Effect of pyrolysis conditions on biochar characteristics and water evaporation

Biochar is produced by the thermal decomposition of carbon-rich materials in a limited oxygen atmosphere. A wide source of raw materials can be used, and depending on the source material and pyrolysis conditions, outstanding features can be obtained, such as high specific area, porosity, functional groups, and high-stable carbon. Thus, biochar properties make it suitable for various applications for pollutant sorption, energy storage, carbon sequestration, and soil improvement. The significance of biochar as a soil amendment is attributed to the improvement of both the physical and biochemical properties of soil, the increase of soil fertility and productivity, the rise in water retention, and the improvement of microbial activities. Water retention in soil is affected by adding biochar, which interacts with soil particles and could result in the formation of macroaggregates with higher specific surface and porosity. This results in the formation of more binding sites for water molecules and thus increases the water retention of soil. Except for the interactions of biochar-soil mixture, biochar-self properties could affect water holding capacity. Specific surface, particle size sphericity, and surface functionality have been shown to affect water-holding capacity. In this study, biochars were produced using coffee spent grains and crushed olive grains under different pyrolysis conditions (300 to 900^oC). Biochar was characterized for the specific surface, pore volume and size, and surface functional groups.