Characterization of extracellular polymeric substances in rotating biological contactors and activated sludge flocs

Extracellular polymeric substances (EPS) from biofilms of a rotating biological contactor (RBC) system and from activated sludge flocs were extracted using ultrasound and a cation exchange resin. In both wastewater treatment systems, the EPS matrix was mainly constituted of proteins, humic-like substances and polysaccharides, although other components - DNA and uronic-like substances- were also present. The composition of the biofilm EPS was different in the successive RBC wastewater treatment stages: protein had its highest concentration in the first RBC unit, while humic substances and polysaccharides in the third RBC. Significant differences between biofilm and sludge floc EPS were also reported. The amount of proteins was 3.5 times higher for RBC biofilms than for sludge flocs, and quantities of humic substances and polysaccharides extracted from biofilms were twice as high than in sludges. Moreover, biofilm exopolymers were two times more hydrophobic than those of sludge flocs. Implications of wastewater chemistry and microbial growth strategies into EPS composition and properties are suggested.