Effects Of Biochars On Adsorption And Desorption Of Three Fluoroqu- Inolones Antibiotics On Tropical Soils

Biochar is a carbon-rich solid material produced by pyrolyzing biomass in the partial or total absence of oxygen. In addition, a number of investigations have also revealed biochar's potential to be a low-cost adsorbent to control pollutant migration in soils. Biochars have an important influence on the environmental behavior of pollutants in soil. In this paper, a series of biochars was prepared by pyrolyzing bagasses, a typical tropical agricultural wastes, at three different pyrolysis temperatures (350?,450?,550?), which was referred as BC350, BC450, BC550. The compositions of biochars were characterized by elemental composition (CHN), fourier transform infrared spectroscopy (FTIR), BET specific surface area analysis, and so on. This paper studied adsorption and desorption of three fluoroquinolones antibiotics on typical tropical soils, and revealed the dominant mechanism of three fluoroquinolones antibiotics adsorption, and studied the effects of biochar on adsorption and desorption of three fluoroquinolones antibiotics on Latosols, and revealed the dominant mechanism of three fluoroquinolones antibiotics environmental behavior on biochar soils. The detailed results were as followed:1. Three biochars were generated from bagasses at different pyrolysis temperatures, yields, ash contents, pH and surface structural characteristics of biochars were discussed.(1) During the process of preparation, the pyrolysis temperatures could significantly affect yields, ash contents, pH of biochars. With the increase of pyrolysis temperatures, the carbonization degree, ash contents and pH increased gradually, the yields decreased gradually. The order of pH was as followed:BC550>BC450>BC350, which BC550 presented alkaline (pH=7.96).(2) According to the total elemental analysis, the highest content of element in biochars was carbon. With the increase of pyrolysis temperatures, the C, H and other element in bagasses were progressively pyrolyzed, C/H ratio increased, and the aromaticity increased gradually.(3) Different surface structures of three biochars were generated at different pyrolysis temperatures. If biochars were generated at low pyrolysis temperatures, the surface was relatively smooth. With the increase of pyrolysis temperatures, the organic fraction in bagasses was progressively pyrolyzed and the surface roughness of biochars increased. The pores of biochars were suddenly developed. According to the investigation of specific surface and pore structure, three biochars contained many micropores. With the increase of pyrolysis temperatures, the micropores and specific surface increased. The order of specific surface and total pore volume was as followed:BC550>BC450>BC350.(4) According to FTIR analysis, biochars contain of carboxyl, hydroxyl and other oxygen-containing functional groups, different number of functional groups in three biochars. According to boehm titration method analysis, the order of oxygen-containing functional groups was as followed:BC350>BC450>BC550. If biochars were generated at low pyrolysis temperatures, the amount of oxygen-containing functional groups was relatively higher. With the increase of pyrolysis temperatures, the amount of acidic groups decreased gradually, the amount of alkalinity groups increases. But the amount of decrease in acidic group was greater than the amount of increase in alkaline groups, the total amount of functional groups decreased gradually.(5) With the increase of pyrolysis temperatures, the CEC of biochars increased, the order of CEC was as followed:BC550 (108.53coml/kg)>BC450 (52.69coml/kg)>BC350 (42.87 coml/kg).2. This paper focused on adsorption and desorption of three fluoroquinolones antibiotics on typical tropical soils.(1) The experimental data of three fluoroquinolones antibiotics on Latosols were best described by the Freundlich and Langmuir model. Soils had a strong adsoption capacity on three fluoroquinolones antibiotics. Different sorption behaviors of same antibiotics were observed on tropical soils, with the lgKf values of norfloxacin varying greatly from 2.522 (Torrid red soils) and 2.986 (Latosols) to 3.137 (Paddy soils); the lgKf values of ciprofloxacin varying greatly from 2.356 (Torrid red soils) and 2.850 (Latosols) to 3.073 (Paddy soils); the lgKf values of ofloxacin varying greatly from 2.854 (Torrid red soils) and 3.086 (Latosols) to 3.106 (Paddy soils).