Naphthalene degradation in the presence of natural–synthetic surfactants mixture by mixed bacterial cultures K. Jagajjanani Rao, Rajib Ghosh Chaudhuri, Santanu Paria * Interfaces and Nanomaterials Laboratory, Department of Chemical Engineering, National Institute of Technology, Rourkela 769 008, Orissa, India Introduction Polycyclic aromatic hydrocarbons (PAHs) are considered as hazardous pollutants because of their toxicity to human health and ecosystems [1,2]. Bioremediation is an available cheaper technol- ogy, in which microorganisms such as bacteria and fungi degrade organic contaminants (e.g., PAHs) into less toxic compounds [3,4]. Despite the above mentioned advantages, this technology suffers from main bottlenecking of low solubility and/or availability of hydrophobic organic contaminants (e.g., PAHs) in aqueous media, which in turn leads them unavailable to microorganism’s [5]. The bioavailability of PAHs can be enhanced by increasing solubility so that the microorganisms can degrade them. Published studies show that the rate of biodegradation of PAHs by microorganisms is quite low unless some favorable conditions are maintained, such as acclimatization/enrichments with specific ion, low PAH concen- trations and higher exposure times [6–9]. The use of solubilizing agents such as surfactants can enhance the solubility of PAHs, which in turn directly enhance the mass transfer rate and bio-availability. Many studies employing single and mixed surfactants showed their enhanced remediation potential in solubilizing and mobilizing organic contaminants such as PAHs [10–13]. However, when synthetic surfactants are used as solubilizing agents, in many cases their presences in soil or water can also show adverse effect on environment [14,15]. So, biosurfactants are appeared as the most possible alternative to that of synthetic ones because of their easy degradability and availability from the renewable sources [16]. In general, biosur- factants have microbial and plant based origin. However, the use of biosurfactants of microbial origin is limited because the lack of large scale industrial production due to high recovery or separation costs and some possess antimicrobial properties too [17–19]. In recent times, the use of eco-friendly surfactants from renewable plant sources for soil and water remediation is of great importance. Only a few studies were available with reference to the application of plant-based natural surfactants from Sapindus mukorossi for soil remediation [19–21]. Till date, most of the research papers highlight on the effect of synthetic and bio-surfactants on the bioavailability of PAHs toward single and mixed cultures [11,22–24]. In some studies it has been shown that mixed cultures are advantageous over the single one [2,4]. So, in the present study we focused on the degradation of a simple PAH such as naphthalene in the presence of plant–synthetic mixed surfactant systems. This work is an extension of our Journal of Environmental Chemical Engineering 2 (2014) 826–831 A R T I C L E I N F O Article history: Received 22 July 2013 Received in revised form 14 January 2014 Accepted 14 February 2014 Keywords: Naphthalene biodegradation Reetha Natural–synthetic mixed surfactant Degradation rate constant Bioremediation A B S T R A C T Biosurfactants are the most probable future candidates to substitute the synthetic surfactants in the area of applied surfactants research. Herein we focused on the natural plant based surfactant (Reetha) extracted from the pod of Sapindus mukorossi and its substitution potential with synthetic surfactants (TX-100, CTAB, and SDBS). Mixture of Reetha and synthetic surfactants was tested for the biodegradation of naphthalene. The biodegradation efficiency of surfactants against two mixed bacterial cultures viz., defined or known culture (KC) and mining waste water culture (WWC) was investigated. Addition of Reetha in the presence of ionic surfactants has increased the degradation efficiency of naphthalene. Degradation rate constants (K) and zeta potential assessments revealed that WWC has more potential than KC with surfactant mixtures (especially CTAB-Reetha). The highest degradation potential (K value = 0.31) was identified with WWC having 0.5 mol fraction of Reetha in CTAB-Reetha combination. The results suggested that the use of Reetha in combination with ionic surfactants has an enormous potential to make the biodegradation process more eco-friendly and economical by decreasing the surfactant cost. ß 2014 Elsevier Ltd. All rights reserved. * Corresponding author. Tel.: +91 6612462262; fax: +91 661 246 2999. E-mail addresses: santanuparia@yahoo.com, sparia@nitrkl.ac.in (S. Paria). Contents lists available at ScienceDirect Journal of Environmental Chemical Engineering jou r n al h o mep ag e: w ww .elsevier .co m /loc ate/jec e http://dx.doi.org/10.1016/j.jece.2014.02.011 2213-3437/ß 2014 Elsevier Ltd. All rights reserved.