Multivariable control of nutrient-removing activated sludge systems

The aim of this paper is to evaluate several multivariable model-based control algorithms for controlling nitrogen removal in activated sludge processes. We contend that the control of nutrient removal in activated sludge systems is a multivariable control problem, rather than a multiloop problem. The work is a simulation study of a predenitrification activated sludge plant. Several model-based controllers are evaluated and compared against a base-case and multiloop controller. We introduce a quantitative measure to aid in controller evaluation. Model based control algorithms are shown to be able to provide tight control of N removal, thereby offering significant benefits in terms of deferred capital expenditure. This is in return for increased operating costs.