Aerobic biodegradation of an oxygenates mixture: ETBE, MTBE and TAME in an upflow fixed-bed reactor.

Aerobic degradation of ethyl tert-butyl ether (ETBE), Methyl tert-butyl ether (MTBE) and tert-amyl methyl ether (TAME), as tertiary-substrates, was studied in a continuous upflow fixed-bed reactor (UFBR) using an external oxygenator and sintered glass rings as biomass carriers. The UFBR has been shown to be an effective system for the simultaneous and continuous long-term degradation of the three-oxygenates mixture as sole source of carbon and energy. Therefore, the oxygenates feed concentration must be related in conjunction with the hydraulic retention time "HRT" and vice versa. The permissible feed concentration of both MTBE and TAME to achieve more than 99% removal efficiency is about 80 mg L-1 at a constant HRT of 24 h. The same performance can be obtained if the HRT kept at a value equal or above to 15 h for a feed concentration of about 80 mg L-1 of both MTBE and TAME. However, the ETBE removal efficiency was always greater than 99% whatever the ETBE concentration feed (between 10 and 100 mg L-1 at a constant HRT of 24 h) and the HRT (between 24 and 13 h at a constant concentration feed of about 80 mg L-1) tested in this study. The highest ETBE, MTBE and TAME removal rates achieved throughout the UFBR runs, with efficiency better than 99%, were 140 +/- 5, 132 +/- 2 and 135 +/- 2 mg L-1 d-1, respectively. No metabolic intermediates including tert-butyl alcohol (TBA), tert-butyl formate (TBF) and tert-amyl alcohol (TAA) were detected in the effluent during all the reactor runs. Furthermore, based on the chemical oxygen demand balance, all the removed oxygenates were completely metabolized. The results of this study suggest that the higher resistance to biodegradation exhibited by the MTBE and the TAME is probably due to the steric hindrance for the attacking enzyme(s); and the major limiting step to the oxygenate degradation maybe the accessibility and the cleavage of the ether bond, but not the assimilation of their major metabolites such as TBA, TBF and TAA. These results were concomitant with the batch tests using the reactor's immobilized biomass as inoculum.