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

CHS的广泛使用为CHS通过溢出、泄漏储罐和故意处置的组合进入次表层土壤和岩石提供了无数机会。CHS具有大于1的比密度，这意味着CHS释放具有下沉到地下水位以下的能力。CHS与水不混溶并且具有低的水溶解度。环境工程师和科学家将这种液体描述为DNAPLs（致密非水相液体），以强调它们在水中的不溶性和大于1的比重。CHS DNAPL在流动的地下水中缓慢溶解，产生污染物羽流。地下水提供了英国约40%的饮用水需求，CHS污染通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。恢复必须去除被捕获的CHS液滴和池，这些液滴和池不断供给污染物羽流，并进行某种形式的羽流遏制或降解。铁可用于通过还原脱氯将溶解的CHS分子降解为更安全的最终产物。然而，含水层恢复的可持续技术解决方案需要去除CHS DNAPL。这很难！泵送可以去除一些DNAPL，但不是全部。这是由于泵送产生的力不能克服将CHS DNAPL捕获在孔隙空间中的毛细力。在这些情况下，大部分的CHS质量可以通过乳液形成而除去。乳液通常由表面活性剂稳定，但它们也可以由胶体颗粒稳定。这种乳液称为皮克林乳液。该提议的基本前提是铁纳米颗粒可用作乳液稳定剂。在以前的皇家学会支持的项目中，我们能够证明，化学改性的粘土颗粒可用于从液体饱和的多孔系统中除去作为Pickering乳液的截留杂酚油。我们建议，化学修饰的nZVI可以用于以类似的方式去除CHS DNAPLs。然而，通过乳液形成去除DNAPL的实验报告得出结论，并非所有DNAPL物质都被去除。该提案解决了剩余质量退化的问题。现场观察表明，胶体大小的颗粒可以从水流场通过粘附接触表面。通常，从处理注射液中除去乳液稳定剂是一个问题。然而，我们推测，去除nZVI附着到CHS/水界面的被困液滴（弹性乳液形成）将促进CHS降解。此外，被捕获在孔隙空间中的nZVI颗粒也将降解溶解的CHS。因此，我们相信，我们可以开发一种基于使用市售廉价nZVI产品的技术，该产品可以通过使用相对便宜的两亲性分子在几个简单的步骤中进行化学改性，这些步骤可以用于：（i）通过乳液形成去除捕获的CHS DNAPL;（ii）通过铁介导的还原脱氯降解捕获的CHS DNAPL（其对乳液形成有弹性）;（iii）降解溶解的CHS。这种处理方法将为地下水DNAPL污染含水层的恢复提供一种有效的技术解决方案。该工作计划的目的是研究如何对nZVI进行化学修饰，并随后进行部署，以提供这种技术解决方案。

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.