Effects of Sugarcane Bagasse-derived Biochar on Adsorption and Desorption of Ciprofloxacin in Tropical Soils
In this study, a series of biochars were prepared by pyrolyzing sugarcane bagasses, a typical tropical agricultural wastes, at three different pyrolysis temperatures(350, 450, 550 ℃), which was referred as BC350,BC450 and BC550. The effects of biochars on the adsorption and desorption of ciprofloxacin on Latosols and the dominant mechanism of ciprofloxacin environmental behavior in biochar soils were studied. Results showed that the adsorption on Latosols and biochar-amended soils(w/w, 1.0%) included two steps, the fast reaction and the slow reaction; The adsorption kinetics of ciprofloxacin on Latosols and biochar-amended soils(w/w, 1.0%) were accorded with the pseudo-second-order kinetics equation( r 0.989, p 0.01); Biochar amendment rates were set as 0.1%,0.2%, 0.5%, 0.8% and 1.0%(w/w)of soils. Biochars could significantly increase the adsorption of Latosols. The adsorption quantity would increase with the increasing quantity of biochar. The adsorption and desorption data over the entire range of antibiotics concentrations were well described by the Freundlich equation and Langmuir equation with r0.984 and p0.01. The desorption process of ciprofloxacin on biochar-amended soils were not a reversible process of adsorption. The single-step desorption isotherms suggested that the adsorption/desorption of ciprofloxacin in the soils were consistently hysteretic. The hysteresis index values of ciprofloxacin on biochar-amended soils were 1.32 ~1.86 times higher than Latosols. The mechanism of adsorption of ciprofloxacin on biochar-amended soils included surface adsorption and partition. Microporous absorption was the direct cause which led to sorption-desorption retardation. The biochar-amended soils had fixation effects on ciprofloxacin, and ciprofloxacin adsorbed by biochar-amended soils were difficult to be desorbed. Therefore, the application of biochars to soil could change the transport processes and decrease the ecology risk.