Treatment of Wet Organic Waste by Hydrothermal Carbonization

Wet organic waste, including animal manures, sewage and activated sludge, and the organic portion of municipal solid waste, represents both a burden that must be dealt with as well as a material source for fertilizer and compost. Depending on how these wastes are treated, their properties and behavior when applied to soils can vary significantly. The high water-fraction present in wet organic waste is commonly a disadvantage in various treatment techniques such as composting and pyrolysis, requiring drying or the addition of dry matter. Similarly, a low C:N of some of these sources (e.g. poultry manure and domestic sludge) may be challenging for commonly used biological treatments. Hydrothermal carbonization (HTC) is a technology that, as suggested by its name, involves the presence of large water fractions, thus it is ideally suitable for the treatment of wet organic waste. This chapter will introduce the HTC process, providing an overview of the main chemical conditions and reactions involved in the conversion of wet organic waste. Then, the various applications of the generated products will be discussed, with a particular focus on the addition to soils.