Biofiltration of methane from cow barns: Effects of climatic conditions and packing bed media acclimatization

Abstract The performance of biofiltration to mitigate CH 4 emissions from cow barns was investigated in the laboratory using two flow-through columns constructed with an acclimatized packed bed media composed of inexpensive materials and readily available in an agricultural context. The biofilters were fed with artificial exhaust gas at a constant rate of 0.036 m 3  h −1 and low inlet CH 4 concentration (0.22 g m −3  = 300 ppm). The empty-bed residence time (EBRT) was equal to 0.21 h. Additionally, in order to simulate temperature changes under natural conditions and determine the influence of such cycles on CH 4 removal efficiency, the upper part of the biofilters were submitted to temperature oscillations over time. The maximum oxidation rate (1.68 μg CH4 g dw −1 h −1 ) was obtained with the commercial compost mixed with straw. Accordingly, it was considered as packing bed media for the biofilters. The CH 4 removal efficiency was affected by the temperature prevailing within the biofilters, by the way in which the cooling-warming cycles were applied and by the acclimatization process. The shorter the cooling-warming cycles, the more oxidation rates varied. With longer cycles, CH 4 removal rates stabilized and CH 4 removal efficiencies attained nearly 100% in both biofilters, and remained at this level for more than 100 days, irrespective of the temperature at the top of the biofilter, which was – at times – adverse for microbiological activity. The first order rate constant for CH 4 oxidation kinetics of the entire system was estimated at 15 h −1 . If such rate could be transposed to real field conditions in Canada, home to nearly 945,000 dairy cows, biofiltration may be applied to efficiently abate between 2 × 10 6 and 3 × 10 6  t yr −1 of CO 2 equivalent (depending on how estimates are performed) from bovine enteric fermentation alone.