BIOAUGMENTATION FOR MTBE REMEDIATION - Bioaugmentation for Groundwater Remediation - page 283

CHAPTER 10
BIOAUGMENTATION FOR MTBE REMEDIATION
Cristin L. Bruce, 1 Joseph P. Salanitro, 2 Paul C. Johnson 3 and Gerard E. Spinnler 1
1 Shell Global Solutions (US) Inc., Houston, TX 77082; 2 University of Houston,
Houston, TX 77004; 3 Arizona State University, Tempe, AZ 85287
10.1 INTRODUCTION
Bioaugmentation for methyl tertiary butyl ether (MTBE; also known as methyl tert -butyl
ether) remediation has been of interest since the early 1990s (Novak et al., 1992 ). Research was
active for several years and several cultures were developed, tested and commercialized.
Interest has waned in recent years as it became apparent that bioaugmentation can be costly,
and generally is not needed for effective in situ treatment.
Bioaugmentation was initially considered because MTBE, and its cocontaminant and
primary daughter product tertiary butyl alcohol (TBA; also known as tert -butyl alcohol),
appeared recalcitrant to biodegradation in the subsurface. Biodegradation was slow and
often could not be demonstrated, at least in the early studies (Deeb et al., 2000 ; Schmidt
et al., 2004 ). MTBE has been reported to be biodegradable under a range of oxidation-reduction
potential (ORP) conditions. However TBA may not be biodegraded and therefore may accu-
mulate in some cases (McKelvie et al., 2007 ), though complete biodegradation of MTBE and
TBA has been observed in both aerobic and anaerobic studies (Finneran and Lovley, 2001 ).
Because MTBE generally has been found associated with petroleum hydrocarbons, which were
commonly treated by natural or enhanced aerobic in situ biodegradation, research focused on
developing cultures capable of complete aerobic biodegradation (i.e., mineralization) of MTBE
to carbon dioxide and water.
Given the widespread occurrence of MTBE in groundwater, research on bioaugmentation
cultures advanced quickly in different groups. Promising cultures were developed, and field
demonstrations were performed to test these aerobic cultures. In general, these demonstrations
indicated biostimulation alone was sufficient to treat MTBE contamination aerobically, as the
indigenous microorganisms adapted and were able to biodegrade MTBE under favorable
conditions. These results have pointed out valuable lessons for future bioaugmentation scenar-
ios for MTBE as well as for other compounds.
This chapter describes the scientific basis for bioaugmentation for MTBE remediation, and
some of the well documented field experiences with this strategy. In addition, it evaluates the
current status and future prospects for bioaugmentation for MTBE remediation.
10.2 MTBE USE AND OCCURRENCE IN GROUNDWATER
MTBE has been added to gasoline as an octane enhancer in the United States since about
1979, originally developed as an additive to replace tetra-ethyl lead. Ironically, its use was
promoted by regulators as a method to reduce air pollution due to gasoline emissions (McGarity,
2004 ). A 1990 Clean Air Act amendment mandated gasoline oxygen concentrations of 2.7%
weight to volume (w/v) fuel during cold months in areas with elevated levels of carbon monoxide