Application of biofiltration to the control of VOC emissions

Biofilters suffer from compacting problems that lead to increased pressure drops and very often the permanent blocking of the filter which must then be followed by material replacement. The two major process variables involved are the type and size of the support material. Two different kinds of VOCs (n-propanol and a mixture of methyl and ethyl alcohols named Alcohol 2A) were removed in a pilot scale aerated biofilter, packed with spherical balls of peat, specially produced for this purpose. These target compounds are present in the emissions from a Montreal print shop (flexographer). When waste gases were passed through the biofilter, the contaminants were absorbed by an immobilized bacteria culture, and were converted to carbon dioxide, water and biomass end products. The reactor was operated over a period of 11 months under various levels of input airstream pollutant concentrations and now tares of the contaminated airstream. The mechanical strength of the peat spheres, their excellent adsorption/absorption properties, their ability to retain moisture together with their pH buffering action provided an ideal biofiltration medium for a single stage, 2m high system. This paper presents the (macro)kinetics of the VOC elimination process, enabling the prediction of the filter bed elimination capacity with respect to operating conditions to be made. Also, qualitative observations of the elimination capacity and VOC concentration profiles have confirmed that the diffusion regime controls the process.