The project described in this paper consists of two main stages: the development of a dedicated instrument enabling continuous simultaneous measures of industrial pollutants (e.g. metal ions: Ni2+, Cu2+, Zn2+, ...) and the design of a Real-time Expert System (RTES) which would provide better information and decision support so as to improve the supervision of waste-water treatment plants in real-time, applied to the surface treatment (electroplating) industries. The sensor is based on the principle of spectral absorption analysis. The real-time expert system is being developed using a commercial, industrially validated RTES-development software G2™ (by Gensym Corp.). A mixed knowledge-base is being implemented, comprising both types of knowledge: quantitative (e.g. theoretical knowledge issued from chemistry) and qualitative (i.e. operators' 'experience and know-how').