The process of hydrolysis of slowly biodegradable organics under different electron acceptor conditions has been pointed out as a weak part of Activated Sludge Model no. 2. Limited research input in this direction has led to lack of consensus and centered entire model uncertainties to this process. Here, we report consolidated results of our previous experimental studies on extracellular enzymatic hydrolysis. The main emphasis has been to understand general characteristics of extracellular hydrolytic enzymes in pure cultures and activated sludge. The experimental results suggest that the hydrolysis rates are not affected by the electron acceptor conditions for a single sludge steady state operated reactor. Since intracellular storage may influence correct interpretation of hydrolysis, it seems essential to evolve methods to study intracellular storage degradation and extracellular hydrolysis as two different processes. As the present wastewater characterization and model parameter estimation schemes do not consider storage aspects, this separation appears to be difficult. Hence, an experimental methodology is described to study hydrolysis and storage as two independent processes along with its limitations.

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