Grantee Research Project Results
Final Report: High-Performance Electrolysis for In-Situ Remediation of Heavy Metals
EPA Contract Number: 68D98123Title: High-Performance Electrolysis for In-Situ Remediation of Heavy Metals
Investigators: Exner, Jurgen H.
Small Business: Environmental Chemical Corporation
EPA Contact: Richards, April
Phase: I
Project Period: September 1, 1998 through March 1, 1999
Project Amount: $70,000
RFA: Small Business Innovation Research (SBIR) - Phase I (1998) RFA Text | Recipients Lists
Research Category: Hazardous Waste/Remediation , SBIR - Waste , Small Business Innovation Research (SBIR)
Summary/Accomplishments (Outputs/Outcomes):
Introduction. Contamination of soil and groundwater by heavy metal ions, such as cadmium, copper, lead, mercury, chromium, and arsenic, is a widespread problem and of a global scale. Heavy metals have entered the environment in the past from industry through the direct disposal onto soil or through discharges into water. Facilities from electronics and metal-plating operations, photographic processing, and mining were and are today the principal sources. Heavy metals pose a significant hazard to the environment and human health.Objectives. The overall objective of this work is to develop a treatment process for removing heavy metal ions from groundwater using novel electrode materials for electroplating. This innovative process is to have the following benefits:
In situ application, groundwater treatment without removal of ground water
from the aquifer,
Achievement of MCL treatment standards,
Economic
advantage over the baseline technology, pump-and-treat, precipitation, phase
separation, and solids disposal,
Recovery of metals for possible recycle,
Operation with minimal attention and maintenance,
Other potential market
applications such as mine drainage wastes and in situ soil flushing,
Combination with other treatment technologies for achievement of
site-specific treatment objectives.
In this in situ design concept, groundwater enters the well through a screen at the bottom of the contaminated aquifer, is pumped through a replaceable electrolysis cell, and leaves the well at a screen near the vadose/groundwater interface. Groundwater follows a toroidal flow path, flushes adsorbed and dissolved contaminants from the aquifer, and reenters the intake, as illustrated in Figure 1.
The specific technical objectives of Phase I of this project were to:
1. Evaluate the feasibility of reducing metals in simulated, low conductance groundwater to the ppb range by using electrochemical cells with high-surface-area (HSA) cathodes.
2. Obtain treatability data for three heavy metal ions, copper, cadmium, and mercury. Determine current density/current efficiency relationships and rates of metal removal for single metals and for mixtures of metal ions.
3. Evaluate the impact on electrode performance of common waste constituents such as iron, anions such as chlorides and carbonates, and surfactants and chelants. Use the results to understand future field results and to expand the application of this method to in situ soil flushing and mine wastes.
4. Test waste from a contaminated site at conditions defined by preliminary results.
5. Evaluate the commercialization potential by using the laboratory data to define further the anticipated flow rates and reactor size necessary to address probable market segments. Define further the cost and competitive standing of the process relative to baseline technologies.
Results. Laboratory-scale tests were carried out in batch-recycle reactors with four different HSA electrodes. The rates of electrodeposition of copper, cadmium, and mercury from low ionic strength, simulated groundwater were tested as a function of current density, pH, ionic strength, flow rate, and electrochemical cell design by removing and analyzing samples by inductively coupled plasma emission spectrophotometry (ICP) at selected times.
Copper and cadmium ion solutions were reduced to less than 0.01 mg/L at current densities of 179-286 amperes/m2 (A/m2) in reasonable time frames. Mercury ions were reduced to 0.04 mg/L. In the laboratory reactor, copper, cadmium, and mercury removal rates of 79 mg/ampere-hour (A-hr), 25 mg/A-hr, and 33 mg/A-hr, respectively, in the concentration range of 100-0.01 mg/L. In experiments simulating groundwater conditions, deposition rates decreased with decreasing ionic strength and decreased slightly with added ferrous and chloride ions. Results indicate that treatability testing of waste streams will be necessary. Treatment of an actual waste stream from mine drainage confirmed the results of the work with simulated groundwater solutions.
Conclusions. The results allowed the conceptual design of an HSA electrochemical cell that can be placed into a groundwater recirculation well. Preliminary economic evaluations indicate that such a process can be less costly than the baseline technology, pump-and-treat with precipitation. The process allows combination with treatment trains, such as in situ stripping of volatile organic compounds, and economic optimization with specialized adsorption resins.
Commercialization Potential. The primary markets for the technology are metal-contaminated groundwater, acid mine drainage, and in situ soil flushing. These markets are huge and the key to success for the HSA electrodeposition technology will be identification of specific problem sites in which the technology is effective, competitive with standard treatment processes, and acceptable for the specific site condition.
The market for groundwater restoration is enormous. Metal contamination may affect about 22,500 sites in the U.S., and about 70 % of these require groundwater treatment. The total volume of metal-contaminated groundwater probably exceeds several hundred billion gallons. The HSA electrodeposition process will be applicable and competitive with other technologies at a fraction of the sites. Conservative assumptions of 0.1 % of the sites suggests a yearly revenue from product sales of about $15 million within ten years of market introduction. Remediation itself will draw in similar revenues.
An estimated 200,000 inactive mines exist in the Western U. S. Mine drainage from such sites varies from 1-1,000 gpm, and the composition varies widely. Even a very small fraction of these sites leads to a considerable quantity of water that could be treated by this process. The third market involves soil remediation by in situ flushing. Again, there are a huge number of potential sites, but only a fraction of these will be suitable for in situ flushing. Soil flushing of metal-contaminated soil can be effective when chelating agents are added to the flushing solution. The HSA electrodeposition process may allow recovery of these expensive chelates and make soil flushing a competitive remediation process.
Technical work in Phase II will focus on optimizing surface area characteristics of three-dimensional electrodes and on testing electrodeposition of other plateable metals. In addition, a cell will be constructed and tested in long-term experiments to obtain appropriate mass balances. Sites with metal-contaminated groundwater or acid mine leachate will be identified and field testing will be carried out.
Supplemental Keywords:
Scientific Discipline, Economic, Social, & Behavioral Science Research Program, Toxics, Waste, Water, National Recommended Water Quality, Physics, Contaminated Sediments, Remediation, Wastewater, Chemistry, Engineering, 33/50, Groundwater remediation, Engineering, Chemistry, & Physics, Economics & Decision Making, Mercury, electrochemical technology, cadmium & cadmium compounds, in situ remediation, soil and groundwater remediation, soil sediment, measuring benefits, lead & lead compounds, lead, cost benefit, contaminated soil, soils, soil and groudwater remediation, soil remediation, mercury & mercury compounds, copper, groundwater contamination, cadmium, heavy metal contamination, groundwater, heavy metals, electrochemical methods, electrochemical treatment, aqueous waste streamThe perspectives, information and conclusions conveyed in research project abstracts, progress reports, final reports, journal abstracts and journal publications convey the viewpoints of the principal investigator and may not represent the views and policies of ORD and EPA. Conclusions drawn by the principal investigators have not been reviewed by the Agency.