Key words: recycling, compost, composting, green waste, organic waste recycling.
France produces annually nearly 600 million tonnes of waste including over 400 are organic waste. For the latter, composting is a process path in strong development, favored by the current regulatory and sociological context.
Another advantage, this process adapts to the volume to be treated. It makes it possible to process very large volumes or lower by implementing a more or less advanced technology. Whether municipal, agricultural or from the food industry, a dual regulatory and sociological context helps to promote composting treatment: the obligation to reduce 65% of waste landfilled, the growing reluctance of the agricultural land application of sewage sludge and the obligation for waste producers to reduce their nitrogen load or turning them into exportable products out of the "zone of structural surpluses'.
Which work for which objectives?
Faced with growing social demand for this waste treatment method, the goal of the research conducted at Cemagref is to optimize the composting processes from the point of view of their technical performance as their environmental impacts. The gaseous emissions, or gas odor compounds greenhouse such as methane, carbon dioxide or nitrous oxide, for example causing major environmental impacts.
Know the processes that govern the fate of nitrogen during composting is essential for reducing emissions. The research conducted at Cemagref on composting so have many objectives among which include global modeling treatment by composting, diagnosis and control of gaseous emissions, the development of new processes, the acquisition of experimental tools composting treatment simulation, methodological monitoring these treatments, tool for classifying the biodegradability of organic waste and stabilization level.
Assess the "compostable" waste
The "formulation" of the waste mixture to be treated (or its pre-treatment) and the process and the processing conditions are the main parameters involved in composting. These parameters bring into play different processes: biological processes related to the nature of waste, heat and mass transfer which depend on the process used and the processing conditions.
By studying biological processes, it is for example characterize the initial or residual biodegradability of waste before or during treatment, and thus lead to better management and optimization of composting processes. In this perspective, a respirometric tool is being developed within the team Sowaste Cemagref in Rennes. It allows the measurement of oxygen consumption associated with the biodegradation of an organic substrate. By modeling this consumption, we can quantify the various biodegradable organic fractions of the material studied. This method should assess the "compostable" of a substrate, value then used to optimize the formulation of mixtures or choose pre-treatment to apply. Using this tool at various stages of the composting process, it will be possible to evaluate the residual biodegradability of a material and thus to control or appraised process, but also to quantify the biological stabilization of composts end of treatment.