Research review paper Extracellular biopolymeric flocculants Recent trends and biotechnological importance H. Salehizadeh, S.A. Shojaosadati* Biotechnology Group, Chemical Engineering Department, Tarbiat Modarres University, P.O. Box 14155-4838, Tehran, Iran Abstract Many microorganisms secrete extracellular biopolymeric flocculants (EBFs) in the culture broth. This work reviews the development of EBF research and applications. Aspects discussed include a comparison of the chemical and biological flocculating agents, isolation of EBF-producing microorganisms, culture conditions, mechanisms of flocculation, the chemical structure of EBFs, and the role of physicochemical factors in the flocculating activity. D 2001 Elsevier Science Inc. All rights reserved. Keywords: Bioflocculant; Biopolymer; Flocculant; Flocculation 1. Introduction Flocculating agents are widely used in industrial processes including wastewater treatment, downstream processing, and food and fermentation processes (Gutcho, 1977; Nakamura et al., 1976a; Cumming et al., 1996; Vanhoric and Moens, 1983; Dearfield and Ambermathy, 1988; Pasteur, 1876; Bordet, 1899; Butterfield, 1935; Mckinney, 1956; Misra, 1993; Bender et al., 1994; Yokoi et al., 1996a; Kurane et al., 1966; Kakii et al., 1986; Morgan et al., 1990; Hantula and Bamford, 1991a,b; Guirand, 1992; Dube, 1992; Sousa et al., 1992; Kim, 1993; Suh et al., 1997; Seo, 1993; Levy et al., 1992; Bar-Or and Shilo, 1987; Fumio, 1991; Tong et al., 1999; Huang, 1990; Salehizadeh et al., 1998, 2000; Tenny and Stumm, 1965; Tenny and Verhoff, 1973; Busch and Stumm, 1968). The flocculants used can be classified into three 0734-9750/01/$ – see front matter D 2001 Elsevier Science Inc. All rights reserved. PII:S0734-9750(01)00071-4 * Corresponding author. Fax: +98-21-800-6544. E-mail address: shoja_sa@modares.ac.ir (S.A. Shojaosadati). Biotechnology Advances 19 (2001) 371 – 385