Wine making industry wastes biodegradable properties characterization for biogas conversion

Grape marc is a very common type of biomass across the world, available in large quantities, with high moisture content which makes it suitable for biological treatment rather than other thermal treatments for energy recovery. The aim of this paper is to reveal the biodegradable characteristics of grape marc using two of the most applied parameters to determine the biomass stability through respirometric methods: chemical oxygen demand (COD) and dynamic respiration index (RI). Different analyses were performed on the dried materials represented by white and red grape marc: proximate analysis, elemental analysis, high and low heating value determination. COD was determined for the two types of biomass with a standardized method using potassium dichromate. The evolution of the respirometric index in time (RI, RI24) was determined using a dynamic respiration reactor developed at the University of Trento. The results obtained provide important information on the degradation occurring through the aerobic process, correlated with necessary time for biomass stabilization. The maximum values obtained are 675 mgO2 kg-1VS h-1 after 5 days for white grape marc and 894 mgO2 kg-1VS h-1 after 3 days for red grape marc. These differences are explained by the different technologies of obtaining white and red wine. The combination of anaerobic digestion followed by digestate composting could reveal important advantages from an energy point of view, by obtaining biogas after the first process and by limiting the energy consumption of the aeration necessary for the second process because of slow biodegradable properties of resulting digestate