Performance, microbial ecology, and life cycle assessment of an activated carbon biofilter for methanol removal.

摘要

The forest products industry is responsible for producing valuable industrial chemicals, wood products, and consumer goods. However, processes involved in creating these materials at pulp, paper, and paperboard mills also generate hazardous air pollutants (HAPs), such as methanol, that are released during wood pulp production. With increasingly stringent regulations on methanol emissions, mills are continually seeking effective and cost efficient ways to control its release. Motivated by the need to study economical and environmentally friendly methanol control technologies, a bench-scale activated carbon biofiltration system was developed and evaluated for its ability to remove methanol from an artificially contaminated air stream. The biofilter contained a novel packing mixture of activated carbon, perlite, slow release nutrient pellets, and water retaining crystals, and showed excellent biofilm growth and close to 100% biological methanol removal, both with and without addition of an inoculum containing enriched methanol-degrading bacteria.; Design of the biofilter using an inoculum enriched for methanol-degrading bacteria also facilitated characterization of biofilm samples from a pulp and paper mill on the basis of selecting a biofilter inoculum and optimizing growth and activity in mixed culture. Studies of enriched cultures from the biofilm samples showed higher bacterial community diversity and methanol removal when using nitrate as the nitrogen source for enrichment, rather than ammonium.; Design and operation of this bench-scale system also enabled further investigation with microbial ecology and molecular techniques to characterize diversity of bacterial communities colonizing the biofilter over different points in time and under varied operational conditions. Amplification and separation of DNA from biofilter samples, using polymerase chain reaction (PCR) and denaturing gel gradient electrophoresis (DGGE), indicated that although bacterial diversity and abundance varied over the length of the biofilter, the populations rapidly formed a stable community that was maintained over the entire 138 days of operation and in variable operating conditions. Phylogenetic reconstruction of bands excised from DGGE gels indicated that the biofilter supported a diverse community of methanol-degrading bacteria.; Finally, the design and operation of the bench-scale biofilter provided parameters for use in a life cycle assessment (LCA) that compared raw materials and energy required and emissions and environmental impacts produced by construction and operation of a proposed photocatalytic oxidation (PCO)-biofilter system, to those associated with treatment using a more traditional regenerative thermal oxidizer (RTO). LCA results indicated that environmental impacts associated with construction of a RTO far outweighed infrastructure requirements of the PCO-biofilter system. However, the operating impacts to global warming and human toxicity for the PCO-biofilter system were higher than for the RTO, because of the replacement requirements of packing for the PCO reactor and biofilter, as well as the electricity requirement to operate the PCO reactor.