Insight to the physiochemical properties and DOM of biochar under different pyrolysis temperature and modification conditions

Two biomass feedstocks, Bamboo and Coconut, were used to prepare biochar at three significantly different pyrolysis temperatures (300, 600, 900 °C), and under HNO3 and NH3·H2O modifications. However, before applying biochar to practical applications, the content of DOM released into the environment and its stability need to be considered. Herein, the physiochemical properties and the variation of DOM released from biochar were investigated under different pyrolysis temperature and modification conditions. Results showed that as the pyrolysis temperature increased, the pH, specific surface area and carbon content increased, the yield and H/C decreased. Meanwhile, the DOC content of Coconut biochar (CC) and Bamboo biochar (BC) decreased by 64.6 % and 78.2 %, respectively. In addition, HNO3 destroyed the original surface structure, and significantly changed the abundance of -OH, CO, -COOH in biochar. At 900 °C, the specific surface area of HCC (CC modified by HNO3) and NBC (BC modified by NH3·H2O) reached the maximum of 76.5 m2·g−1and 101.49 m2·g−1, respectively. The maximum DOC content of 29.1 mg·g−1 was existed in HBC at 300 °C. The spectral analysis indicated that the DOM aromatization index (SUVA254) of NBC reached a maximum of 5.25 L·mg−1m−1 at 600 °C. Based on the Pearson correlation coefficient analysis, it was concluded that the pyrolysis temperature had greater correlation (P＜0.05) with the yield, DOC content and humification degree of biochar, and the modification conditions were significantly related to the aromatization and hydrophobicity degree of biochar.