Biofiltration of n-butyl acetate with three packing material mixtures, with and without biochar

Two cost-effective packing materials were used for n-butyl acetate removal in lab-scale biofilters, namely waste spruce root wood chips and biochar obtained as a byproduct from a wood gasifier. Three biofilters packed with spruce root wood chips: without biochar (SRWC), a similar one with 10% of biochar (SRWC-B) and that with 10% of biochar impregnated with a nitrogen fertilizer (SRWC-IB) showed similar yet differing maximum elimination capacities of 206 ± 27, 275 ± 21 and 294 ± 20 g m^-3 h^-1, respectively, enabling high pollutant removal efficiency (>95% at moderate loads) and stable performance. The original biochar adsorption capacity was high (208 ± 6 mg_toluene g^-1), but near 70% of it was lost after a 300-day biofilter operation. By contrast, the exposed impregnated biochar drastically increased its adsorption capacity in 300 days (149 ± 7 vs. 17 ± 5 mg_toluene g^-1). Colony forming unit (CFU) and microscopic analyses revealed significant packing material colonization by microorganisms and grazing fauna in all three biofilters with an acceptable pressure drop, up to 1020 Pa m^-1, at the end of biofilter operation. Despite a higher price (14 vs. 123 €m^-3), the application of the best performing SRWC-IB packing can reduce the total investment costs by 9% due to biofilter volume reduction.