汽油污染含水层中芳香烃的自然去除与生物降解特征

Natural removal and biodegradation of monoaromatic hydrocarbons (BTEX) in groundwater contaminated by gasoline: A pilot scale physical model

石油烃污染地下水是一个普遍而严重的环境问题。用砂卵石、中粗砂、细砂、粉砂和粘土等在实验室内按照自然界沉积物层序制作了一个含水层物理模型,具有给水、排水、监测、抽提、淋滤与注入等功能。利用该模型开展石油烃污染地下水的特征研究结果表明,苯、甲苯、乙苯和二甲苯(benzene,toluene,ethylbenzene,xylene;BTEX)各溶解组分能够被自然去除,其中甲苯自然衰减的速率系数为0.0575～0.1504d-1,二甲苯为0.0683～0.1046d-1,乙苯大约为0.0478d-1,苯为0.0178～0.0406d-1。甲苯与二甲苯容易被去除,然而苯的去除则需要较长的时间。作为BTEX去除反应的电子受体,溶解氧、硝酸盐在需氧或厌氧条件下具有优先利用的机会,而硫酸盐则缺乏优先利用的机会。BTEX溶解组分浓度的降低,加上电子受体浓度的降低,可以表明含水层存在需氧条件与硝酸盐还原条件下的内在生物降解作用。其意义在于通过增加含水层中电子受体的浓度,将有助于内在生物降解能力的增强,从而能够提高含水层中污染物去除的效果。

It is a serious and common environmental problem that groundwater system is contaminated by petroleum hydrocarbons. A physical model, consisted of a tank with five types of unscreened sediments involving gravel, medium sand, fine sand, silt, and clay, was constructed at a pilot scale in the laboratory. With the functions of supplying, draining, monitoring, abstracting, injecting and so on, the aquifer model was used to study the natural removal of benzene, toluene, ethylbenzene and xylene (BTEX) in the aquifer by injecting gasoline. The results show that BTEX could be removed by natural attenuation including intrinsic biodegradation. Natural attenuation rates of soluble BTEX compounds were various. Rate of toluene ranged from 0.057 5 d-1 to 0.150 4 d-1, rate of xylene ranged from 0.068 3 d-1 to 0.104 6 d-1, rate of ethylbenzene was about 0.047 8 d-1 and rate of benzene ranged from 0.017 8 d-1 to 0.040 6 d-1. Toluene and xylene compounds were removed easily. Benzene, however, was relatively recalcitrant. As electric acceptors of intrinsic biodegradation, dissolved oxygen and nitrate showed the priority to be utilized, their concentrations decreased under the aerobic and anaerobic conditions in the experiment. Though sulfate is a usable electric acceptor, its concentration did not change in the experiment, suggesting that it was less utilized. With the decrease of BTEX concentrations and electric acceptors (dissolved oxygen and nitrate), it is suggested that intrinsic biodegradation has taken place in the aquifer under aerobic and nitrate-reducing conditions. In addition, this research shows that electric acceptor addition (e.g. nitrate) to the aquifer may enhance the ability of intrinsic biodegradation and may increase significantly the effectiveness for removing contaminants from the aquifer.