Three identical glass biofilters with an overall height of 0.5 m, packing height of 0.4 m and internal diameter of 0.1 m equipped with standard construction and control elements (Figure 1) were used for testing of three packing materials: spruce root wood chips without any biochar (SRWC), spruce root wood chips with 10% (v/v) of biochar (SRWC-B) and spruce root wood chips with 10% (v/v) of impregnated biochar (SRWC-IB). The porosities of SRWC, SRWC-B and SRWC-IB packings were 0.564 ± 0.025, 0.553 ± 0.011 and 0.505 ± 0.008, respectively.
The experimental apparatus consisted of standard units providing the inlet air humidification, the liquid pollutant being dosed into air using a syringe pump, NE-500 (New Era Pump Systems Inc., USA) equipped with a 500 mL glass syringe (Setonic Inc., Germany). The system also contained an airborne ethyl acetate detector, VOC-TRAQ flow cell (AMETEK MOCON, USA) equipped with a Purple piD-TECH eVx photoionization sensor (AMETEK MOCON, USA), and a BSM medium dosage device with programmable peristaltic pumps, LC-Cube PPS-9K6 (Watrex Inc., Czech Republic). The biofilter bed pressure drop measured in Pa was determined using a U-shaped tube differential pressure manometer on 0 (dry packing), 1st (wet packing), 38th, 115th and 300th (last) days of the biofilter operation. n-Butyl acetate (PENTA Ltd., pure grade with minimum 99% content) was selected as a representative contaminant to simulate the real-world broad-range mixture of volatile odorous fatty acids and their esters emitted from a typical textile plant, Juta a.s. (https://www.juta.eu/, Czech Republic). The effect of loading types on the biofilter performance was tested for 300 days (Table 1). Two loading patterns were applied. One of them included the loading variation by air flow rate (V g , in a range of 8-24 L min -1 at C in of 500 and 100 mg m -3 ) to simulate waste air with a low pollutant concentration yet causing a pungent odor). The second loading pattern was based on the variation of inlet concentration (C in , in a range of 100-1500 mg m -3 at V g of 3, 6 and 12 L min -1 ) to simulate heavily polluted air with relatively low flow rates. The biofiltration performance was evaluated using standard biofiltration parameters, elimination capacity, organic load, removal efficiency and empty bed residence time defined as follows:
Elimination capacity (EC):
Organic load (OL):
Removal efficiency (RE): Empty bed retention time (EBRT):
where C in and C out are the inlet and outlet n-butyl acetate concentrations in air (g m -3 ), respectively; V b is the packed bed volume (m 3 ) and Q is the air flow rate (m 3 h -1 ).
A mixed enriched culture taken from a biofilter treating a mixture of acetone and styrene, which was defined and successfully used previously [12] (link) was applied as an inoculum. The inoculum contained culturable isolated and identified bacteria, Pseudomonas sp., Bacillus sp., Arthrobacter sp., yeasts, Rhodococcus sp., Komagataella pastoris and fungus Fusarium solani. The selected mineral medium composition (BSM) allowed one to control pH (as a phosphate buffer) and supply the biofilm with water and mineral nutrients. 30 mL of this medium were added twice a day to each biofilter. It had the following composition (concentration given in g � L -1 ): KH 2 PO 4 (2.3), K 2 HPO 4 (2.9), (
The experimental apparatus consisted of standard units providing the inlet air humidification, the liquid pollutant being dosed into air using a syringe pump, NE-500 (New Era Pump Systems Inc., USA) equipped with a 500 mL glass syringe (Setonic Inc., Germany). The system also contained an airborne ethyl acetate detector, VOC-TRAQ flow cell (AMETEK MOCON, USA) equipped with a Purple piD-TECH eVx photoionization sensor (AMETEK MOCON, USA), and a BSM medium dosage device with programmable peristaltic pumps, LC-Cube PPS-9K6 (Watrex Inc., Czech Republic). The biofilter bed pressure drop measured in Pa was determined using a U-shaped tube differential pressure manometer on 0 (dry packing), 1st (wet packing), 38th, 115th and 300th (last) days of the biofilter operation. n-Butyl acetate (PENTA Ltd., pure grade with minimum 99% content) was selected as a representative contaminant to simulate the real-world broad-range mixture of volatile odorous fatty acids and their esters emitted from a typical textile plant, Juta a.s. (https://www.juta.eu/, Czech Republic). The effect of loading types on the biofilter performance was tested for 300 days (Table 1). Two loading patterns were applied. One of them included the loading variation by air flow rate (V g , in a range of 8-24 L min -1 at C in of 500 and 100 mg m -3 ) to simulate waste air with a low pollutant concentration yet causing a pungent odor). The second loading pattern was based on the variation of inlet concentration (C in , in a range of 100-1500 mg m -3 at V g of 3, 6 and 12 L min -1 ) to simulate heavily polluted air with relatively low flow rates. The biofiltration performance was evaluated using standard biofiltration parameters, elimination capacity, organic load, removal efficiency and empty bed residence time defined as follows:
Elimination capacity (EC):
Organic load (OL):
Removal efficiency (RE): Empty bed retention time (EBRT):
where C in and C out are the inlet and outlet n-butyl acetate concentrations in air (g m -3 ), respectively; V b is the packed bed volume (m 3 ) and Q is the air flow rate (m 3 h -1 ).
A mixed enriched culture taken from a biofilter treating a mixture of acetone and styrene, which was defined and successfully used previously [12] (link) was applied as an inoculum. The inoculum contained culturable isolated and identified bacteria, Pseudomonas sp., Bacillus sp., Arthrobacter sp., yeasts, Rhodococcus sp., Komagataella pastoris and fungus Fusarium solani. The selected mineral medium composition (BSM) allowed one to control pH (as a phosphate buffer) and supply the biofilm with water and mineral nutrients. 30 mL of this medium were added twice a day to each biofilter. It had the following composition (concentration given in g � L -1 ): KH 2 PO 4 (2.3), K 2 HPO 4 (2.9), (
