Immobilization of microbial cells for the biotreatment of wastewater: A review

Industrial wastewater often contains different complex impurities that are hazardous to the environment and human health, making wastewater treatment a necessity prior to its disposal. This review focuses on cell immobilization in the biological wastewater treatment, in which microorganisms are utilized for the biodegradation and removal of different types of contaminants, depending on the type of contaminat. Cell immobilization provides the ability to successfully limit the mobility of the cells using synthetic or natural polymers, which can then be used as biocatalysts instead of free cells. We provide a comprehensive evaluation of major cells immobilization aspects, starting from the definition of the technology and focusing on a critical and technical analysis of the currently used immobilization techniques including adsorption, covalent binding, entrapment and encapsulation. Biological water treatment systems using immobilized cells have the potential to be utilized in the degradation of various types of wastewater contaminants. This resulted in remarkable advances in the immobilization techniques, used materials, and properties of immobilized systems. Cell immobilization techniques are becoming well developed, new techniques are being studied by researchers, and the trend of advances in this area is expected to continue increasing in the coming years. Studies proved that immobilization is an effective and promising technique to enhance biological wastewater treatment processes. Immobilized cells could increase the removal efficiency of water contaminants, particularly nutrients, by more than 60%. In this review, the main factors in the development of immobilized cells are highlighted, starting from the selection of immobilization support and providing a detailed description of the immobilization techniques. The application of cells immobilization for different wastewater treatment processes is illustrated. Different examples of wastewater biotreatment are presented, including refractory organics wastewater, wastewater containing heavy metal ions, nitrogen and phosphorous wastewater as well as the removal of dye and color in textile industry wastewater. The review ends with a brief overview of future perspectives of research on cells immobilization.