Ethylene removal at low temperatures under biofilter and batch conditions

Removal of the plant hormone ethylene (C(2)H(4)) is often required by horticultural storage facilities, which are operated at temperatures below 10 degrees C. The aim of this study was to demonstrate an efficient, biological C(2)H(4) removal under such low-temperature conditions. Feat-soil, acclimated to degradation of C(2)H(4), was packed in a biofilter (687 cm(3)) and subjected to an airflow (similar to 73 mi min(-1)) with 2 ppm (mu l liter(-1)) C(2)H(4). The C(2)H(4) removal efficiencies achieved at 20, 10, and 5 degrees C, respectively, were 99.0, 98.8, and 98.4%. This corresponded to C(2)H(4) levels of 0.022 to 0.032 ppm in the biofilter outlet air. At 2 degrees C, the average C(2)H(4) removal efficiency dropped to 83%. The detailed temperature response of C(2)H(4) removal was tested under batch conditions by incubation of l-g soil samples in a temperature gradient ranging from 0 to 29 degrees C with increments of 1 degrees C. The C(2)H(4) removal rate was highest at 26 degrees C (0.85 mu g of C(2)H(4) g [dry weight](-1) h(-1)), but remained at levels of 0.14 to 0.28 mu g of C(2)H(4) g (dry weight)(-1) h(-1) at 0 to 10 degrees C. At 35 to 40 degrees C, the C(2)H(4) removal rate was negligible (0.02 to 0.06 mu g of C(2)H(4) g [dry weight](-1) h(-1)). The Q(10) (i.e., the ratio of rates 10 degrees C apart) for C(2)H(4) removal was 1.9 for the interval 0 to 10 degrees C. In conclusion, the present results demonstrated microbial C(2)H(4) removal, which proceeded at 0 to 2 degrees C and produced a moderately psychrophilic temperature response.