Phytoremediation Rhizoremediation
The first part of Volume 9 will supply the readers with up-to-date information concerning the necessary theoretical background, both concerning removal of heavy metals from the contaminated environment, and removal, detoxication and even degradation of to
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1. Introduction Many volatile organic compounds pose a unique type of threat to our environment, existing over vast areas in multiple media: water, soil and vapour. Phytoremediation applications are also unique as they are both highly visible and publicly acceptable and are also both long-term and low-energy to apply. These attribute pairings are quite unusual, being mutually exclusive for all other remedial approaches. The other attribute that is unmatched by any other technology is the ability to concurrently remediate and ecologically restore the environment. The listed phytoremediation traits do not yet include: rapid, highly effective, or well understood. Research and engineering findings covered herein address these concerns and reveal how and why phytoremediation can offer an unmatched possibilities to treat volatile organic compounds in particular. Numerous contaminants are classified as ‘volatile organic compounds’ that are commonly referred to as VOCs. The definition of a VOC is generally a compound that has a vapour pressure of greater than 0.1 mm of mercury. As this definition is broad and only considers one chemical property, the term VOC in this work specifically refers to research performed on chlorinated solvents and a number of petroleum hydrocarbons. The extensive use as solvents and fuels lead to widespread releases through spills and leaks in the handling and transport due to the immense volumes. Additionally, in previous decades these compounds were disposed via methods that are quite improper in light of today’s knowledge, but at the time simple dumping on unused land or even dumping out of the back door of a dry cleaner or automechanic shop were common disposal practices and accepted. Release to the environment occurred in almost all places where these compounds were used. The inherent physico-chemical properties that made these compounds so desirable are the same properties that make these compounds a bane to current efforts to address the earlier releases. The chlorinated solvents are particularly problematic because these compounds with low reactivity, relatively low water solubility, dense liquid phases, and high volatility now pose large dissolved groundwater plumes with overlying vapour contamination of the vadose (unsaturated) zones, and pools of pure compounds that are difficult to access. Large enduring plumes of these compounds are difficult to address, even though decades of effort were spent to remediate contaminated environments.
199 M. Mackova et al. (ed.), Phytoremediation Rhizoremediation, 199– 216. © 2006 Springer.
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Joel G. Burken and Xingmao Ma
Current remedial approaches for VOC-contaminated groundwater and unsaturated zones include: air sparging, vacuum-enhanced recovery, aqueous pump and treat, in situ chemical reactions (reduction or oxidation), in-situ bioremediation (microbial-based), permeable reactive barriers, and almost all conceivable combinations of these and even a few other technologies. Many of these technologies are certainly effective at removing and
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