Influence of biochar amendments to soil on the mobility of atrazine using sorption-desorption and soil thin-layer chromatography

Abstract

Biochars, the carbonaceous residue from biomass pyrolysis, have been proposed as an agriculture soil amendment to improve soil fertility and retain a broad range of environmental contaminants. The objective of this research was therefore to investigate whether the additions of cassava wastes-based biochars obtained at 750°C (noted as MS750) with the specific area of 430m2/g to an agriculture soil could effectively attenuate the transport of atrazine by using laboratory batch sorption studies and soil thin-layer chromatography. To illustrate the worst-case sorption, MS750 with different application percentages (w/w: 0%, 0.1%, 0.5%, 1%, 3%, 5%) were added into krasnozem soil only with 0.75% organic matter to determine sorption-desorption behavior and migration of atrazine. The results obtained indicated that the occurrence of cassava wastes-derived biochar significantly enhanced the sorption capacity of the soil for atrazine. The sorption affinity augmented as expected with application rates of MS750, and the distribution coefficients in biochar-added soils were greater than that in soil alone, likely due to enhancement of soil organic carbon content and favorable sorption domains for organic compounds caused by amendment of biochars. Sorption isotherms were characterized by nonlinear curves, which indicated the heterogeneous sites on MS750-soil mixture. Desorption work exhibited a remarkable impact of biochars amendment into soils on desorption of atrazine, in which an apparent hysteresis was undergone. This study clearly revealed that biochars from cassava wastes application enhanced retention of soil for atrazine to some extent, nevertheless, the magnitude of enhancement of the sorption affinity was still of dependence on the solution pH value, environmental temperature, as well as contact time between soil and biochars. The △Go values with less than −20kJ/mol and the effect of solution pH variation on sorption capacity of 6 sorbents indicated that the equilibrium process may be involved physisorption, as well as accompanied with chemisorption. The results from thermodynamic analysis showed that sorption of atrazine in soils amended with MS750 was thermodynamically endothermic. Positive correlation between the mobility level of pesticide and the addition percentage of biochars suggested that the application of biochars derived from cassava waste was available to retain pesticides and attenuate the leach into groundwater. These observations provide important information on the application of biochars produced at 750°C as engineered sorbents for soil remediation and compounds elimination.