Ethylene removal by a biofilter with immobilized bacteria.

A biofilter which eliminated ethylene (C2H4) 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 cm3) and subjected to an atmospheric gas flow (73.3 ml min-1) with 2 or 117 ppm of C2H4. Ethylene was eliminated to a minimum level of 0.017 ppm after operation with 2.05 ppm of C2H4 for 16 days. Also, the inlet C2H4 concentration of 117 ppm was reduced to <0.04 ppm. During operation with 2 and 117 ppm of C2H4, an increase in the C2H4 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 C2H4 elimination capacity of the biofilter was 21 g of C2H4 m-3 day-1 during operation with 117 ppm of C2H4 in the inlet gas. However, for the first 0- to 5-cm segment of the biofilter, an elimination capacity of 146 g of C2H4 m-3 day-1 was calculated. Transition of the biofilter temperature from 21 to 10 degreesC caused a 1.6-fold reduction in the C2H4 removal rate, which was reversed during operation for 18 days. Batch experiments with inoculated peat-soil demonstrated that C2H4 removal still occurred after storage at 2, 8, and 20 degreesC for 2, 3, and 4 weeks. However, the C2H4 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 C2H4 removal in, e.g., horticultural storage facilities, since it (i) removed C2H4 to 0.017 ppm, (ii) had a good operational stability, and (iii) operated efficiently at 10 degreesC.