Turning Leucaena leucocephala bark to biochar for soil application via statistical modelling and optimization technique

Soil applicable biochar has been prepared from bark of Leucaena leucocephala wood which is a waste generated during its pulping and papermaking process. The slow pyrolysis process adopted for this purpose has been modelled and optimized employing central composite design and desirability function under response surface methodology taking temperature (308-592 °C) and time (35-205 min) as independent variable while yield, loss on ignition, stable organic matter, oxidisable carbon and carbon liability index as dependent variable. L. leucocephala bark was characterized in terms of proximate analysis (moisture 4.90%, ash 7.20%, fixed carbon 18.10%, volatile matter 69.80%), elemental analysis (carbon 45.78%, hydrogen 10.67%, nitrogen 1.77%, oxygen 32.08%, sulphur 0.09%), lignocellulosic composition (holocellulose 45.86%, hemicellulose 15.01%, lignin 34.75%) and compared with a wide range of feedstocks to find its suitability towards biochar production. The optimum pyrolysis temperature and residence time were found to be 350 °C and 60 min respectively which gave biochar yield 53.16%, loss on ignition 88.17%, oxidisable carbon 28.82%, stable organic matter 38.48%, and carbon liability index 0.32. The biochar produced at optimum conditions were characterized by proximate analysis (moisture 0.65%, ash 11.83%, fixed carbon 40.2%, volatile matter 47.57%) and elemental analysis (carbon 62.91%, hydrogen 3.12%, nitrogen 2.65%, oxygen 20.74%, sulphur 0.05%). The O/C ratio of 0.25 and H/C ratio of 0.60 confirmed its life between 100-1000 years and appropriateness for soil application as well as carbon sequestration.