Solar-Powered Remediation and pH Control

ER-201033

Objective

Many contaminants can be biodegraded by microbes that use hydrogen (H2) as an energy source, but bioremediation can be limited in low pH aquifers. Low pH aquifers that have been impacted with chlorinated solvents often have large contaminant plumes, and when degradation of tetrachloroethene (PCE) or trichloroethene (TCE) does occur at low pH, toxic cis-dichloroethene (cDCE) or vinyl chloride (VC) commonly accumulate. Low pH aquifers are common throughout the eastern United States, and treatment of these sites with buffers to increase groundwater pH is not feasible because of the large amount of buffer needed and the large size of many of the affected plumes. In other cases, contaminants accumulate in low permeability matrices or as free product (e.g., DNAPL) and become long-term sources of contamination that require prolonged and costly treatment. For these sites, an inexpensive and long-term source of electron donor (i.e., H2) to support in situ bioremediation is desirable. The objective of this project is to demonstrate a sustainable solar-powered system to support in situ biodegradation of Department of Defense (DoD) contaminants of concern and control aquifer pH.

Back to Top

Technology Description

This project will insert electrodes into PVC wells or directly into the ground in a chlorinated volatile organic compound (CVOC)-contaminated low pH aquifer. The electrodes will be operated to generate H2 to support biodegradation, and they will consume H+ and produce OH- to increase aquifer pH. The contaminated aquifer will be inoculated with a bioaugmentation culture to ensure that the appropriate microbes are present to support biodegradation. Electricity to operate the system will be provided by a solar cell and storage batteries. The project team will monitor pH changes; contaminant degradation; H2 production, distribution and utilization; electrode performance; and growth and distribution of CVOC-dehalogenating bacteria. Additional studies will include evaluation and modeling of factors controlling aquifer pH and the affect of hydrolysis and proton reduction on these factors; evaluation of potential electrode materials; evaluation and modeling of in situ H2 production, consumption and transport; and optimization of system operation parameters to evaluate suitability of the technology at a range of sites.

Back to Top

Benefits

At many sites, remediation of chlorinated solvents is complicated by naturally low pH. Successful demonstration of this technology will provide a cost-effective in situ treatment technology for remediating some of the most challenging DoD and Department of Energy contaminated sites and result in considerable cost savings. In addition to chlorinated solvent remediation, the technology should be suitable for any remedial objective that can be supported by H2-driven bioremediation, including treatment of energetic compounds, hexavalent chromium, ethylene dibromide (EDB), and perchlorate. It also will be suitable for prolonged treatment of sites where a persistent source of contaminant promises to create a long-term remediation problem (e.g., DNAPL sources or consolidated sediments) and for treating remote sites where accessing or maintaining electrical feeds is cost prohibitive. The technology is sustainable and does not require hydrocarbon-based energy input. (Anticipated Project Completion - 2013)

Back to Top

Points of Contact

Principal Investigator

Dr. Robert Steffan

CB&I Federal Services

Phone: 267-337-2005

Fax: 609-895-1858

Program Manager

Environmental Restoration

SERDP and ESTCP

Document Types

  • Fact Sheet - Brief project summary with links to related documents and points of contact.
  • Final Report - Comprehensive report for every completed SERDP and ESTCP project that contains all technical results.
  • Cost & Performance Report - Overview of ESTCP demonstration activities, results, and conclusions, standardized to facilitate implementation decisions.
  • Technical Report - Additional interim reports, laboratory reports, demonstration reports, and technology survey reports.
  • Guidance - Instructional information on technical topics such as protocols and user’s guides.
  • Workshop Report - Summary of workshop discussion and findings.
  • Multimedia - On demand videos, animations, and webcasts highlighting featured initiatives or technologies.
  • Model/Software - Computer programs and applications available for download.
  • Database - Digitally organized collection of data available to search and access.