Involvement of Cooking Oils in Hydrothermal Carbonization of Food Waste

The fatty esters in cooking oil may not be inert organics. Their potential involvement in hydrothermal carbonization (HTC) of food waste was investigated in this study. Cooked cabbage (vegetable) and rice (staple food) were selected as the feedstock and their HTC in the presence of (vegetable oil) and lard (animal fat) was conducted at 260 °C for 10 h. The results indicated that presence of the cooking oil increased the hydrochar yield (i.e., 71.5% increase for HTC of rice with lard) originating from the reactions between the oil-derived fatty acids and the food-derived alcohols, amines, etc. This significantly increased both the carbon and hydrogen contents and simultaneously reduced the oxygen content of the hydrochar. The additional aliphatics from the cooking oil formed on hydrochar remarkably reduced the thermal stability of the hydrochar, but increased the volatility and led to improved combustion performance through lowering the activation energy for combustion.