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Algal Bioremediation of the Berkeley Pit-Lake System – An In-Situ Test Using Limnocorrals
Primary Issue Addressed: Pit Lakes
Secondary Issues Addressed: Biological Treatment
Project Site: Berkeley Pit Lake, Butte, Montana
Collaborating Entities: Montana Tech and Montana Bureau of Mines and Geology
Cost Share: In-kind service provided by the Montana Bureau of Mines and Geology.
Project Description
The main objective of this project was to perform an in-situ field demonstration using limnocorrals to investigate the bioremediation potential of algae in the Berkeley Pit lake. A secondary objective is to ascertain the role that nutrification of the algae has on the bioremediation results.
Limnocorrals are an enclosed experimental apparatus, open at the top and closed at the bottom, used to simulate actual physical, chemical, and biological conditions of the lake environment within a controlled volume of water, allowing for biomanuipulation of one to several aspects of the natural environment. Manipulation in this experiment will consist of nitrification of limnocorrals using nitrate and phosphate concentrations to stimulate algal growth. It is postulated that if properly nutrified, dissolved metal concentration in the Berkeley Pit will decrease due to increasing algal biomass. Three replicate limnocorrals were set up, and nitrification was used as the variable. Specifically, one was nutrified with 5?mg/L nitrate and 2 mg/L phosphate, one was nutrified with 10 mg/L nitrate and 4 mg/L phosphate, and one was used as a control. The set of three was replicated three times (nine limnocorrals total). To document the importance of algal nutrification in bioremediation effectiveness, the nutrified limnocorrals were compared to non-nutrified limnocorrals and open water. An array of physical, chemical, and biological information has been collected. All variables were combined in a bioremediation matrix design using quantitative chemical analysis of samples to determine the interrelationships of the variable to each other at the end of the experiment.
Status
All data collection and interpretation has been completed for this project. Algal counts from the November 2004 sampling event indicated that nutrification increased algal counts. The level of nutrification had little effect on algal counts, but counts in nutrified limnocorrals were much higher than those in the control limnocorrals. Algal counts in the nutrified limnocorrals decreased with increasing depth. Bacteria counts increased with time in all limnocorrals, but neither depth nor level of nutrification played a role in bacteria counts. Pertaining to metal concentrations, time appeared to be the most significant factor having an effect within the limnocorrals. Depth and level of nutrification appeared to have no significant effect on the concentrations of any of the metals investigated. Arsenic and iron were the only two constituents that had a statistically significant change in concentration between July and November 2004 in response to the limnocorral treatments.
Project results are being assembled into the final report, which is expected to be completed in fiscal 2006.