PREFERENTIAL DEGRADATION OF ETHANOL IN

ALINE S. TEIXEIRA; DAIANA MORALES; MARIA DO CARMO RUARO PERALBA; RODRIGO J.S. JACQUES; FLAVIO A. O. CAMARGO; FATIMA M. BENTO

Natal

Simposio; II Brazilian Symposium on Petroleum Biotechnology; 2006

Benzene, tolueno and xylene isomers (BTEX) are the major components of gasoline and they cause many concerns mainly because of their high solubility in water and their acute toxicity and genotoxicity. The brazilian gasoline has 22-24% of ethanol that in case of a spill, a high aqueous ethanol concentration can facilitate the transfer of hydrocarbons into the aqueous phase, enhancing contaminants concentration in groundwater, a process called cosolvency. Under aerobic conditions, ethanol has been retarded BTX biodegradation. The preferential utilization of ethanol and the depletion of electron acceptors suggest that ethanol would have a negative effect on passive BTX bioremediation.  To have a better understanding of such effect was conducted a study in vitro with microorganisms isolated from soil contaminated with hydrocarbons (indigenous population) with gasoline as sole carbon source. BTX and ethanol were analyzed by HEADSPACE analisis in a gas chromatographi (Shimadzu 17A), according to the EPA 8015-B-96 methods. Microcosmos were prepared in 50 ml bottles with 10 ml of mineral medium with 1% of gasoline and sealed with aluminum crimps. After 3 weekly transfers the microorganisms were isolated. Various treatments including controls were conducted to discern biodegradation from volatilization losses. Growth curves were assayed and the results shows that benzene, toluene, xylene and ethanol removal in viable microcosmos, but not in sterile controls, provided evidence of biodegradation. In all cases, ethanol was preferentially utilized over all BTX compounds. One of the isolated tested (UFRGS2) shows that after 24 hours all ethanol had been completely degraded, and the degradation rates were to benzene, toluene and xylenes were 0,0 %, 39,9 % and 67,0 %, respectively. This suggests that, in bioremediation applications, the microbial population capable of degrading BTX would not fully express its catabolic potential while ethanol is present.