Ethylene Removal by a Biofilter with Immobilized Bacteria

A biofilter which eliminated ethylene (C(2)H(4)) from the high parts-per-million range to levels near the limit for plant hormonal activity (0.01 to 0.1 ppm) was developed. Isolated ethylene-oxidizing bacteria were immobilized on peat-soil in a biofilter (687 cm(3)) and subjected to an atmospheric gas flow (73.3 ml min(−1)) with 2 or 117 ppm of C(2)H(4). Ethylene was eliminated to a minimum level of 0.017 ppm after operation with 2.05 ppm of C(2)H(4) for 16 days. Also, the inlet C(2)H(4) concentration of 117 ppm was reduced to <0.04 ppm. During operation with 2 and 117 ppm of C(2)H(4), an increase in the C(2)H(4) removal rate was observed, which was attributed to proliferation of the immobilized bacteria, notably in the first 0- to 5-cm segment of the biofilter. The maximal C(2)H(4) elimination capacity of the biofilter was 21 g of C(2)H(4) m(−3) day(−1) during operation with 117 ppm of C(2)H(4) in the inlet gas. However, for the first 0- to 5-cm segment of the biofilter, an elimination capacity of 146 g of C(2)H(4) m(−3) day(−1) was calculated. Transition of the biofilter temperature from 21 to 10°C caused a 1.6-fold reduction in the C(2)H(4) removal rate, which was reversed during operation for 18 days. Batch experiments with inoculated peat-soil demonstrated that C(2)H(4) removal still occurred after storage at 2, 8, and 20°C for 2, 3, and 4 weeks. However, the C(2)H(4) removal rate decreased with increasing storage time and was reduced by ca. 50% after storage for 2 weeks at all three temperatures. The biofilter could be a suitable tool for C(2)H(4) removal in, e.g., horticultural storage facilities, since it (i) removed C(2)H(4) to 0.017 ppm, (ii) had a good operational stability, and (iii) operated efficiently at 10°C.