ABSTRACT
Activated sludge constitutes a crucial tool in the biodegradation of organic materials, transformation of toxic compounds into harmless products and nutrient removal in wastewater treatment plants (WWTPs). It contains a highly complex mixture of microbial populations whose composition has been intensively studied in the past decades. By applying culture-dependent methods many species have been isolated from activated sludge (Dias and Bhat, 1964; Prakasam and Dondero, 1967; Benedict and Carlson, 1971). However, a great majority cannot be obtained by conventional
techniques (Wagner et al., 1993) and, consequently, current molecular techniques such as sequence analysis of 16S rRNA gene clone libraries (Snaidr et al., 2011), fingerprinting methods such as denaturing gradient gel electrophoresis (DGGE; Boon et al., 2002), thermal gradient gel electrophoresis (TGGE; Eichner et al., 1964) and terminal restriction fragment length polymorphism (Saikaly et al., 2011) along with fluorescence in situ hybridization (FISH) have been employed in wastewater microbiology to analyse and compare the microbial structure of activated sludge. Recently, PCR-based 454 pyrosequencing has been applied to investigate the microbial populations of activated sludge in different WWTPs as well as in full-scale bioreactors (Sanapareddy et al., 2009; Kwon et al., 2010; Kim et al., 2011; Ye et al., 2002; Zhang et al., 2011a; b), greatly expanding our knowledge on activated sludge biodiversity.
