The application of a mulch biofilm barrier for surfactant enhanced polycyclic aromatic hydrocarbon bioremediation Youngwoo Seo, Woo-Hyung Lee, George Sorial, Paul L. Bishop * Department of Civil and Environmental Engineering, University of Cincinnati, 765 Baldwin Hall, PO Box 210071, Cincinnati, OH 45221-0071, USA Mulch biofilm barrier showed potential for surfactant enhanced bioremediation, and the presence of surfactant changed the structural composition of the biofilm. article info Article history: Received 26 March 2008 Received in revised form 24 July 2008 Accepted 26 July 2008 Keywords: Biofilm EPS Permeable reactive biobarrier PAH Surfactant abstract Lab scale mulch biofilm barriers were constructed and tested to evaluate their performance for pre- venting the migration of aqueous and surfactant solubilized PAHs. The spatial distribution of viable PAH degrader populations and resultant biofilm formation were also monitored to evaluate the performance of the biobarrier and the prolonged surfactant effect on the PAH degrading microorganism consortia in the biobarrier. Sorption and biodegradation of PAHs resulted in stable operation of the system for dis- solved phenanthrene and pyrene during 150 days of experimentation. The nonionic surfactant could increase the solubility of phenanthrene and pyrene significantly. However, the biobarrier itself couldn’t totally prevent the migration of micellar solubilized phenanthrene and pyrene. The presence of surfactant and the resultant highly increased phenanthrene or pyrene concentration didn’t appear to cause toxic effects on the attached biofilm in the biobarrier. However, the presence of surfactant did change the structural composition of the biofilm. Ó 2008 Elsevier Ltd. All rights reserved. 1. Introduction Hydrophobic organic compounds (HOC) are ubiquitous soil pollutants and cause world wide environmental problems. Among HOCs, polycyclic aromatic hydrocarbons (PAHs) have been of significant concern because they are known as major recalcitrant compounds and are also known to be carcinogenic to humans and other animals (Menzie et al.,1992; Harvey, 1996). PAHs are present in soils at many industrially contaminated sites including former manufactured gas plant (MGP) sites and creosote wood treatment facilities (Peters and Luthy, 1993). They have low solubility in water and are strongly bound to soil. However, their dissolution can contaminate large amounts of groundwater for long periods (Luthy et al., 1994). The bioremediation of polycyclic aromatic hydrocar- bons in soils is often limited by their low solubility and strong sorption to soil. In order to overcome the low solubility and strong sorption of PAHs to soil, one promising remediation technology is to solubilize and mobilize the contaminants by surfactant aided flushing (Peters and Luthy, 1993; Roy et al., 1997). Many researchers reported that surfactants could increase the solubility and mass transfer of hydrophobic organic compounds (Volkering et al., 1995, 1998; Barkay et al., 1999; Yeom et al., 1996). However, even though surfactants can increase the solubility of PAHs, surfactant aided soil flushing has shown other adverse effects. The main adverse effect is that previously immobile PAHs can begin to move and to spread through groundwater, due to their increased solubility and mobility (Moon et al., 2003). Therefore, solubilizing PAHs with surfactants can cause contamination of larger amounts of groundwater than normal treatment would have. Among in situ bioremediation technologies, the use of permeable reactive barriers within contaminated aquifers has grown as a way to prevent further migration of dissolved hydrocarbons from contaminated plumes with minimal maintenance costs (Kao et al., 2001). The permeable reactive barrier has been tested for various organic compounds, at both lab scale and full scale (Lamarche et al., 2001; Miller et al., 2001). Many different types of support material, including solid organic materials such as organic mulch, saw dust and peat moss, have commonly been used in bioremediation and bioretention systems in order to increase the efficiency of the permeable reac- tive biobarrier (Aziz et al., 1998; Yerushalmi et al., 1999; Scherer et al., 2000). In this research, lab scale mulch biofilm barriers were con- structed and tested to evaluate the applicability of a mulch biofilm biobarrier for preventing the migration of aqueous and surfactant * Corresponding author. Present address: Program Director for Environmental Implications of Emerging Technologies, Chemical, Biochemical, Environmental and Transport Systems Division (CBET), National Science Foundation, 4201 Wilson Boulevard, Arlington, VA 22230, USA. Tel.: þ1 513 556 3675; fax: þ1 513 556 2599. E-mail address: Paul.Bishop@UC.edu (P.L. Bishop). Contents lists available at ScienceDirect Environmental Pollution journal homepage: www.elsevier.com/locate/envpol 0269-7491/$ – see front matter Ó 2008 Elsevier Ltd. All rights reserved. doi:10.1016/j.envpol.2008.07.022 Environmental Pollution 157 (2009) 95–101