Spectral Analysis of Dissolved Organic Matter from Biochar

Rice husk and sawdust are the focus of agricultural and forestry waste treatment and utilization. It has become a hot topic of research to make rice husk and sawdust into biochar and use it in environmental pollution and prevention, but there are little studies of dissolved organic matters in rice husk and sawdust biochar. Rice husk and sawdust biochars were prepared under different temperatures from 200 to 700 degrees C. The characteristics of DOM from the biochars were analyzed by UV-Vis spectroscopy, three-dimensional fluorescence spectroscopy and infrared spectroscopy, in order to find the influence of different pyrolysis temperature on biochar DOM. The results showed that DOC concentration in rice husk and sawdust biochar decreased with the increase of pyrolysis temperature, and the DOC concentration in sawdust biochar was much higher than that in rice husk biochar at the same temperature. The UV-Vis spectrum curve of the biochar DOM of rice husk and sawdust gradually decreased with the increase of wavelength, and the absorbance of biochar DOM of rice husk first increased and then decreased with the increase of pyrolysis temperature, while the biochar DOM of sawdust continued to decrease. At the same time, the ultraviolet characteristic parameters (SUVA(254) and SUVA(260)) of DOM from rice husk and sawdust biochar had the same changing trend with the increase of pyrolysis temperature, and the parameters of rice husk biochar DOM were higher than those of sawdust DOM at the same temperature. Three dimensional fluorescence spectra showed that the fluorescence peaks of rice husk and sawdust biochar DOM were mainly in the bands of lambda(ex/em) =300 similar to 315/400 similar to 425 and lambda(ex/em) =210 similar to 245/380 similar to 435, respectively representing humic and fulvic acid fluorescence peaks, which could be used to represent humic degree and hydrophobic component content of biochar DOM. With the increase of temperature, the humation degree and hydrophobic component content of the biochar DOM of rice husk first increased and then decreased, while the biochar DOM of sawdust gradually decreased. Moreover, the autochthonous index (BIX) of those DOM was not strong, indicating that the bioavailability and protein-like ratio of those DOM were low. The humification index (HIX) of DOM from rice husk biochar increased first and then decreased with the increase of temperature, while that of sawdust decreased gradually. In addition, the infrared spectrum results showed that, with the increase of pyrolysis temperature, the content of -OH in DOM of rice husk and sawdust biochar decreased gradually, the -CH2 and -CH2 did not change significantly, the aromatic ring C=C, C-H was enhanced, and the degree of aromatization was enhanced.