Transient performance of biofilters treating mixtures of hydrophilic and hydrophobic volatile organic compounds

The biological degradation of hydrophilic and hydrophobic volatile organic compounds (VOCs), discharged in pulp and paper and wood products air emissions, was examined under transient operating conditions. Two identical bench-scale biofilters were operated in parallel in order to study the influence of step loads on the removal of alpha-pinene, a hydrophobic VOC, and methanol, a hydrophilic VOC. The biofilter media consisted of a mixture of wood chips and spent mushroom compost that was further mixed with either perlite or small-size wood chips. The biofilters provided complete methanol removals during the start-up period due to the absorption process followed by biodegradation. For alpha-pinene, however, there was an acclimation period of 1 week to 10 days before the biofilters achieved 100% alpha-pinene removal efficiency. Step changes in the methanol loading rate did not affect the performance of the biofilters with respect to methanol. However, these fluctuations significantly influenced alpha-pinene biodegradation provided enough time (i.e., several days) was allowed. The removal rate of alpha-pinene gradually decreased along the column after each step increase in methanol inlet concentration. It appears that the presence of high concentrations of methanol, a hydrophilic and easily biodegradable compound, adversely impacted the growth of the alpha-pinene degrading microbial community, thereby decreasing alpha-pinene removal capacity of the biofilters over time. Unlike alpha-pinene, the methanol biodegradation rate was not affected by the presence or absence of alpha-pinene and with alpha-pinene fluctuations in the inlet airstream.