Can anaerobic co-digestion improve agronomic characteristics of digestate? Case of study of Treviso's WWTP

One-year monitoring data of a full-scale mesophilic anaerobic co-digestion process, treating waste activated sludge and the organic fraction of municipal solid waste, are analyzed in this paper, and with regard to the quality of digestate obtained. The process at steady state conditions shows a good stabilization of organic matter, reaching the 45% of volatile solid removal. As requested by the End-Of-Waste criteria, heavy metals, dioxins and furans, and pathogens content are analyzed. The chlorinated compounds show low concentrations (5.643 ngI-TE/kgdw of PCDD/F and 32.03 µg/kgdw of PCBs), while heavy metals (Cd, Cu, Pb and Zn) and E.coli (4×104 CFU/g) values are higher than the proposed limits. A strategy for improving the process performances and the quality of the final effluent is discussed, taking into account the OFMSW/WAS ratio variation in the inlet mixture and the thermophilic working temperature for pathogens removal.