Abstract
The project focused on 2 farm anaerobic digesters, 1territory digester and 2 digester-composting plants of urban waste (1 treating biowaste and 1 treating the fermentable fraction of household waste). Five sampling campaigns were carried out on 1 year for each site with collection of raw digestate, separated digestates (solid and liquid phases), and where possible post-processed digestates (composts, dried digestate, membrane filtration condensate). In the absence of a regulatory framework for digestate, their physical and chemical characteristics were analyzed using existing standards for fertilizer and amendment (NFU44-051, NFU44-095 and NFU42-001) and by rheological tests, dehydratability, and biological activity (respirometry, methanogen potential). The behavior of raw and separated digestate (liquid and solid phases) of the five sectors was studied in laboratory pilots during various post-processing: drying or composting for raw digestates and solid phases, biological oxidation or membrane separation for liquid phases. Whenever possible, the performance in terms of sanitization, drying, gaseous emissions and energy consumption during processing was determined. The composition of the products obtained was analyzed. The agronomic value of raw, separated and post-processed digestates, and the benefits/ risks associated with their return to the soil, were determined by tests in the laboratory and in the field, and modeling. These tests were used to determine the nitrogen fertilizer value and risk of volatilization of ammonia and N2O emission in the short term after spreading. The contribution to soil in the medium term, carbon (C) and nitrogen (N) mineralization dynamics and the ability of the contributions of digestates to maintain organic matter stocks in soils, risk of phytotoxicity and simulation of C and N fate into the field were determined. The data obtained by the project partners combined with data from real sites and, when necessary, bibliographic data were used for the environmental assessment (using the Life Cycle Analysis) and the economic evaluation of digestate post-treatment in comparison to a direct application of raw digestate.