Spectral Characteristics of Dissolved Organic Matter Released From Biochar at Different Pyrolysis Temperatures
ZHAO Min1,2, CHEN Bing-fa1,2, FENG Mu-hua1, CHEN Kai-ning1, PAN Ji-zheng1*
1. State Key Laboratory of Lake Science and Environment, Nanjing Institute of Geography and Limnology, Chinese Academy of Sciences, Nanjing 210008, China
2. University of Chinese Academy of Sciences, Beijing 100049, China
Abstract：The dissolved organic matter (DOM) released from biochar has complex biogeochemical characteristics, affecting the migration and transformation of pollutants, carbon cycle and many other environmental processes. Compared with researches on the physicochemical and structural characteristics of biochar, researches on biochar DOM are few. The spectral characteristics of DOM released by biochar driven by pyrolysis temperature are rarely reported. We choose cypress and bamboo biochar, which are common and have a good application prospect, as research object. Spectral characteristics of DOM released from two kinds of biochar under different pyrolysis temperature (100~700 ℃) were identified by ultraviolet-visible spectra，and three-dimensional fluorescence spectra combined with parallel factor method (3DEEMs-PARAFACA). The results show that the pyrolysis temperature determines the DOM release potential and spectral characteristics of biochar. The amount of DOM decreases when the pyrolysis temperature increase and 400℃ is the critical temperature. When the pyrolysis temperature is lower than 400 ℃, the biochar DOM is obviously released; but the release amount of DOM is low and tends to be stable when the pyrolysis temperature is lower than 400 ℃. The amount of DOM released from cypress biochar is apparently higher than bamboo biochar. During the pyrolysis process at low temperature (<300 ℃), a large number of UV-visible chromophore exists in the DOM of biochar, which decomposes gradually with the increase of pyrolysis temperature. We isolated two humic-like fluorescent components (C1 and C2) and one protein-like fluorescence component (C3) from the fluorescent dissolved organic matter (FDOM) by 3DEEMs-PARAFAC. Three components show different responses to pyrolysis temperature, humic-like components appeared fluorescent intensity peak at 300 ℃, and then decrease when the temperature rises. Meanwhile, the fluorescent intensity of protein-like component decrease from beginning to end. FDOM under low pyrolysis temperature (＜200 ℃) is dominated by protein-like substance, but humic-like substance predominated when pyrolysis temperature increase. In addition, pyrolysis temperature also affects many biogeochemical characteristics of two kinds of biochar. With the increase of temperature, the relative molecular weight, aromaticity, hydrophobicity and humification degree firstly increase and then decrease, but the peak appears in different temperature. Due to the differences in raw materials, the relative molecular weight, aromaticity, hydrophobicity and humification degree of bamboo biochar was significantly higher than that of cypress. The conclusion of this study further provides beneficial references for the study on the environmental behavior of biochar DOM and the environmental management and assessment in the engineering application of biochar.
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