Impact Of Black Carbon On The Sorption/desorption Behavior Of Acetochlor On Soil/sediment

Black carbon (BC) which is produced from incomplete combustion of vegetation and fossil fuel is ubiquitous in terrestrial and aquatic environments, it have been reported to be as high as up to 45% of the total organic matter in soils and sediments. In addition to its important role in the global carbon cycle, BC in soil or sediment may also potentially contribute to the sorption and desorption of organic contaminants, and thus effectively influence the environmental process of those contaminants in soils and sediments. In this thesis, we firstly investigated the role of black carbon in the acetochlor sorption to soils and sediments, then the sorption and desorption isotherms for acetochlor under various BC contents in sediment were studied. The objective of this study was to assess the effect of the presence of small amounts of BC in soil or sediment on the sorption and desorption of acetochlor. The main results are as following.1. Sorption behavior of acetochlor on real soil or sediment. The sorption behavior of acetochlor on three natural soils and three natural sediments were tested. The results showed that sorption on soils/sediments included the partition and slow hole-filling processes. The sorption of acetochlor on soils/sediments followed the first order reaction. The sorption capacity of the sediments and soils increased with the increasing the relative BC content to total organic carbon. The higher the BC content the stronger the sorption capacity of acetochlor to sediments or soils. Hence, an f_BC-effect sorption model for acetochlor is established to predict its sorption capability.2. Impact of BC on the sorption/desorption behavior of acetochlor. We tested the sorption and desorption behaviors of acetochlor on sediment amended with different levels of the two BC (BC400 with SSA of 148.13 m²/g and micropores proportion of 46.2%; BC500 had SSA of 299.71 m²/g and micropores proportion of 88.9%), by means of batch equilibrium technique and successive single decant-refill cycle techniques, respectively. The results displayed that sorption capacity had obvious increases after addition of BC400 and BC500, respectively. Moreover, addition of BC500 resulted in a stronger sorption capacity. By the test of sorption-desorption of acetochlor on BC500-amended sediments, the results showed that the sorption capacities and apparent sorption-desorption hysteresis markedly increased with increasing content of BC in the sediment. And the contribution to nonlinearity of sorption and desorption isotherms for acetochlor under various BC contents in sediment was emphasized. When the content of BC in total organic carbon (TOC) was lower than 23%, the sorption isotherm had a significant linear correlation (p=0.05). In case of desorption, a significant nonlinear change could be observed when the content of BC was up to 13%. Increase of BC content in the sediment would result in shifting the sorption-desorption isotherms from linearity to nonlinearity, which indicated that contribution of BC to nonlinear adsorption fraction became gradually remarkable.