[Formation and reaction mechanism of simultaneous nitrogen and phosphorus removal by aerobic granular sludge]

Aerobic granular sludge (AGS) for simultaneous nitrogen and phosphorus removal (SNPR) was cultivated and studied in two lab-scale sequencing batch reactors (named as A & B) treating real domestic wastewater, additional carbon (sodium propionate and sodium acetate for A, glucose for B) was added to make the ratio of COD:N:P as 360:60:6, good SNPR was achieved at normal (18-27 degrees C) and low temperature (9-13 degrees C). The microbial community composition and distribution, distribution of cells and extracellular polymeric substances (EPS) and morphologies of the AGS were investigated using fluorescence in situ hybridization (FISH), in situ fluorescent staining and scanning electron microscope (SEM), respectively. FISH results showed that ammonium-oxidizing bacteria comprised 12% of all the bacteria and were mainly located at the outer parts of the granules; phosphates accumulating organisms comprised 40% of all the bacteria and were mainly located in the inner parts of the granules. Nitrification was the rate controlling step; denitrifying phosphate accumulating organisms inside the granular sludge might be responsible for denitrification in the aerobic phase, which enabled effective SNPR. Live/dead fluorescent staining results showed that dead cells were distributed throughout the granules and live cells were principally distribution of polysaccharide (including alpha-mannopyranosyl, alpha-glucopyranosyl sugars and beta-D-glucopyranose polysaccharides) of EPS in AGS were influenced by different carbon sources, but the contents and distributions of protein and lipids were not, the contents of protein was the largest. Polysaccharide was responsible for the formation and maintenance of aerobic granular sludge. SEM results showed that bacilli and cocci were the main bacteria in the granules of A and B, respectively. Carbon sources affected the bacteria type and the SNPR efficiency, sodium propionate and sodium acetate were better than glucose.