DIFFUSIONAL LIMITATION AND PROCESS KINETICS IN SUSPENDED GROWTH SYSTEMS

`Active biomass in suspended growth systems exists as porous flocs. Si nce the rate of biodegradation is directly proportional to the substra te concentration at the microbial cell surface, the intrafloc substrat e concentration profile will affect process kinetics. Data from previo us experiments have indicated an improved effluent quality at increase d SVI. Since the SVI parameter reflects biomass settleability rather t han biodegradation kinetics, the experimental work was aimed at the re lationship between SVI and mass transfer related properties. Four benc h-scale units and one pilot plant were operated in parallel at nearly the same SRT with different anoxic:aerobic volume ratio, or mixed liqu or recycle rate. Biomass samples at various SVI values were analyzed f or 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. Thes e results suggested that changes in effective diffusivity were attribu ted to flee porosity. Using an existing model, effluent BOD under vary ing SVI were calculated, and the trend was similar to the results of p revious study. Copyright (C) 1996 IAWQ.