An experimental study was undertaken to quantify the effects of intracellular storage polymers on the Oxygen Uptake Rate (OUR) profile and biomass yield coefficients for readily and slowly degradable substrates using a sludge from anaerobic-aerobic Sequencing Batch Reactor (SBR). Glucose and acetate were chosen as readily biodegradable substrates and soluble starch served as a model polymeric slowly degradable substrate. In case of acetate as substrate, PHA was the major storage polymer while polysaccharide acted as the main storage compound in case of glucose and starch. The accumulation of storage compounds even in the case of starch suggests that storage may be an integral part of the metabolic process for the sludge having storage capabilities. The maximum storage amounted to about 45%, 68% and 36% of total acetate, glucose and starch COD removed from bulk respectively. A new approach to calculate the true biomass yield coefficients based on exogenous OUR and considering intracellular storage is proposed. The relative independence of the calculated yield values to the amount of storage makes them suitable for application in growth kinetics. The calculated yield coefficients based on the proposed approach worked out to be 0.24–0.28, 0.58–0.50 and 0.64 for acetate, glucose and starch respectively and were significantly lower than the yield coefficients calculated based on conventional approach of not accounting storage. Further, the average degradation rate of intracellular glycogen were estimated to be 15 mg carbohydrate COD/g. MLSS. hr. with an average biomass yield of 0.45 mg biomass COD/mg carbohydrate COD.

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