A statistical experiment design approach for optimizing biodegradation of weathered crude oil in coastal sediments Leila Mohajeri a , Hamidi Abdul Aziz a, * , Mohamed Hasnain Isa b , Mohammad Ali Zahed a a School of Civil Engineering, Universiti Sains Malaysia, 14300 Nibong Tebal, Penang, Malaysia b Civil Engineering Department, Universiti Teknologi PETRONAS, 31750 Tronoh, Perak, Malaysia article info Article history: Received 23 April 2009 Received in revised form 1 September 2009 Accepted 3 September 2009 Available online 20 September 2009 Keywords: Bioremediation Petroleum Nutrient Nitrogen Phosphorus abstract This work studied the bioremediation of weathered crude oil (WCO) in coastal sediment samples using central composite face centered design (CCFD) under response surface methodology (RSM). Initial oil con- centration, biomass, nitrogen and phosphorus concentrations were used as independent variables (fac- tors) and oil removal as dependent variable (response) in a 60 days trial. A statistically significant model for WCO removal was obtained. The coefficient of determination (R 2 = 0.9732) and probability value (P < 0.0001) demonstrated significance for the regression model. Numerical optimization based on desirability function were carried out for initial oil concentration of 2, 16 and 30 g per kg sediment and 83.13, 78.06 and 69.92 per cent removal were observed respectively, compare to 77.13, 74.17 and 69.87 per cent removal for un-optimized results. Ó 2009 Elsevier Ltd. All rights reserved. 1. Introduction Hydrocarbons present in the marine environment can originate from natural oil seepage and human activities includ- ing extraction, transportation, refining, storage, and utilization of petroleum (crude oil and natural gas) (Ebuehi et al., 2005; Kennish, 2001). Crude oil causes a variety of risks when released into the environment. It is physically, chemically and biologically harmful to soil because of the presence of many toxic compounds, such as polycyclic aromatic hydrocarbons, benzene and its substituted and cycloalkane rings, in relatively high con- centrations. The fate and effects of spilled crude oil and its prod- ucts in soils have already been the subject of several studies (Murakami et al., 2008; Ebuehi et al., 2005; Kulakow and Erick- son, 2000; Leahy and Colwell, 1990). Biodegradation of hydrocarbon compounds is one of the most important processes involved in the weathering and eventual re- moval of oil from the environment, particularly for its non-volatile components. Thus, potentially biodegradation can be used for recovery of sensitive areas such as contaminated shorelines, marshes, and wetlands. Bioremediation technologies have been developed for soils and coastal areas using the addition of nutrients and microbes (Lin and Mendelssohn, 2009; Lei et al., 2008; Joo et al., 2008; Greenwood et al., 2008). When a major oil spill occurs in freshwater and marine envi- ronments, amount of carbon increase and the availability of nitrogen and phosphorus usually becomes the limiting factor for oil degradation (Leahy and Colwell, 1990). Huang et al. (2008), Borresen and Rike (2007), and Boopathy (2000) deter- mined optimum nutrient supplement levels at laboratory incuba- tion experiments. Ongoing research and development seeking to improve meth- ods by minimizing the number of experiments provide informa- tion about the direct additive effects of the study variables and interaction effects using design of experiment methods. Recently, this statistical technique has been successfully applied in many fields (Huang et al., 2008; Rigas et al., 2007; Pala et al., 2006; Ahmadi et al., 2005). The use of the technique enables selection of the best materials, equipment and process condi- tions for focusing on the correct variables and ranges for further study. The statistical experiment designs most widely used in optimi- zation experiments are termed response surface designs (Mohan et al., 2009; Da Silva et al., 2009; Huang et al., 2008; Rigas et al., 2007; Pala et al., 2006; Ahmadi et al., 2005). These designs provide information about direct effects, pairwise interaction ef- fects and curvilinear variable effects. In this experiment coastal sediments artificially polluted with weathered crude oil (WCO) were studied. The application of central composite face centered design (CCFD) under response surface methodology (RSM) assisted in both modeling and optimization of the weathered crude oil biodegradation. 0960-8524/$ - see front matter Ó 2009 Elsevier Ltd. All rights reserved. doi:10.1016/j.biortech.2009.09.013 * Corresponding author. Tel.: +60 4 5996203; fax: +60 4 5941009. E-mail address: cehamidi@eng.usm.my (H.A. Aziz). Bioresource Technology 101 (2010) 893–900 Contents lists available at ScienceDirect Bioresource Technology journal homepage: www.elsevier.com/locate/biortech