Hydrodynamic cavitation as an energy efficient process to increase biochar surface area and porosity: A case study

The effectivity of biochar as soil amendment depends on its physical and chemical characteristics, related to the type and features of the thermal production process, such as peak temperature, heating rate, holding time, as well as on the used feedstock. The textural characteristics of biochar in terms of surface area, pore size and pore volume distribution, important for its physicochemical properties, are critically dependent on the feedstock type, the production process, and possible further activation methods. This study was based on a single biochar type, resulting from slow pyrolysis at the working temperature of 550 °C of raw material from coppiced woodlands, as well as on a single experiment. For the first time, controlled hydrodynamic cavitation was proven as a fast and effective way to enhance the surface area of biochar by as much as 120%, while preserving or improving the respective chemical composition. The introduced technique, while easily applicable and scalable, showed far higher efficiency than the conventional method of increasing the working temperature of the pyrolysis process, with higher process yields by at least an order of magnitude. Moreover, hydrodynamic cavitation processes could be straightforwardly integrated with other consolidated methods, such as hydrothermal carbonization and chemical activation, possibly leading to effective synergism.