The hydrolysis rates under anaerobic, anoxic and aerobic conditions are studied by using starch as a model organic substrate representing the slowly biodegradable COD. An analytical method, the starch-iodine complex formation method, was introduced to distinguish the polymer starch and its hydrolysis products, and it was applied to estimate the hydrolysis rates in an activated sludge mixed culture, two bacterial pure cultures (Bacillus amyloliquefaciens and Aeromonas hydrophila) or a pure enzyme (α-amylase) system. The rate of starch hydrolysis was found to be independent of the electron acceptor conditions. The starch hydrolysis rate constant of the activated sludge was not affected by the biomass concentration, which indicates that the starch hydrolysis in the activated sludge process follows surface limited adsorption reaction kinetics.

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