Project Abstract

Evaluation of Strategies for Full Scale Bioremediation of the Seal Beach Site Using Anaerobic Microbial Processes

Principal Investigators

Martin Reinhard, Gary Hopkins, and Peter Kitanidis
Stanford University
E-mail: reinhard@stanford.edu

Goal

The goal of this project is to develop a plan for the remediation of the Seal Beach gasoline site using anaerobic microbial processes. Specifically, we are developing a hydraulic and process model for large-scale implementation of the processes we have been investigating in the laboratory, in pilot reactors and on a small field scale. By the end of this project year (September 1995) we will recommend a strategy for cleaning up large sections of the site based on the results of the field and laboratory studies and hydraulic modeling.

Rationale

Field and laboratory work has indicated that BTEX contamination can be removed biologically under anaerobic conditions using different electron acceptors or acceptor combinations. We have studied in detail nitrate- and sulfate-reducing and methanogenic conditions. All these conditions appear to have specific advantages and disadvantages and it appears that a combination of conditions could yield the best result. It is not clear, however, which of the possible electron acceptor combination should be chosen.

Approach

The approach has been to simulate different treatment options by releasing controlled amounts of BTEX compounds into a small test zone of the aquifer. The BTEX compounds were added to approximately 1000 L of water to which was added nitrate, sulfate, or carbonate salts as the electron acceptor. The water was then removed from the test zone in small batches and analyzed for BTEX compounds and nitrate and sulfate. Laboratory experiments were also conducted to explore the factors that affect BTEX degradation rate under anaerobic conditions.

Status

This project was completed in early 1995. Two sets of replicate release demonstrations under nitrate- (EO4 and EO5) and sulfate-reducing conditions (EO6 and EO7) were completed as was the first under methanogenic conditions (EO8). Under denitrifying-conditions toluene, m-xylene, and ethylbenzene were found to be rapidly degraded (within days) while o-xylene was degraded at a slower rate. The rate of benzene degradation was much slower but appeared to be significant. To evaluate the results of the controlled release demonstrations, a two-dimensional model for solute transport was developed and tested. The model is now being used to evaluate the aromatic degradation rate observed in the controlled release experiments and will serve as a basis for large scale implementation of the technology. Current efforts focus on the development of kinetic models to characterize contaminant transformation under various anaerobic conditions and to incorporate these kinetic models into the large-scale model. Large-scale models are being used for the design and interpretation of intermediate-scale controlled release experiments planned for the 1995/6 project year. For the future, we plan to develop a model more advanced than existing models and well-adjusted to represent the in-situ biodegradation of fuels in groundwater.