The bugs eat the waste: what else is there to know? Changing professional hegemony in the design of sewage treatment plants.

New technologies may give rise to new professions, but existing professions may also try to acquire a role in the design of already existing artefacts that are designed by another profession. If they do so successfully, this may trigger technological change. A case study on the design of sewage treatment plants is presented, in which since the beginning of the 20th century microbiological and biotechnological researchers have tried to acquire a larger role at the cost of the traditionally involved civil engineers. The case is analysed with the help of Abbott's conceptual framework for professional competition. Two routes for professional competition that are typical for engineering, but that are not yet distinguished by Abbott, are identified and analysed: the development of new design parameters and the development of new design approaches.