From BAT (best available technique) to BCAT (best combination of available techniques)

Technological choices are multi-dimensional and thus one needs a multidimensional methodology to identify best available techniques. Moreover, in the presence of environmental externalities generated by productive activities, ?best? available techniques should be best from Society's point of view, not only in terms of private interests. In this paper we develop a comprehensive modeling tool, based on methodologies appropriate to serve these two purposes, namely linear programming and internalization of external costs. We conclude that in this context there is in general not a single best available technique(BAT), but well a best combination of available techniques to be used (BCAT). We take a fictitious but plausible numerical example in the lime industry. For a hypothetical plant that has to meet a given demand, we build an original technical economic model within which two scenarios are considered: minimizing the private costs and minimizing the generalized costs (private costs plus external costs). In the first case, only the cheapest fuel is used in all kilns. But in the second case, where the environmental external costs are included, fuel switches occur and cleaner techniques are used. Extending the analysis to thechoice of kilns, we find that the socially best combination of available techniques (S-BCAT) is not a fixed one : it varies as a function of the external costs. We therefore trace in a single diagram the whole profile of these best techniques as successive solutions of our linear programs. We conclude by stressing that external cost internalization does influence not only the choice of techniques, but also their appropriate use. Moreover, local environmental conditions play a major role in that choice and in determining that use.