Biochar is a charcoal resulting from the combustion of biomass under conditions of little or no oxygen. Agricultural and forestry waste are the ideal feedstock as they produce biochar suitable for soil amendement (Verheijen et al., 2010). As a result of the pyrolysis different byproducts are created: biochar, liquid fuel, and gas (Demirbas et al., 2002). Among the byproducts biochar is the most attractive due to its economic and environmental benefits, on one hand when applied to the soil, the biochar improves its physical and chemical characteristics and on the other hand acts as a carbon sink which helps mitigating climate change (Chan et al., 2008). In contrast to formerly used methods pyrolysis can be controled to increase the amount of biochar produced, reducing negative impacts and minimizing the use of external sources of energy (Qian et al., 2015). The three most efficient technologies used to pyrolize biomass are: kiln pyrolysis, microwave assisted pyrolysis,and hydrothermal carbonization (Meyer et al., 2011). These three methods are compared in terms of their byproducts yield; the amount of external energy they require; their possible negative effects; and the costs of the machines employed in their production.
ARCINIEGAS et al. (2019) studied this question.