Water Environment Federation (WEF)

Biodegradability of Alternative Oxygenates as a Sole Carbon Source or in the Presence of BTEX

The biodegradability of alkylate compounds in serum bottles was investigated as a sole carbon source or in the presence BTEX. The biomass was acclimated with 2,3-dimethyl pentane (2,3- DMP), 2,4-dimethyl pentane (2,4-DMP) and 2,2,4-trimethyl pentane (2,2,4-TMP) in porous potreactors. The alkylates (2,3-DMP, 2,4-DMP, and 2,2,4-TMP) were completely biodegraded in all the sets of experiments. When they were present with BTEX, alkylates degraded slower than when they were alone because BTEX inhibited the microbial utilization of alkylates. Throughout the experiments alkylates and BTEX concentrations did not change in the biologically inhibited controls.

Methyl t-butyl ether (MTBE) has been the most commonly used fuel oxygenate to reduce air pollution in the United States (USEPA 1998; Zein et al. 2004). However, because of its high water solubility and low affinity to soil particles, MTBE is often found in ground and surface water due to leaking underground storage tanks. It could potentially cause many health related problems by contaminating drinking water supplies (Johnson et al. 2000; Nihlen et al. 1998a; Nihlen et al. 1998b). Therefore, MTBE has been phased out in the U.S. and is being replaced by other oxygenates such as ethanol and alkylates.

The use of alkylates in gasoline will increase as MTBE is being phased out. Alkylates, highly branched alkanes, are much less water soluble than either MTBE or BTEX compounds. Therefore, they are likely to partition to the aquifer material and be much less mobile through the groundwater. Currently there is not much evidence of the aerobic and anaerobic biodegradation of alkylates. If they are biodegradable, they are probable to be more so under aerobic than anaerobic conditions. Alkylates, however, are likely to cause different types of environmental problems from those associated with MTBE. In groundwater they tend to adsorb to soil particles and biodegrade slowly. Biodegradation of gasoline by microflora from soil and groundwater of contaminated sites has been observed often (Jutras et al. 1997; Solano-Serena et al. 1999; Yerushalmi and Guiot 1998). Recent studies have revealed the ability of some bacterial and fungal cultures to aerobically biodegrade n-hexadecane, isooctane, and benzene (Jamroz 1996). Cyclohexane and 2,2,4-trimethyl pentane have been shown to be degraded by two mixed microbial communities selected from gasoline-polluted sites (Solano-Serena et al. 1998). In addition, a bacterial strain (strain IFP 2173) from a gasoline-polluted aquifer was also able to use 2,2,4-trimethyl pentane (isooctane) and 2,2-dimethyl pentane as a sole carbon and energy sources (Solano-Serena et al. 2000; Solano-Serena et al. 2004). The biodegradation of alkylates was performed in this study because there is evidence in literature to suggest that they are biodegradable.

The objective of this research was to evaluate the biodegradability and biodegradation kinetics of three alkylates, 2,3-DMP, 2,4-DMP and 2,2,4-TMP in the presence and absences of BTEX compounds under aerobic conditions in batch microcosms. Biomass capable of biodegrading these alkylates was harvested from a porous pot chemostat that was operated with these branched hydrocarbons as the sole carbon and energy sources.

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