Active biomass in suspended growth systems exists as porous flocs. Since the rate of biodegradation is directly proportional to the substrate concentration at the microbial cell surface, the intrafloc substrate concentration profile will affect process kinetics. Data from previous experiments have indicated an improved effluent quality at increased SVI. Since the SVI parameter reflects biomass settleability rather than biodegradation kinetics, the experimental work was aimed at the relationship between SVI and mass transfer related properties. Four bench-scale units and one pilot plant were operated in parallel at nearly the same SRT with different anoxic:aerobic volume ratio, or mixed liquor recycle rate. Biomass samples at various SVI values were analyzed for specific surface area, effective diffusivity, and average floc size. The results have shown a direct linear relationship between the SVI and both the specific surface area and the effective diffusivity. These results suggested that changes in effective diffusivity were attributed to floc porosity. Using an existing model, effluent BOD under varying SVI were calculated, and the trend was similar to the results of previous study.

This content is only available as a PDF.
You do not currently have access to this content.