Content area
Full text
INTRODUCTION
1,4-Dioxane (C4H8O2, dioxane, ), which can be inhaled into the human body in the form of a gas, is a probable human carcinogen (IARC 1999). The World Health Organization established acceptable limits of dioxane in drinking water in 2003. Dioxane is used as a solvent and stabilizer, and is present in polyester manufacturing byproducts; it often exists in industrial wastewater, which makes it a potential source of environmental contamination (Zenker et al. 2003; Mohr et al. 2010). Dioxane is also used as a surfactant in foods, cosmetics, and detergents and, as a result, it ultimately contaminates domestic sewage (Black et al. 2001). Dioxane is highly soluble, mobile, and stable in water, and it is difficult to degrade biologically (Mohr et al. 2010). Because of these characteristics, dioxane is very difficult to remove from wastewater, which greatly increases the possibility of surface water and groundwater pollution (Sei et al. 2010).
To date, conventional wastewater treatment techniques (including coagulation-precipitation and carbon adsorption) remove dioxane inefficiently. Hydrogen peroxide, ozone, and/or ultraviolet light treatments remove dioxane efficiently but cause secondary environmental pollution (Suh & Mohseni 2004; Coleman et al. 2007). Bioremediation processes that are cost-effective and do not result in secondary pollution have become popular treatments for pollutants. Pseudonocardia, Mycobacterium, and Acinetobacter have been reported to directly and aerobically mineralize dioxane as a sole energy and carbon source (Parales et al. 1994; Kim et al. 2009; Sei et al. 2013; Huang et al. 2014). Another major way to degrade dioxane is via co-metabolism. Pseudonocardia sp. strains K1 and ENV478 were isolated from wastewater and tetrahydrofuran (THF, )-habituated cultures, and they were capable of degrading 1,4-dioxane after the THF was completely degraded (Kohlweyer et al. 2000; Vainberg et al. 2006). A high dioxane degradation rate occurs following bacterial growth in THF. Pseudonocardia sp. ENV478 mediated dioxane degradation resulted in the accumulation of the intermediate product 2-hydroxyethoxyacetic acid (HEAA) (Vainberg et al. 2006). It was speculated that the inability of strain ENV478 and some other THF-degrading bacteria to efficiently metabolize the intermediate product HEAA was the major reason for their failure to completely degrade dioxane. Flavobacterium was isolated from contaminated groundwater, and the rate of dioxane degradation increased with increasing THF concentrations (Sun et al. 2011). River, soil, activated sludge,...