Sustainable intervention of food waste treatment process and products
thesisposted on 2022-03-28, 14:33 authored by Suraj Adebayo Opatokun
Due to resource scarcity and impacts amelioration, efforts are ongoing to widen recycling capacity of organic waste and smartly appropriate its products to ensure optimization and a zero waste system. In this work, food waste is treated with full consideration of two treatment streams (anaerobic digestion and pyrolysis) using the energy, environment, agronomic and socio-economy as indicators to evaluate the sustainability extent of these treatment processes and their products. Review of the organic waste treatment processes and their products was explored to identify treatment gaps and its effects on the products vis-à-vis sustainability. Fresh food wastes were collected from Macquarie and Eastwood shopping centres and sampled compositely for both biochemical (anaerobic digestion) and thermochemical (pyrolysis) treatments. Characterization results of fresh food wastes were compared with food wastes in other part of the world through a review to reflect properties parity. Meanwhile, to reduce experimental cost and save biochemical digestion time, digestate was collected from EarthPower Technologies Sydney Pty Limited (a commercial food waste to green energy company). This was equally characterized analytically to evaluate its organic, inorganic and elemental constituents. The raw food wastes and the digestate were then pyrolysed separately at different temperatures (300,400, 500 and 700°C) to evaluate temperature effect on the products' (biogas, biooiland the biochar) quantity and properties. The energy proficiency of these treatment processes using food waste and its digestate were evaluated through a novel energy harvesting system (EHS) after discrete assessment of the two processes (anaerobic digestion and pyrolysis). The hybrid EHS wherein anaerobic digestion was sequenced with pyrolysis provided the highest transitional energy base products. This was accomplished using industrial pyrolysis temperature (500°C). The biochar produced through pyrolysis from the raw food waste were activated using CO2 (a major constituent of the biogas generated) to drastically reduce greenhouse gas (GHG) emission. This activated and oxidised chars were compared with commercial activated carbon. The produced activated chars(with surface area range of 797.2 to 1024.7m²/g) were evaluated as a component of pressure swing adsorption (PSI) for refinery off gases (ROG) treatment and or purification. Raw food waste oriented chars adsorbed 330 to 380mg/g of benzene gas and 4.1 to 4.4mmol/g of CO2. The abolition of CO2 flaring and scrubbing of C6H6 gas are significant environmental impact amelioration. Similarly, the digestate (DFW) and digestate derived chars (PyD500) potential for soil enhancement and or fertilizer were evaluated. Sand to substrate rate, germination index, water retention capacity and plant availabl ewater were used to assess agronomic capacity of these products (DFW andPyD500). DFW provided the best reaction to plant available water with increasing application rate in the sandy soil considered. However, PyD500 delineated better phytotoxicity, water holding capacity and nutrient sorption rates compared to DFW. Finally, life cycle analysis (LCA) of the three processes (commercial one stage anaerobic digestion, pyrolysis and the integration or sequence of AD and pyrolysis) and their products are considered to gauge the likely environmental impacts putting all in perspective. The sustainability stance of variables (input and outputs) and treatment processes are determining with energy,environment, agronomic and socio-economy as indicators for a life cycle analysis. This is expected to widen and broaden treatment of food wastes and ensure the fitness and robustness of the model developed in most part of the globe.