treating air-contaminated with methanol or toluene, since their maximum Elimination Capacity (ECmax) values were comparable to those obtained using other media. The ECmax values for peanut shells were slightly higher than those for palm shells, and the peanut shells had a much lower bulk density, which would certainly have cost advantages. However, the results also showed that palm shells could retain their structural integrity better than peanut shells and so required replacing less frequently. This means that local availability and costs of the two materials are likely to determine which should be selected. Use of peanut shells or palm shells should be of considerable benefit to Thai industries considering installing biofilters to remove Volatile Organic Compounds (VOCs), as it makes the cost of bed packing materials much more affordable than if more conventional packing materials had to be used.

Volatile Organic Compounds (VOCs) are organic compounds that evaporate readily at room temperature. They are discharged with waste gas streams into the atmosphere by a wide range of industries, and many VOCs are not only significant air pollutants but also harmful to human health. Although the amounts of VOCs emitted in individual waste gas streams are often quite low, the cumulative impact of the emissions of VOC on the atmosphere is substantial. Hence many industrialized countries have introduced regulations requiring industries, even quite small ones, to remove most of the VOCs from their waste gases before these are discharged into the atmosphere.

In many developing countries, such as Thailand, industrial discharges of air pollutants, such as VOCs, are less strictly regulated. However, more stringent regulations, similar to those in developed countries, are expected and will be introduced in due course. In Thailand, this will have an impact on industries like the printing industry, where a majority of the printing inks are solvent-based and the solvents evaporate during the printing process. The rate of expansion of the Thai printing industry is rapid, as can be inferred from the fact that for label printing alone the number of items printed rose from 9.26 ´ 10⁸ pieces in 2000 to 15.9 ´ 10⁸ pieces in 2008 (The Office of Industrial Economics) hence substantial increases in VOC generation can be expected from this industry alone.

Many current technologies for controlling VOCs (e.g., thermal incineration, wet scrubbing, and adsorption onto activated carbon) are costly, especially in cases where pollutant concentrations in the waste gases are low (Mohseni and Allen, 2000). Since the VOCs are biodegradable, another possible alternative treatment is biofiltration. Biofiltration is inexpensive compared with the techniques mentioned above and very effective for treating large volumes (up to 10⁵ m³/h) of moist air streams with low concentrations (less than 5 g/m³) of biodegradable pollutants (Devinny et al., 1999). Furthermore, the technology is comparatively environment-friendly, as the process operates at ambient temperature; therefore, energy inputs to the process are small.

In a biofilter, the waste gas is passed through a shallow bed packed with some suitable inorganic or organic material. A microbial biofilm grows on the surface of the packings. As the gas passes through the bed, pollutants diffuse from the gas phase into the biofilm where they are converted by microorganisms into carbondioxide, water and new biomass (Deshusses, 1997).

Chemical Engineering Journal, Peanut Shells, Palm Shells, Bed Packing Media, Volatile Organic Compounds, Printing Industry, Cultured Microorganism Colonies, Scanning Electron Microscopy, Fungal Mycelia, Chemical Engineering, Microorganisms.