A systematic approach to error isolation in computerized wastewater simulation models

Activated sludge models are used extensively in the study of wastewater tre atment processes. While various commercial implementations of these models are available, there are many people who need to code models themselves usi ng the simulation packages available to them, Quality assurance of such mod els is difficult. While benchmarking problems have been developed and are a vailable, the comparison of simulation data with that of commercial models leads only to the detection, not the isolation of errors. To identify the e rrors in the code is time-consuming. In this paper, we address the problem by developing a systematic and largel y automated approach to the isolation of coding errors. There are three ste ps: firstly, possible errors are classified according to their place in the model structure and a feature matrix is established for each class of erro rs. Secondly, an observer is designed to generate residuals, such that each class of errors imposes a subspace, spanned by its feature matrix, on the residuals. Finally. localising the residuals in a subspace isolates coding errors. The algorithm proved capable of rapidly and reliably isolating a va riety of single and simultaneous errors in a case study using the ASM 1 act ivated sludge model. In this paper a newly coded model was verified against a known implementation. The method is also applicable to simultaneous veri fication of any two independent implementations, hence is useful in commerc ial model development.