The influence of nutrients on floc physicochemical properties and structure in activated sludge processes

grantor: University of TorontoThe influence of nutrient levels (COD:N:P) on floc properties was studied using a laboratory sequencing batch reactor (SBR) system fed a glucose based synthetic waste. Floc physicochemical properties characterized included size settling velocity, density, porosity, and the compositions of extracellular polymeric substances (EPS). Floc structural analysis involved a minimal perturbation approach and correlative microscopy (CM). Various nutritional conditions were investigated: nutrient rich (Run 1), nutrient starved (Run 2), and nutrient limited (Run 3 and 4). Nutrient rich conditions (COD:N:P of 100:10:1, 100:5:2, 200:5:1) did not improve system performance and had no effect on floc sizes, settleability and floc morphology. Lack of N and P resulted in a deterioration of system performance. The deficiency in P resulted in an initial increase in floc sizes and settleability, but prolonged P-limited condition decreased settleability and density, although the floc sizes were still large and COD removal efficiency was good. The N-limited condition did not affect the system performance but affected floc settleability and size. Correlative microscopy (CM), including transmission electron microscopy (TEM), scanning confocal laser microscopy (SCLM) and conventional optical microscopy (COM), revealed heterogeneity in the EPS and distribution of the cellular and bioorganic components. The EPS in the flocs was shown to have differences in composition and spatial distribution. Total carbohydrates and protein were the major components of EPS. Under the P-starved condition, the concentrations of carbohydrates, protein and DNA of EPS increased. A similar trend was observed for the P-limited condition, but an increase in acidic polysaccharides was also detected. The N-limited condition resulted in a significant decrease of protein and DNA concentrations. The presence of Fe, S, and P within the EPS of flocs was detected by TEM and energy dispersive spectroscopy (EDS). (Abstract shortened by UMI.)M.A.Sc