Steady state and dynamic behaviors of a methane biofilter under periodic addition of ethanol vapors.

Ethanol was added to a methane (CH) biofilter with inorganic packing materials over three cycles based on increasing the gas flow rates from 3 to 6 and finally to 12 L min corresponding to empty bed residence times (EBRT) of 6, 3 and 1.5 min. The steady state performance of the CH biofilter was studied for CH inlet loads (ILs) of 33, 66 and 132 g m h prior and after each ethanol cycle. In addition, the steady state removal of a mixture of CH and ethanol for a CH/ethanol mass ratio of around 7.5 g g was evaluated over three cycles (EBRTs of 6, 3 and 1.5 min). In the absence of ethanol, the CH removal efficiency (RE) dropped from 35 to 7% due to an EBRT decrease from 6 to 1.5 min. In addition, the presence of ethanol resulted in a CH RE reduction at a constant EBRT in every cycle. The CH REs dropped from 35 to 29%, 17 to 13% and 7 to 0% for corresponding ethanol ILs of 4.5, 9 and 18 g m h over the cycles. Moreover, the periodic presence of ethanol in the CH biofilter allowed the study of transient behaviors of the biofilter during ethanol addition and the biofilter recovery after each cycle. The CH RE reduction as a result of ethanol addition in each cycle was instantaneous. However, the CH RE recovery after completion of ethanol addition took 10, 14 and 25 days for ethanol ILs of 4.5, 9 and 18 g m h respectively. The recovery time was related to the ethanol concentration in the leachate which were 1100 ± 200, 1100 ± 350 and 2500 ± 400 g m for corresponding ethanol ILs of 4.5, 9 and 18 g m h, respectively. Based on steady state and dynamic process conditions of the biofilter, the lowest gas flow rate of 3 L min (EBRT of 6 min) produced the best performance when both pollutants were present (CH IL of 33 g m h and ethanol IL of 4.5 g m h).