Renewable Energies and Biochar: A Green Alternative for Reducing Carbon Footprints Using Tree Species from the Southern Andean Region of Ecuador

The urgent need for sustainable strategies to mitigate climate change has spurred the development of efficient carbon sequestration methods with minimal greenhouse gas emissions, presenting promising opportunities to produce biochar and, with this bioproduct, enhance crop productivity. Therefore, this research aimed to evaluate the carbon footprint produced by the low-temperature slow pyrolysis of biomass obtained from the pruning residues of four tree species present in parks and gardens of the southern Andean region of Ecuador. An electric reactor (ER), powered by 44 solar panels of 535 W each, was used to perform the pyrolysis process at 350 °C over four hours. For each species—Persea americana, Polylepis spp., Acacia spp., and Prunus salicifolia—three replicates of the process were conducted using 1.5 kg of biomass per trial. The results showed that Acacia spp. residues produced biochar with higher bulk density (0.303 g/cm3), organic matter (82.85%), total organic carbon (71.21%), oxygen (27.84%), C/N ratio (120.69), and potassium (459.12 ppm). The biochar produced from Prunus salicifolia exhibited the highest levels of pollutant gas emissions and carbon footprint (5.93 × 10−6 ton∙m−3 CO2 eq and 0.001067 ton∙m−3 CO2 eq, respectively). In contrast, the biochar produced from Polylepis spp. was the least polluting (0.001018 ton∙m−3 CO2 eq), highlighting its potential as a source for biochar production from tree species found in the southern Andean region of Ecuador. Meanwhile, the pyrolysis of Persea americana (avocado) resulted in very low gas emissions, although it exhibited the second-highest carbon footprint due to the high energy consumption associated with the process. In conclusion, this study identified Persea americana and Polylepis spp. as the best options for biochar production through pyrolysis, positioning them as viable alternatives for developing sustainable strategies to mitigate climate change.