Lyn Bobincheck and Dr. W. Vincent Wilding, Chemical Engineering
Contaminated groundwater results from uncontrolled release of wastes such as fuel and industrial solvents. This contamination is cleaned up through several methods including bioremediation. Current methods of bioremediation include traditional pump and treat, bioventing, and bio-walls. Bio-walls are a new, promising technology described by several researchers.1,2 The purpose of this research was to determine the state of the art bio-wall technology, and to present a bio-wall design which optimizes necessary parameters for bioremediation.
Literature searches were conducted and several interesting studies were found. It was discovered by researchers at the University of Waterloo that zero-valent iron could reduce chlorinated compounds. The chlorinated compounds reacted to form the corresponding hydrocarbon and chlorine ions.3 The zero-valent iron was incorporated into a system called the “funnel-and-gate,” where contaminated groundwater is directed through a gate of reactive iron by impermeable funnels.4 (See Figure 1) Another study involved pulsing nutrients needed to stimulate bioremediation through a permeable wall. The wall is saturated with nutrient, and as the groundwater flows through the wall, nutrients are taken into the groundwater.5 Studies were also found where an in-situ bioreactor was installed in groundwater to facilitate removal of agricultural chemicals from the Soil.
While I was conducting the literature searches, it became very apparent that the University of Waterloo in Ontario Canada was very active in the area of bio-wall research. I saw an advertisement for a short course they were sponsoring entitled “Technologies for Intrinsic and Semi-Passive In Situ Remediation of Groundwater.” The course was to cover the design, installation, and performance of in-situ bio-walls, including the funnel-and-gate system. This conference was to cover the topics that I had proposed for this research, and so I attended the course. The conference was very informative because the researchers who had developed the systems were the lecturers. During the course we visited the Canadian Forces Base at Borden, where Waterloo conducts all of their experiments.
The University of Waterloo had developed several funnel-and-gate systems to optimize remediation of contaminants. The direction of this research is to use gates in parallel to treat mixed contaminant plumes. There were two projects in which these systems were being demonstrated. The first project is a funnel and gate system with three gates in series. (See Figure 1) The three gates in this system each contained a different method for remediation. The first gate held iron filings to remediate chlorinated compounds, followed by an oxygen release compounds suspended in water to breakdown the remaining hydrocarbons. The second gate was a control gate with no active remediation occurring. The third gate had a pulse injection well to stimulate anaerobic bioremediation of the chlorinated solvents, followed by a biosparge gate to create conditions for aerobic remediation. Results from the study are not yet available because the contaminants which have been injected for remediation have not moved far enough downgradient to contact the bio-walls. The second project was being installed the day we visited the site. The system contains four gates in parallel to promote anaerobic bioremediation. The first gate contains nitrate briquettes, followed by two gates of granular activated carbon, with the fourth gate initially empty.
It is evident from these research projects that the state of the art in bio-walls is a staged reactor. This is necessary because rarely does a site only contain one contaminant that must be removed. Often sites have several different compounds that will not remediate with the same technique.
However, for sites that contain similar compounds or contaminants that can be remediated with the same technique, another promising technology was presented. Unpumped wells are used to inject nutrients, such as oxygen, to stimulate bioremediation. The studies presented used ORC© within the wells to release oxygen. ORC© is a solid which releases oxygen when contacted with water. This compound was placed into “socks” and sunk into the wells. The socks released oxygen over time and effectively remediated hydrocarbons.
For further research, the unpumped wells provide several opportunities. Currently, unpumped wells are only being used for nutrient release, but another potential use for these wells is as an insitu bioreactor. This use of wells is in concept stages, with design parameters to be determined. This is the next step for this research. While I did not reach the design stage of the projects, I was able to talk to the researchers developing bio-walls, and also saw how they install and build the walls. I learned what has been accomplished and can build on their successes and knowledge. I feel that what I learned by attending the conference was invaluable to current and future research.
References
- X. Yang, et. al. 1995. AIChE Summer National Meeting, Conference Papers.
- D.W. Blowes, et al. 1994. Geotechnical Special Publication 1588-1607
- R.W. Gillham and S.F. O’Hannesin. 1994. Ground Water 32: 958-967.
- R.C. Starr and J.A. Cherry. 1994. Ground Water 32: 465-476.
- J.F. Devlin and J.F. Barker. 1994. Ground Water 32: 374-380
- D.W. Blowes, et al. 1994. Journal of Contaminant Hydrology 15: 207-22 1. 12