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

Abstract

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.

Life Cycle Analysis of Energy Production from Food Waste through Anaerobic Digestion, Pyrolysis and Integrated Energy System

“…In this study, 1 kg of food waste was established as the functional unit. Details and characteristics of the food waste used in the modelling were described previously [13,28].…”

“…The mesophilic AD system generates methane, which is converted to electricity (supplied to the Australian national grid for distribution) and heat through the combined heat and power (CHP) system. Some of the operational data of the AD process may be obtained in the previous studies [13,28], as summarized in Table 1. Part of the generated heat is used for de-watering of the digestate, control of the AD process, and feedstock sterilization when necessary.…”

“…Details of the energy distribution yield and characterization results of these products produced at industrial pyrolysis temperature (500 • C) were presented previously [13,28]. Heating rate may be defined to influence the choice of products during pyrolysis.…”

“…These data were obtained by combination of different sources; mainly from a functional industrial one-stage anaerobic digestion food waste treatment plant in Sydney, laboratory tests, methods, and analysis of samples, as reported previously [13,28], and standardized by the Eco-invent 3.1 database [32]. Material and energy consumption associated with the waste treatment processes involved in the pyrolysis and the proposed integrated management scenarios were obtained from the laboratory experiments [13,28]. Since the industrial scale pyrolysis provides the inert condition simulated by N 2 in the laboratory scale, nitrogen was therefore excluded in the evaluation while maintaining other data obtained through the pyrolysis trials.…”

“…In case B (pyrolysis), besides the grid energy saved, fossil fuel consumption was treated as potential saving, since bio-oil was considered as a substitute for light fuel oil in boilers and biochar was characterized as substitute for coal in industrial furnaces for heat production. This assumption was predicated on the physicochemical properties of the pyrolyzed raw food waste, as detailed in previous studies [28].…”