MINI-REVIEW Advances in biofilm reactors for production of value-added products Kuan-Chen Cheng & Ali Demirci & Jeffrey M. Catchmark Received: 29 January 2010 / Revised: 13 April 2010 / Accepted: 13 April 2010 / Published online: 2 May 2010 # Springer-Verlag 2010 Abstract Biofilms are defined as microbial cell layers, which are irreversibly or reversibly attached on solid surfaces. These attached cells are embedded in a self-produced exopolysac- charide matrix, and exhibit different growth and bioactivity compared with suspended cells. With their high biomass density, stability, and potential for long-term fermentation, biofilm reactors are employed for the fermentation and bioconversion, which need large amount of biomass. During the past decade, biofilm reactors have been successfully applied for production of many value-added products. This review article summarizes the applications of biofilm reactors with different novel designs. Advantages and concerns using biofilm reactors, potential uses for industrial-scale production, and further investigation needs are discussed. Keywords Biofilm . Biofilm reactors . Plastic-composite supports . Cell immobilization . Fermentation Introduction The first biofilms were discovered by van Leeuwenhoek on the surface of teeth when using microscopes. Biofilm is defined as naturally occurring microbial cell layers, which are irreversibly attached to solid surfaces. These microbial cells are embedded in an exopolysaccharide matrix and exhibit different growth and bioactivity compared to suspended cells. Biofilms have drawn increasing attention due to many detrimental effects on human health, such as infections on prosthetic implants (Bayston 2000) and in patients with cystic fibrosis (Jackson et al. 2003). It also causes biofouling in engineered materials and systems (Gassey and Bryers 2000; Wirtanen et al. 2000; Chmielewski and Frank 2003; Patching and Fleming 2003). However, biofilm can be used in many applications, such as water purification and wastewater treatment (Lazarova and Manem 2000; O'Flaherty 2003), bioremediation (Von Canstein et al. 2002), removal of toxic pollutants (Ebihara and Bishop 2002; Jin et al. 2003), and enhanced production of value-added fermentation products (Demirci et al. 2007). Therefore, the number of publications dealing with either the problems caused by biofilm or the applications benefited from biofilms is increasing. Unlike the biofilm reactor applications for wastewater treatment and bioremediation, which have been intensively studied, biofilm reactors which are implemented to produce value-added products are still remained in bench-scale or pilot-scale during the past decades. In spite of this, biofilm reactors have been proven to enhance productions of value- added products, such as bioethanol, organic acids, enzymes, antibiotics, and polysaccharides as they can generate increased volumetric productivity rates by maintaining high biomass concentration in the bioreactors (Demirci et al. 2007). With their exceptional stability and lower nutrient requirement, biofilm reactors demonstrate their potential for the development of continuous fermentation and the applica- tions in the large-scale production of value-added products. In this review article, a brief background of biofilm formation and structure and its recent applications are presented. The advantages and concerns of the applications of biofilm reactors will be discussed. K.-C. Cheng : A. Demirci (*) : J. M. Catchmark Department of Agricultural and Biological Engineering, The Pennsylvania State University, University Park, PA 16802, USA e-mail: demirci@psu.edu A. Demirci The Huck Institutes of Life Sciences, The Pennsylvania State University, University Park, PA 16802, USA Appl Microbiol Biotechnol (2010) 87:445–456 DOI 10.1007/s00253-010-2622-3