Methane biodegradation in a two-phase partition internal loop airlift reactor with gas recirculation

BACKGROUND: The potential of organic liquid solvents and solid polymers to enhance CH4 mass transfer was studied in a two-phase partition internal loop airlift reactor operated with gas recirculation under biotic and abiotic conditions. A preliminary screening of the most common liquid solvents (silicone oil 20 cSt, silicone oil 200 cSt and 2,2,4,4,6,8,8-heptametilnonane) and solid polymers (Kraton (R). G6157, Desmopan (R) DP9370A and Elvax (R) 880) resulted in the selection of silicone oil 200 cSt (S200) and Desmopan DP9370A (D9370) for further investigation based on their high affinity for CH4, biocompatibility and nonbiodegradability. RESULTS: Under abiotic conditions, the increase in gas recirculation from 0 to 1 vvm in the absence of a transfer vector increased the overall mass transfer coefficient for oxygen (k(L)a) by 195%. The presence of S200 and D9370 at 10% (v/v) under operation at 1 vvm of gas recirculation rate mediated an increase in kLa of 100% and 136%, respectively. Likewise, the increase in gas recirculation from 0 to 1 vvm in the absence of a transfer vector and in the presence of S200 during the continuous biodegradation of methane at 3% (v/v) and 7.3 min empty bed residence time resulted in increases in CH4 removal and CO2 production rates of 47% and 36%, respectively. Nevertheless, no significant enhancement in CH4 removal due to the presence of 10% of Desmopan or silicone oil was recorded under operation at 1 vvm. CONCLUSIONS: These results suggest that microbial activity rather than mass transport could be the limiting step in biological CH4 abatement in this system, contrary to that observed in previous studies with stirred tank reactors, where the organic phase addition increased methane biodegradation. (C) 2010 Society of Chemical Industry