Energy recovery as added value from food and agricultural solid wastes

Abstract Agricultural and food industries produce enormous quantities of wastes globally, that further affects public health and the environment by their disposal. Food and Agricultural Organization has reported that as many as 1.3 billion tons of food per year is lost along the food supply chain. Thermal treatments such as combustion, pyrolysis, hydrothermal carbonization (HTC), and hydrothermal liquefaction (HTL) and gasification are the most commonly used methods for the management of such waste. However, combustion, also known as incineration, is difficult due to environmental and social concerns. An alternative which is considered safe and is particularly applicable to dry waste is pyrolysis instead of combustion for clean air. HTC permits the use of wet biomass without the prior need for dewatering and results in the production of desirable carbon-rich materials which have specific properties and energy applications (hydrochar). In HTL, biomass is hydrolyzed and broken down into smaller, more unstable components, which are then repolymerized to produce light gases (e.g., CH4, CO2, CO, H2), char (solid residue), water-soluble substances, as well as a highly viscous hydrophobic bio-oil. In the hydrothermal (HT) gasification, gaseous products, predominantly CO2, CO, H2, CH4, and C1–C4 carbon gases are formed after the reaction of biomass waste with water in presence of elevated water temperatures and pressures. In comparison to hemicellulose and cellulose, a successful lignin HT gasification is more difficult to achieve, owing to repolymerization, formation of tar and char and high reactivity of low-molecular weight lignin. Another biochemical conversion process which is effective for lignocellulosic wastes is bioethanol production. Cellulosic ethanol production technology involves pretreatment, hydrolysis, and fermentation. Another promising technique is to generate methane from food processing and other wastes with high moisture contents and which are easily biodegradable, such as fruit and vegetables in the anaerobic digestion process. These wastes are primarily derived from the manufacturing, transporting, storing, distributing, and consuming of fruits and vegetables. It is essential for a sustainable agro-food sector to consider the circular bioeconomy model (“reduce, reuse and recycle”). From a circular bioeconomy point of view, agro-food waste should be considered as a resource and not as a waste. This consideration would give it high energy value and it could be considered as a source of value-added compounds. In this chapter the potential of agro-food waste as a source of energy is reviewed.