Effect of pH, Volatile Content, and Pyrolysis Conditions on Surface Area and O/C and H/C Ratios of Biochar: Towards Understanding Performance of Biochar Using Simplified Approach

Abstract

The objective of this study was to predict biochar properties [surface area and oxygen-to-carbon (O/C) and hydrogen-to-carbon (H/C) ratios] from pyrolysis conditions, volatile matter content, and pH using the k-nearest neighbor (KNN) algorithm. Such predictions were made for different types of biochar, derived from various sources, namely rice husks, rice straw, applewood chips, and oakwood. The relative significance of each parameter affecting the Brunauer–Emmett–Teller (BET) surface area, O/C ratio, and H/C ratio was reported. The BET surface area increased with an increase in temperature or pH but decreased with an increase in the volatile matter content. A relationship was identified between H/C ratio, biochar yield, volatile matter content, pH, temperature, and adsorption. According to the results obtained, volatile matter content was found to be the most significant parameter affecting H/C ratio, followed by temperature, adsorption, pH, and biochar yield but in the case of O/C ratio and surface area, adsorption was found to have the highest significance of all the parameters. Overall, this study is useful to estimate the performance of biochar (surface area, stability, and bonding ability). This will further help certain users (farmers, engineers, and soil and water remediation scientists) to refine the list of biochars suitable for their purpose without going through laborious and cost-intensive process of determining surface area and O/C and H/C ratios.