Characterization of Food Waste and Its Digestate as Feedstock for Thermochemical Processing

The products of a commercial one-stage anaerobic digestion and a laboratory-scale pyrolysis of raw food waste (RFW) and digestated food waste (DFW) were characterized to evaluate the treatment effect, product yield, and physicochemical properties. The pyrolysis of the RFW and DFW resulted in generation of 7.4 and 5.3 wt % of gas and 60.3 and 52.2 wt % of bio-oil, while biochar yields decreased with an increase in the pyrolysis temperature. Differential thermogravimetric tests of RFW and DFW show 20% in both solid residues produced at a temperature of 550 °C, indicating a relatively low impact of the digestion process on the RFW. The mineral matter content was found to be lower for RFW compared to DFW. The variation in the content of fixed carbon and volatile matter reflected the effect of anaerobic degradation of the food waste. The bio-oils showed a low concentration of phenols, esters, and derivatives of hydrocarbons for DFW compared to RFW. The specific heat capacities were determined for RFW and DFW, while their morphological properties at different temperatures were equally considered using scanning electron microscopy and Fourier transform infrared spectroscopy. The results of this study provide indicators for treatment process assessment and measures to increase value-added products from food waste.