A model was developed to describe hydrolysis in a moving bed with polyurethane foam carriers under anoxic conditions. It is formulated as a two-box model and structured into bulk and carrier compartments linked by mass transfer processes for solutes and particles. The biological processes consist of the anoxic growth and decay of heterotrophic organisms and hydrolysis of the slowly biodegradable substrate. Kinetic and stoichiometric parameters are taken from Activated Sludge Model No. 2 (Henze et al., 1995). Parameter estimations based on 24 batch experiments resulted in anoxic hydrolysis rates of 3.9 d−1 (at 20°C) and 2.6 d−1 (at 10°C).
The mass transfer coefficient for solutes was determined from the mixing of an inert tracer to be 0.3 m d−1. Measurements of the enzymatic activity of α-, β-glucosidase and esterases confirmed that 90% of the activity involves the carriers. In conjunction with the finding that the absorption capacity of the carriers for slowly biodegradable substrate is high, it can be concluded that the hydrolysis takes place principally within the carriers.