Conversion of waste into biofuel via hydrothermal carbonization method

The aim of this thesis is to convert animal and agricultural wastes into biofuels with high-calorific value using the environmentally friendly and sustainable hydrothermal carbonization (HTC) method. In the scope of this study, dairy cattle manure (SG) and olive residue (P) were mixed in equal proportions by weight and subjected to HTC to produce high-energy biofuels. The characterization and combustion performance of the hydrochars were also investigated. An optimization study for hydrochar production was conducted using various operational parameters including temperature (180–260°C), reaction time (0–180 min), solid-to-liquid ratio (1:5, 1:10), and initial pH value (3, 6). The highest energy density value of hydrochar was achieved under conditions of 260°C, initial pH 3, solid-to-liquid ratio of 1:5, and 180 minutes of reaction time, with an energy density of 1.75. The highest energy yield (136%) was observed at 180°C, pH 3, solid-toliquid ratio of 1:5, and 180 minutes of reaction time. Decrease in H/C and O/C molar ratios of the hydrochars indicate improved fuel quality. Thermal degradation processes of the hydrochars produced at 180, 220, and 260°C under nitrogen and air atmospheres were analyzed using thermogravimetric analysis (TGA), and the combustion indices (S) demonstrated their suitability as solid fuels. BET analysis revealed that hydrochars produced at 180°C and 220°C had higher surface areas compared to that produced at 260°C. Functional groups and surface morphologies of the hydrochars were determined using FTIR and SEM-EDX analyses, while hydrochar ashes were examined via XRF and SEM-EDX. Compared to the raw biomass, reductions were observed in Na₂O, K₂O, and Cl contents, while concentrations of trace elements such as Cd, Cu, Fe, Ni, Pb, and Zn increased. Total Organic Carbon (TOC) and Total Nitrogen (TN) levels were measured in the process water of HTC. As a result of this study, it was concluded that renewable solid fuels equivalent to lignite and sub-bituminous coal can be produced from waste materials through the HTC method. Keywords: dairy cattle manure, olive residue, hydrothermal carbonization, hydrochar, renewable energy