甲基叔丁基醚(MTBE)蒸腾流浓度因子(TSCF)的试验评估

甲基叔丁基醚(MTBE)是北美燃料市场最常用的汽油添加剂，由于在土壤中的不吸附性和极高的水溶性．MT-BE已成为一种蔓延性的地下水污染物．植物修复技术被认为是目前对MTBE污染治理最为有效的方法之一．蒸腾流浓度因子（TSCF)作为植物修复技术中十分重要的参数，其通常是用污染物的辛醇-水分配系数(Kow)直接评估的。由于不同植物其体内脂肪含量不同，所以如果仅用污染物的Kow值来计算其TSCF值，往往不能准确表达污染物在植物体内的传输行为．由于MTBE在植物体内不发生降解，植物挥发是MTBE植物修复技术中唯一的作用机理．本实验用一自行设计的植物反应器来测定MTBE在不同温度条件下的TSCF值．长出新根须和嫩叶的柳树(Salix alba)枝条在一容积500mL的植物反应器中生长9-12d(其中MTBE溶液500mL，浓度4．81-6．60mg／L)来观察柳树对MTBE的吸收。MTBE的去除率和柳树的蒸腾量之间的关系用来计算其TSCF值．在15℃，20℃和25℃条件下，MTBE的TSCF值分别为0.58,0.75和0.49．本实验结果表明，柳树对MTBE的吸收是一个被动的行为，并且MTBE在柳树体内随蒸腾流的传输也有一定的限度。图2表1参11。

ESTIMATION OF TRANSPIRATION STREAM CONCENTRATION FACTOR (TSCF), A PHYTOREMEDIATION PARAMETER, FOR METHYL tert-BUTYL ETHER (MTBE)

This paper presents a numeric estimation of MTBE transpiration stream concentration factor (TSCF), an important parameter for the design of engineered MTBE phytoremediation systems, using the experimental data from plant uptake tests in a carefully designed bioreactor at 15～25 ℃. Pre-rooted willow (Salix alba) were kept in an Erlenmeyer flask of 500 mL with approximately 500 mL spiked aqueous solution for 9～12 d. MTBE concentrations were 4.81～6.60 mg/L. Samples were taken directly from the solution with a needle and injected to a purge and trap unit. Results from willow uptake tests indicated that the fraction of MTBE removed from the test systems strongly correlated with volume of water transpired in a temperature range of 15～25 ℃. The relationship between percent of mass reduction in aqueous solution and volume of water transpired was used to determine the observed TSCF value for MTBE. Due to the volatilization of MTBE involved in this test, the corrected TSCF values for MTBE were computed to be 0.58, 0.75 and 0.49 at 15 ℃, 20 ℃, and 25 ℃, respectively. These results indicated that the uptake of MTBE by willow was in a restricted passive manner and MTBE was unable to significantly transport through the transpiration stream of rooted vascular plants. Fig 2, Tab 1, Ref 11