Oil pollution generated from both natural and anthropogenic sources could cause significant damages to the environment, due to the toxicity of some of its constituents. Microorganisms have been used for oil pollution bioremediation. However, compared to free microorganisms, immobilized microorganisms possess several advantages, including high metabolic activity rates, strong resistance to toxic chemicals and effective resistance to washing away. Obviously, it is important to obtain high efficiency immobilized cells. Therefore, optimization of immobilization parameters demand critical understanding and control in practical applications. In this study, a central composite design (CCD) was employed to optimize the immobilization of Dietzia cercidiphylli strain X10 onto modified zeolite. The independent variables were fixed time(X1), initial cell age(X2) and carrier dosing quantity(X3). The optimum condition with higher percentage of oil removal was chosen from a predicted condition proposed by CCD design with a real model presented as: Oil removalY(%)=42.54+0.0675X1+0.27875X2+0.07625X3–1.0175X1X1–0.3025X1X2+0.1875X1X3–1.45X2X2 + 0.335X2X3 – 1.065X3X3. This equation clearly suggested that there was a strong interaction effect between the variables and the interaction effect was accounted using response surface methodology. Surface plots of oil degradation rates over independent variables were shown in Fig.1. The response surface showed maximum activity at the optimal points determined below, suggesting that the optimal conditions determined were correct. It is also clear that the optimal point obtained from the model is clearly a saddle point, which lies within the selected range of the parameters. According to quadratic equation and mathematical calculation, the optimal conditions of fixed time, initial cell age and carrier dosing quantity were 75.5h of cell age, 1.7g carrier/ 0.5g dry cell with 75h of fixed time. Under the optimal conditions of variables, a maximum degradation rate of 42.56% was obtained from the quadratic equation. The experimental values are in good agreement with predicted values within +0.05 to +0.88% error. This suggested that response surface methodology can be successfully used to optimize the immobilization parameters affecting the oil degradation.

Process optimization studies of oil degrading Dietzia cercidiphylli strain X10 immobilization onto modified zeolite using response surface methodology

251st National Meeting (2016)

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