Prolonged operation of a methane biofilter from acclimation to failure stage.

Global warming needs urgent action to reduce major greenhouse gas emissions including methane (CH 4 ). Bio-oxidation of dilute CH 4 emissions in packed-bed bioreactors such as biofilters has been carried out over the recent years at laboratory and large scales. However, a big challenge is to keep CH 4 biofilters running for a long period of time of the order of years. In this study, a packed-bed lab-scale bioreactor with a specialized inorganic-based filter bed successfully operated over four years for CH 4 elimination. The inoculation of the bioreactor was the active leachate of another CH 4 biofilter which resulted in a fast acclimation and removal efficiency (RE) reached 80% after seven weeks of operation for CH 4 inlet concentrations ranging from 700 to 800 ppmv and an empty bed residence time (EBRT) of 6 min. During four years of operation, the bioreactor often recorded REs higher than 65% for inlet concentrations in the range of 1900 to 2200 ppmv and an EBRT of 6 min. The rate and interval of the nutrient supply played an important role in maintaining the bioreactor's high performance over the long operation. Forced shutdowns were unavoidable during the 4-year operation and the bioreactor fully tolerated them with a partial recovery within one week and a progressive recovery over time. At the end, the bioreactor's filter bed started to deteriorate due to a long shutdown of twelve weeks and the extended operation of four years when the RE dropped to below 8% with no sign of returning to its earlier performance.