Low-cost field production of biochars and their properties
Biochar has been intensively investigated for carbon sequestration, soil fertility enhancement, and immobilization of heavy metals and organic pollutants. Large-scale use of biochar in agricultural production and environmental remediation, however, has been constrained by its high cost. Here, we demonstrated the production of low-cost biochar ($20/ton) in the field from Robinia pseudoacacia biowaste via a combined aerobic and oxygen-limited carbonization process and a fire-water-coupled method. It involved aerobic combustion at the outer side of biomass, oxygen-limited pyrolysis in the inner core of biomass, and the termination of the carbonization by water spray. The properties of biochar thus produced were greatly affected by exposure time (the gap between a burning char fell to the ground and being extinguished by water spray). Biochar formed by zero exposure time showed a larger specific surface area (155.77 m2/g), a higher carbon content (67.45%), a lower ash content (15.38%), and a higher content of carboxyl and phenolic-hydroxyl groups (1.74 and 0.86 mol/kg, respectively) than biochars formed with longer exposure times (5–30 min). Fourier-transform infrared spectroscopic (FTIR) spectra indicated that oxygen-containing functional groups of biochar played a role in Cd and oxytetracycline sorption though a quantitative relationship could not be established as the relative contribution of carbon and ash moieties of biochar to the sorption was unknown. Outcomes from this research provide an option for inexpensive production of biochar to support its use as a soil amendment in developing countries.
KeywordsBiowaste Exposure times Functional groups Cadmium Oxytetracycline
This work was supported by grants from the Chinese National Key Research and Development Program (2016YFD0200303), Key Research and Development Program of Shandong Province (2016CYJS05A01), and the National Natural Science Foundation of China (41501522). Mr. Guanhua Shen of Zhaoqing University is appreciated for analyzing the specific surface area of biochar. We are grateful to Anne Austin, Manaaki Whenua—Landcare Research, New Zealand, for editing the original manuscript, and to three anonymous reviewers for their constructive comments and suggestions.
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