Removal of alpha-pinene from gases using biofilters containing fungi

Biofiltration is cost-effective for the treatment of gases containing low concentrations of volatile organic compounds $\text{(<3}\text{g}\text{m}{}^{\mathrm{-3}}\text{)}$. However, conventional biofilters, based on compost and bacterial activity, face problems with the elimination of hydrophobic compounds. Besides that, biofilter operational stability is often hampered by acidification and drying out of the filter bed. To overcome these problems, biofilters with fungi on inert packing material have been developed. Fungi are more resistant to acid and dry conditions than bacteria, and it is hypothesised that the aerial mycelia of fungi, which are in direct contact with the gas, can take up hydrophobic compounds faster than flat aqueous bacterial biofilm surfaces. Alpha-pinene was chosen as a model compound. It is an odorous compound emitted by the wood processing industry. In $\text{2}\text{l}$ biofilter columns four different packing materials were tested: perlite, expanded clay granules, polyurethane foam cubes and compost. The filters were inoculated with forest soil and ventilated with gas containing alpha-pinene. Start up took 1–2 months and removal efficiencies of more than 90% were observed, but mostly ranged from 50% to 90% due to overloading. In the filters containing perlite, clay, polyurethane and compost volumetric removal capacities of, respectively, 24, 33, 38 and $\text{24}\text{g}$ alpha-$\text{pinene}\text{m}{}^{\mathrm{-3}}$ filter $\text{bed}\text{h}{}^{\mathrm{-1}}$ were attained and the gas pressure drops in the $\text{60}\text{cm}$ high filter beds measured at a superficial gas velocity of $\text{35}\text{m}\text{h}{}^{\mathrm{-1}}$ were 70, 550, 180 and $\text{250}\text{Pa}$. The results indicate that it is possible to develop biofilters based on the action of fungi with higher elimination capacities for alpha-pinene as reported in literature for bacterial biofilters. The use of polyurethane foam cubes is preferred because of the low gas pressure drop in combination with a high volumetric elimination capacity.