(2) Adsorption isotherms of three fluoroquinolones antibiotics on tropical soils resembled the L-type curves. The adsorption capacity values, adsorption strength values and the maximum adsorption values of three fluoroquinolones antibiotics on paddy soils were higher than that Latosols and Torrid red soils, This may be related to higher content of organic matter and clay in Paddy soil.(3) Desorption rates of three fluoroquinolones antibiotics were higher than adsorption rate on three tropical soils, and the apparent sorption-desorption hysteresis was found. According to average hysteresis index, hysteresis was most apparent for norfloxcin than that for ciprofloxacin and ofloxacin, with the average hysteresis index of norfloxacin varying greatly from 0.366 (Torrid red soils) and 1.121 (Latosols) to 2.253 (Paddy soils); but the average hysteresis index of ciprofloxacin varying greatly from 0.099 (Torrid red soils) and 0.136 (Latosols) to 0.125 (Paddy soils). Strong retention, sorption-desorption hysteresis of three fluoroquinolones antibiotics on tropical soils, indicated existence of potential environmental risks.(4) The dominant mechanism of three fluoroquinolones antibiotics adsorption was physical adsorption on tropical soils; Mechanism of adsorption of three fluoroquinolones antibiotics on tropical soils included surface adsorption and partition. When equilibrium solution concentration was low, the surface adsorption was predominant. With the increase of equilibrium solution concentration, surface adsorption was saturated, afterwards, the partition was predominant.3. Effects of biochars on sorption and desorption behavior of three fluoroquinolones antibiotics on tropical soil(Latosols) was discussed.(1) Adsorption on biochar-amended (1%) soils included two steps of fast and slow reaction; Adsorption/desorption of antibiotics reached adsorption/desorption equilibrium after 24h. Equilibrium solution concentration of antibiotics was essentially the same and the adsorption/desorption rate decreased.(2) Three biochars had strong adsorption capacity on norfloxacin. The sorption data over the entire range of norfloxacin concentrations were better described by the Freundlich model (r=0.936) rather than Langmuir model (r=0.899). There was significant difference among adsorption of norfloxacin on three biochars, the order of lgKf values was as followed:BC550 (4.515)>BC450 (11.465)>BC350 (13.742). With the increase of pyrolysis temperatures, the adsorption capacity of norfloxacin on biochars increased gradually.(3) Biochar amendment rates were set at 0.1%,0.2%,0.5%,0.8% and 1.0%(w/w). Biochar could significantly increase the sorption of Latosols. The sorption quantity would increase with the increasing quantity of biochar; the Kd value of biochar-amended soils was 1.04-6.88 times higher than soils without biochar. The desorption data over the entire range of antibiotics concentrations were well described by the Freundlich equation and Langmuir equation with r>0.949; Adsorption isotherms of three fluoroquinolones antibiotics on Latosols was changed after amending with biochars.(4) Desorption process of three fluoroquinolones antibiotics on biochar-amended soils were not reversible process of adsorption. The single-step desorption isotherms suggested that sorption/desorption of antibiotics in the soils were consistently hysteretic. The hysteresis index values of norfloxacin on biochar-amended soils was 1.24?2.62 times higher than soils without biochar; The hysteresis index values of ciprofloxacin on biochar-amended soils were 1.25?1.83 times higher than soils without biochar. But the hysteresis index values of ofloxacin on biochar-amended soils was lower than soils without biochar (H=1.366).(5) Mechanism of adsorption of three fluoroquinolones antibiotics on biochar-amended soils included surface adsorption and partition. Microporous absorption was the direct cause which led to sorption-desorption retardation. Antibiotics could be absorbed by more micropores in biochar-amended soils, which led to the enhancement of desorption retardation. Therefore, application of biochars to soil may be expected to change many transport processes and decrease the ecology risk.