Low-cost field production of biochars and their properties

Abstract

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 m 2 /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.

Evaluating the effect of biochar on salt leaching and nutrient retention of Yellow River Delta soil

“…When the branches burned to dark red char, they were knocked down to the ground, collected it and then sprayed with water-mist to extinguish immediately to form biochar. During carbonization, the temperature will rise rapidly and the water spray will immediately terminate the carbonization (Xiao, Feng, Yuan, & Wei, 2019). The basic properties of biochar are shown in Table 2.…”

Coupled effects of biochar use and farming practice on physical properties of a salt-affected soil with wheat–maize rotation

“…Biowaste of the local Salix fragilis L. was used to produce biochar in the field through an aerobic carbonization process via a coupled fire-water method (Xiao et al 2019a(Xiao et al , 2019b. The carbonization process had the dual features of the combustion on the surface of biomass and the oxygen-limiting pyrolysis inside of the biomass.…”

“…Briefly, Salix fragilis L. branches were ignited at one direction of a brick-constructed trough for aerobic carbonization at an average temperature of 502°C, followed by a water mist spray to dark red char at 0 min exposure time for the termination of the carbonization and the formation of biochar. Operating parameters that control the properties of biochar in conventional pyrolysis (Al-Wabel et al 2018), namely the heating rate, pyrolysis temperature, and residence time, were simplified to a single one in aerobic carbonization: exposure time, i.e., the time between a burning char fell to the ground and water spray was applied to terminate the pyrolysis (Xiao et al 2019b). The properties of biochar were determined by established methods, as described in Section 2.3.…”

“…Cations and anions in the soil extracts (soil: water ratio of 1:5 w/v) were measured by ion chromatography (ICS3000, Dionex) (Chaganti et al 2015). Biochar was analyzed for its ash content by heating in a muffle furnace at 800°C for 4 h, and for elemental compositions using an elemental analyzer (Vario Micro cube, Elementar, Germany) (Xiao et al 2019b). The concentration of acidic functional groups in biochar was determined by the titration method (the International Humic Substances Society 2019).…”

“…The concentration of acidic functional groups in biochar was determined by the titration method (the International Humic Substances Society 2019). The biochar was observed for its morphological features by a scanning electron microscope (Hitachi S-4800, Japan) and determined for its specific surface area by sorption of N 2 at 77 K, using a Quantachrome Autosorb-iQ analyzer, and applying the Brunauer-Emmett-Teller (BET) equation (Herath et al 2013;Xiao et al 2019b).…”