Characterization of dissolved organic matter in biochar derived from various macroalgae (Phaeophyta, Rhodophyta, and Chlorophyta): Effects of pyrolysis temperature and extraction solution pH.

Characterization of biochar-derived dissolved organic matter (DOM) can provide deep insight into potential applications of biochar. Herein, biochar from six macroalgae (Phaeophyta-Sargassum fusiforme, Sargassum thunbergii, and Sargassum vachellianum; Rhodophyta-Grateloupia turuturu and Chondria crassicaulis; and Chlorophyta-Ulva pertusa) were subjected to pyrolysis at different temperatures (200 °C-500 °C). The effects of pyrolysis temperature and extraction solution pH on the characteristics of the macroalgal biochar-derived DOM (MBDOM) were investigated via fluorescence excitation-emission matrix spectroscopy with parallel factor (PARAFAC) analysis. Five humic-like substances and one protein-like substance were identified. The distributions of the six PARAFAC components depended on the macroalgae species, pyrolysis temperature, and extraction solution pH. The proportion of the protein-like substance (0 %-46.77 %) was less than that of the humic-like substances (100 %-53.23 %) in a given MBDOM regardless of the extraction solution pH values. Fluorescence spectral indicators show that DOM from macroalgal biochar is more autochthonous and humified than that from the corresponding biomass. Hierarchical cluster analysis and redundancy analysis results further show that the macroalgae species, pyrolysis temperature, and extraction solution pH jointly affect DOM characteristics with varying contribution levels.