In this link, a short presentation of legislation about odours nowadays can be downloaded (unfortunately in Spanish).
This subject is being discussed nowadays by several Autonomous Communities of Spain. It is necessary to have as reference the limits imposed by other countries with a much more elaborated legislation, as in several cases, there are not enough records to examine all the odour-generating activities.
In some occasions the doubt is presented through two questions: Is it necessary to develop an integral legislation about odours considering all activities? Or it is just convenient to regulate the activities with problems of this type? (e.g. Redering, animal farming, WWTPs, etc.?
In the first case, there should be a catalogue of activities potentially odour-generating in the way of the Spanish Decree 2414/1961 or from the existing in the Decree 833/1975. The construction of such a catalogue must count on the experience of people with experience in this field and should take into account the limits proposed in other international legislations.
In the second case, setting up a limit must be considered together with the activities involved in the regulation, as in some cases even the application of the BATs might not imply a reduction of the annoyance by odours. In addition, other important factors must be considered (land use, separation buffers, etc) when the purpose is to set a particularnumber of odour units.