Artificial intelligence techniques, including machine learning methods, and
statistical techniques have shown promising results as decision support to
ols, because of their capabilities of knowledge discovery, heuristic reason
ing and working with uncertain and qualitative information. Wastewater trea
tment plants are complex environmental processes that are difficult to mana
ge and control. This paper discusses the qualitative and quantitative perfo
rmance of several machine learning and statistical methods to discover know
ledge patterns in data. The methods are tested and compared on a wastewater
treatment data set. The methods used are: induction of decision trees, two
different techniques of rule induction and two memory-based learning metho
ds: instance-based learning and case-based learning. All the knowledge patt
erns discovered by the different methods are compared in terms of predictiv
e accuracy, the number of attributes and examples used, and the meaningful-
ness to domain experts.