In 2015, The Brussels Institute for Research and Innovation (Innoviris) launched an innovative policy in Europe, inviting Brussels research consortia to propose participatoryaction research (PAR) projects. PHOSPHORE and BRUSSEAU worked for three years in and on Brussels socio-technical systems, respectively on biowaste and water management. These research projects revealed many institutional (governance) tensions, and tackled many political issues which this paper analyses because they are still insufficiently explored in the literature. The main contribution of the paper is the discussion of the reflexive learning between the two projects concerning the institutional tensions (reductive injunctions, black boxes, antagonisms, post-political) and moments of confluences (impacts on municipalities strategies and policies, rebalancing of distribution of power, removal of regulatory barriers, emergence of a multi-level and multi-technical approach) we encountered.