DESIGNING A TRICHLOROETHENE SOURCE ZONE TREATMENT BASED UPON NANO SIZED ZERO VALENT IRON

CHSS的广泛使用为CHS进入地下土壤和岩石提供了无数机会，包括泄漏、储罐泄漏和故意处置。CHS的比密度大于1，这意味着CHS释放物有能力沉入地下水位以下。CHSS与水不相容，在水中的溶解度低。环境工程师和科学家将这类液体描述为DNAPL(稠密非水相液体)，以强调它们在水中的不混溶和大于1的比重。CHS DNAPL慢慢溶解在流动的地下水中，产生污染羽流。地下水提供了英国约40%的饮用水需求，CHS污染经常导致公共取水被放弃。这是不可持续的！因此，恢复受污染的含水层是可持续用水的一个必要方面。修复必须清除被捕获的CHS液滴和水池，这些水滴和水池不断滋养污染物羽流，并以某种形式遏制或降解羽流。铁可以通过还原脱氯作用将溶解的CHS分子降解为更安全的最终产品。然而，恢复含水层的可持续技术解决办法需要清除CHS DNAPL。这太难了！抽吸可能会移除一些DNAPL，但不是全部。这是由于泵送产生的力无法克服将CHS DNAPL捕获在孔隙空间中的毛细管力。在这些情况下，可以通过形成乳状液来去除大部分CHS质量。乳状液通常由表面活性剂稳定，但也可由胶体颗粒稳定。这种乳剂被称为皮克林乳剂。这一提议的基本前提是纳米铁颗粒可以用作乳液稳定剂。在英国皇家学会之前支持的一个项目中，我们能够证明，经过化学修饰的粘土颗粒可以作为Pickering乳状液从液体饱和多孔系统中去除被捕获的杂酚油。我们认为，化学修饰的nZVI可以用类似的方式去除CHS DNAPL。然而，通过乳液形成去除DNAPL的实验报告得出结论，并不是所有的DNAPL质量都被去除。这项建议涉及剩余物质的降解问题。现场观察表明，胶体大小的颗粒可以通过与表面的粘合接触从水相流场中去除。通常情况下，从治疗注射剂中去除乳状液稳定剂是一个问题。然而，我们推测，通过附着到捕获液滴的CHS/水界面(对乳状液形成的弹性)来去除nZVI将促进CHS的降解。此外，捕获在孔隙空间中的nZVI颗粒也会降解溶解的CHS。因此，我们相信，我们可以开发一种基于商业上可获得的廉价nZVI产品的技术，该产品可以通过使用相对廉价的两亲性分子进行化学修饰，在几个简单的步骤中可用于：(I)通过形成乳状液去除捕获的CHS DNAPL；(Ii)通过铁介导的还原脱氯降解捕获的CHS DNAPL(具有形成乳状液的弹性)；(Iii)降解溶解的CHS。这种处理方法将为CHS DNAPL污染含水层的恢复提供有效的技术解决方案。工作计划的目的是调查如何对nZVI进行化学修饰并随后部署以提供这一技术解决方案。

The widespread use of CHSs has provided countless opportunities for CHS entry into sub-surface soils and rocks through a combination of spillage, leaking storage tanks and deliberate disposal. CHSs have specific densities greater than 1 which means that a CHS release has the ability to sink below the water table. CHSs are immiscible with water and have low aqueous solubilities. Environmental engineers and scientists describe such liquids as DNAPLs (dense non-aqueous phase liquids) to emphasise their immiscibility in water and specific gravity, which is greater than 1. CHS DNAPLs slowly dissolve in flowing groundwater giving rise to a contaminant plume. Groundwater provides some 40% of the potable water needs of the UK and CHS contamination often results in public water abstractions being abandoned. This is unsustainable! Contaminated aquifer restoration is therefore a necessary aspect of sustainable water consumption. Restoration must entail the removal of trapped CHS droplets and pools which continuously feed the contaminant plume and some form of plume containment or degradation. Iron can be used to degrade dissolved CHS molecules to safer end-products through reductive dechlorination. However the sustainable technical solution to aquifer restoration requires the removal of CHS DNAPL. This is difficult! Pumping may remove some DNAPL but not all. This is due to the fact that the forces generated by pumping are unable to overcome the capillary forces that trap CHS DNAPL in pore spaces. In these cases much of the CHS mass can be removed via emulsion formation. Emulsions are usually stabilised by surfactants but they can be stabilised by colloidal particles. Such emulsions are called Pickering emulsions. The basic premise of this proposal is that iron nano-particles can be used as emulsion stabilisers. In a previously Royal Society supported project we were able to demonstrate that chemically modified clay particles could be used to remove trapped creosote from a liquid saturated porous system as a Pickering emulsion. We propose that chemically modified nZVI can be used to remove CHS DNAPLs in a similar fashion. However experimental reports of DNAPL removal via emulsion formation conclude that not all the DNAPL mass is removed. This proposal addresses the issue of degradation of the remaining mass. Field observation indicates that colloidal sized particles can be removed from the aqueous flow field through adhesive contact to surfaces. Normally the removal of emulsion stabiliser from a treatment injection is a problem. However we conjecture that the removal of nZVI by attachment to the CHS/water interface of trapped droplets (resilient to emulsion formation) will promote CHS degradation. Moreover nZVI particles trapped in pore spaces will also degrade dissolved CHS. We thus believe that we can develop a technology based upon the use of a commercially available inexpensive nZVI product which can be chemically modified by the use of relatively cheap amphiphilic molecules in a few straightforward steps that can be used to:(i) remove trapped CHS DNAPL through emulsion formation;(ii) degrade trapped CHS DNAPL (that is resilient to emulsion formation) through iron mediated reductive dechlorination;(iii) degrade dissolved CHS. Such a treatment will provide an effective technical solution to CHS DNAPL contaminated aquifer restoration. The purpose of the work plan is to investigate how nZVI can be chemically modified and subsequently deployed to provide this technical solution.