Characterization of the Residue (Endocarp) of Acrocomia aculeata and Its Biochars as a Potential Source for Soilless Growing Media

Abstract

Endocarp residues remaining after coconut oil extraction from Acrocomia aculeate are traditionally used for combustion as fuel. As an alternative, we propose its conversion into biochar to substitute peat in planting substrates. To test the feasibility of this approach, untreated endocarp residues (particle size approx. 10 mm) and materials shredded into particles of 4 and 1 mm were pyrolyzed at 200 °C, 325 °C and 450 °C and were subsequently characterized. The pyrolysis-induced loss of organic matter increased the ash contents and pH. Nuclear magnetic resonance (NMR) spectroscopy confirmed the aromatization and a loss of carboxyl C with an increasing pyrolysis temperature. This is commonly associated with an enhanced biochemical recalcitrance. The particle size of the feedstock had no significant effect on the chemical composition or microporosity (BET-adsorption with COs) of the biochars, but affected their water holding capacity. With respect to macro- and micronutrients, only the potassium and Olsen P levels occurred in concentrations that are optimal for tomato seed growth. The low nitrogen level of the products may be advantageous for hydroponic culturing since it allows for a higher flexibility for the adaptation of nutrient contents based on the needs of the used culture.