In a five years retrospective, it was not known how different combinations of these enhancement techniques could enhance further the waste degradation process or how the mechanical and hydraulic properties of waste changed or could change in time due to the implementation of these enhancement techniques. Little information existed about the inherent microbial dynamics or the geochemical processes occurring within the (bioreactor) landfill mass. In these last five years, the political perception has started to change slowly, thus granting, beside limited funds, “escape” windows that allow landfill operators to conduct R&D efforts to demonstrate the value and importance of bioreactor landfills within the wide range of waste management options. 2. The present: what we know now

Municipal solid waste degraded in (bioreactor) landfills undergoes a series of diverse and complex processes. Every year researchers around the world increase the knowledge not only on these diverse and complex processes, but also about other issues within the municipal solid waste management system (i.e. prevention, collection, reuse, recycling, alternative treatments, etc.).