Production of Acidic Bio-Char from Food Waste

Abstract

Bio-char is a carbon-rich solid, produced by pyrolysis of biomass at a high temperature in absence of oxygen. The process also produces a hydrocarbon gas, which upon condensation, produces a liquid fraction and a permanent gas. When applied in sandy soil, the bio-char increases the water retention, enhances nitrification, and alters acidity, hence, enhancing the life and growth of plants. In this project, the aim is to use food waste, a feedstock available in UAE, for the production of acidic bio-char in an auger reactor. To assess the effect of the pyrolysis temperature on the quality of the products, the process was carried out at six different temperatures within the range of 350−580 °C. The highest bio-char yield (50.2 %) was obtained at 350 °C while the highest bio-oil yield (48.9 %) was obtained at 550 °C. The food waste was found to produce acidic bio-char with pH=6.73 at the pyrolysis temperature of 440 °C, which is lower than the pH for most bio-chars produced from conventional woody biomasses. The bio-char surface area, water retention capacity and electrical conductivity were found to increase with increased temperature. In terms of stability, the bio-char was found to be relatively stable as per their position in the Van Krevelen diagram. The quality of the bio-oil produced from the food waste was found to be exceptionally high with very low water content and high heating value. In conclusion, this study, provided valuable information for the potential of food waste as a source of bio-char and bio-oil, hence contributing to the diversity of sources for soil amendment material and clean energy in the UAE. For future work, it is recommended to explore wider operating conditions to enhance the bio-char acidity, among these is to consider pre-treatment of the biomass, use of CO2 as a sweeping gas and increasing the bio-char residence time.