Water distribution in biowastes and digestates of dry anaerobic digestion technology

Moisture content and water distribution are important parameters to design and operate dry anaerobic digesters. In this study, two techniques were validated and used for determining the water distribution (hydration, vicinal, capillary and free water fractions): water sorption isotherms and thermo-gravimetic drying tests. Four biowastes and four associated digestates were sampled in two industrial plants treating Organic Fraction of Municipal Solid Waste and Green Wastes by dry digestion technology. Moisture sorption isotherms have shown that the hydration water fraction and vicinal water fraction of biowaste and digestates are similar, indicating that these fractions are not affected by the anaerobic digestion. Drying tests have demonstrated that the capillary structure changes with the microbial degradation, and that the capillary water fraction is more important in the digested media than in the original biowastes.

► Water distribution of biowastes and associated digestates was determined.
► Hydration and vicinal water fractions are not affected by the anaerobic digestion.
► Capillary structure changes with the microbial degradation.