Activated sludge physiology in relation to plant performance and control

A set of six bench scale sequencing batch reactors was designed specifically for the purposes of the experimentation on the activated sludge process for waste water treatment. The dissolved oxygen monitoring and control system allows for the measurements of on-line respiration rates using a simple closed loop ''on-off' control algorithm. The semi-batch nature of a sequencing batch reactor allows a detailed analysis of the dynamics of the process in a time dependent sequence which is representative of an idealised plug flow reactor. The effect of dynamic changes, such as the decline in free substrate availability, on the physiology of the microorganisms, can thus be monitored. Initial results from the on-line respirometry show a distinctive respiration rate profile which can be interpreted in relation to availability of readily biodegradable substrate, the oxidation process and nitrification.