Review of the immobilized microbial cell systems for bioremediation of petroleum hydrocarbons polluted environments

Petroleum hydrocarbon contamination is widespread and has easily accumulated in various ecosystems due to hydrophobicity and limited bioavailability. Until now, the primary bioremediation techniques have used free cell (FC) cultures to remove these recalcitrant compounds from contaminated areas. The use of immobilized microbial cell systems is a promising technique, which has been recently applied in various environmental studies. The primary objective of this review is to give an overview of the key scientific aspects related to bioremediation of hydrocarbons using immobilized cell (IC), with a particular focus on the techniques to entrap the cells. The most effective cell immobilization technique was cell entrapping inside a porous matrix. This review also examines and compares the performance of ICs in biodegradation of petroleum hydrocarbons with those of FC systems. It has been observed that the biodegradation rate can be enhanced using immobilization technique, especially in harsh environments. Moreover, several advantages of using ICs compared to FCs are also discussed. For example, due to the easier separation, possible reutilization of microorganisms, and more tolerance to pH and temperature changes, ICs are generally preferred to FC systems. Finally, examples of some limitations of IC systems and new viewpoints in this field are presented.