Wastewater treatment bacteria show differential preference for colonizing natural biopolymers

Most reduced organic matter entering activated sludge systems is particulate (1-100-µm diameter) or colloidal (0.001-1-µm diameter), yet little is known about colonization of particulate organic matter by activated sludge bacteria. In this study, colonization of biopolymers (chitin, keratin, lignocellulose, lignin, and cellulose) by activated sludge bacteria was compared with colonization of glass beads in the presence and absence of regular nutrient amendment (acetate and ammonia). Scanning electron microscopy and quantitative PCR revealed chitin and cellulose were most readily colonized followed by lignin and lignocellulose, while keratin and glass beads were relatively resistant to colonization. Bacterial community profiles on particles compared to sludge confirmed that specific bacterial phylotypes preferentially colonize different biopolymers. Nitrifying bacteria proved adept at colonizing particles, achieving higher relative abundance on particles compared to bulk sludge. Denitrifying bacteria showed similar or lower relative abundance on particles compared to sludge. KEY POINTS: • Some activated sludge bacteria colonize natural biopolymers more readily than others. • Nitrifying bacteria are overrepresented in natural biopolymer biofilm communities. • Biopolymers in wastewater likely influence activated sludge community composition.