人工注气及生物产气对孔隙介质中DNAPL运移影响

重非水相液体(DNAPLs)的污染和治理问题是国内外研究热点,由地下水曝气技术注入的人工气体或生物作用等产生的气体必然对DNAPL在地下水系统中的运移及修复产生影响.采用CCD实时监测系统,以TCE为目标污染物,通过3个二维砂箱试验,以饱水条件下DNAPL的运移为对照,研究了人工注气及生物产气对DNAPL在孔隙介质中运移的影响.结果表明:(1)基于CCD相机的透射光监测系统是一种研究二维孔隙介质中多相流迁移规律的有效非侵入式监测方法,应用于实时监测水/NAPL,水/气,水/NAPL/气多相系统中流体渗流过程.(2)人工注气和生物产气两种条件下,气体在多孔介质中的分布特征有差异,前一条件下气体连续分布,后一条件下则以非连续分布的气泡为主.(3)在水/气两相系统中,气体的存在使得DNAPL污染羽的整体形状更加不规则;同时缩短了TCE污染羽前缘整体平均垂向下迁距离;也导致迁移路径上孔隙中TCE的截留量变小.DNAPL的入渗过程受重力影响以垂向渗流为主,垂向渗流时易于驱替孔隙中的水分,然而水平渗流时优先驱替孔隙中的空气.

The impact of aeration or biogenic gas on DNAPL's migration in porous media

Research on the contamination and remediation of Dense Non-Aqueous Phase Liquids(DNAPLs) has become the hot field. The aeration or biogenic gas produced by microbes has an impact on the migration and remediation of DNAPL in the groundwater system. Using a CCD real-time monitoring technology, TCE was selected as the target pollutant and then three two-dimensional sandbox experiments were carried out. In comparison to the migration of DNAPL in the saturated porous media, the migration under air and biogenic gas condition have been studied. The results show that:1 The transmission light monitoring system based on a CCD camera is an effective and non intrusive method to study multi-phase flow in 2-D porous media, and real-time monitoring of the fluid infiltration process in multiphase system including Water/NAPL, Water/Gas, Water/NAPL/Gas. 2gas distribution in porous media is different between air and biogenic gas condition:air was mainly continuously distributed, while biogenic gas was mainly existed in the form of discontinuous bubbles. 3 In Water/Gas system, the overall shapes of the DNAPL plume become more irregular under two gas conditions; while the overall average distance of TCE plume front was shorten by the air; the intercepted amount of TCE during the migration also became smaller under both two gas conditions. The infiltration of DNAPL is mainly influenced by gravity in the three-phase system. TCE is more prone to displace water of the pores towards the vertical direction, while TCE displaces air in priority towards the horizontal direction.