METABOLIC TRANSFORMATIONS AND CHARACTERIZATION OF THE SLUDGE COMMUNITY IN AN ENHANCED BIOLOGICAL PHOSPHORUS REMOVAL SYSTEM

Enhanced biological phosphorus removal was performed in a continuous l aboratory-scale two-reactor system with sludge recirculation over a 75 -day period. Influent wastewater was a synthetic medium based on aceta te, and the sludge age was kept at 12 days. The adapted sludge stored poly-beta-hydroxyalkanoic acids (PHA) in the anaerobic reactor with a conversion ratio of 1.45 PHA/acetic acid (based on chemical O-2 demand : COD/COD) and gave ratio of a phosphate-P release to acetic acid upta ke of 0.51 P/CH3COOH (w/w). Fractionation of anaerobic and aerobic slu dges showed that the main part of phosphorus taken up, was eluted in t he trichloroacetic acid fraction indicating that it was polyphosphate. A total of 60% of the phosphorus in the aerobic sludge was solubilize d in the trichloroacetic acid fraction, whereas this fraction accounte d for only 32% of the phosphorus in the anaerobic sludge. Only 4% of t he total phosphorus in the aerobic sludge and 2% in the anaerobic slud ge was found in the EDTA fraction, indicating low amounts of metal-bou nd phosphates. Isolation on acetate-based agar medium showed that Acin etobacter strains were present in the sludge. However, a more complete analysis of the bacterial community of the sludge was obtained by cre ating a clone library based on the 16S rRNA gene. A total of 51 partia l clone sequences were phylogenetically evaluated. The predominating g roup was found in the high-(G + C) (mol%) gram-positive bacterial subp hylum (31% of the sequenced clones), while the gamma proteobacteria on ly constituted 9.8% of the clones.