Biological sludge stabilisation Part 1: Kinetics of aerobic sludge digestion

Abstract

The Marais and Ekama (1976) activated sludge model describes inter alia the aerobic digestion process as a first order process with respect to the active (live) sludge concentration. Since the active sludge concentration cannot be measured directly, the decay constant of the first order process relationships can only be calculated after deriving expressions linking changes of measurable parameters to the change of active sludge. Relationships are derived between the change of the active sludge concentration and of four parameters that can be determined by simple methods: Oxygen uptake rate (OUR), volatile suspended solids (VSS) concentration, nitrate concentration and alkalinity. The aerobic batch digester is particularly useful to evaluate the validity of the model and the expression linking change of the four parameters to active sludge decay. From observations of aerobic batch digesters it is concluded that the changes of the four parameters all lead to the same value of the decay constant.

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