Biodegradation kinetics of gasoline under nitrate reducing conditions in a continuous-upflow biofilm reactor

摘要

Gasoline is a complex mixture of more than 150 chemicals that does not occur naturally in the environment and is produced from petroleum in the refining process. To enhance cleaner fuels and reduce toxic air emissions, the United States 1990 Clean Air Act Amendments (CAA) established the Federal Reformulated Gasoline (RFG) program. Under this program, the oxygen content of RFG should not be less than 2% by weight (CAA, 1990). Oxygenates make gasoline burn cleaner and more efficiently while enhancing octane quality and reducing exhaust emissions. To achieve the required level of oxygen for gasoline sold in carbon monoxide (CO) nonattainment areas the addition of about 15% methyl tertiary-butyl ether (MTBE) or about 7.5% ethanol (by volume) was required (NSTC, 1997). As a result, MTBE was released into the environment and some groundwater sites became contaminated in the U.S. (Squillace et al., 1996), Germany (Kolb and Puttmann, 2006), and elsewhere (Hsieh et al., 2006). To protect human health effects from MTBE exposure, MTBE drinking water health advisory levels for odor and taste were set at 20 and 40 ug/L, respectively by the EPA (USEPA, 2004). Current trends show MTBE phasing out and eventual replacement by ethanol in unleaded gasoline, which in turn, might bring new challenges. Therefore, efforts to restore gasoline polluted drinking water sources require the development of new and more effective technologies to treat contaminated sites, including groundwater.