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2005 Progress Report: Reactive Transport Modeling of Metal Removal From Anaerobic Biozones

EPA Grant Number: R829515C010
Subproject: this is subproject number 010 , established and managed by the Center Director under grant R829515
(EPA does not fund or establish subprojects; EPA awards and manages the overall grant for this center).
Center: HSRC - Rocky Mountain Regional Hazardous Substance Research Center for Remediation of Mine Waste Sites
Center Director: Shackelford, Charles D.
Title: Reactive Transport Modeling of Metal Removal From Anaerobic Biozones
Investigators: Figueroa, Linda , Shackelford, Charles D. , Wildeman, Thomas
Institution: Colorado School of Mines , Colorado State University
EPA Project Officer: Lasat, Mitch
Project Period: October 1, 2003 through September 30, 2006
Project Period Covered by this Report: October 1, 2004 through September 30, 2005
RFA: Hazardous Substance Research Centers - HSRC (2001)
Research Category: Hazardous Waste/Remediation

Description:

Objective:

The objective of this research project is to develop and calibrate a model to describe the long-term microbial activity in anaerobic biozones. The investigators postulate that the proper design point for anaerobic biozones is characterized by the quasi-steady state that develops after 6 to 9 months of operation. Thus, calibration of the model based on the expected post start-up conditions is important. Post start-up conditions are characterized microbially by a balanced consortium of cellulolytic fermenters, sulfate reducers and methanogens, and substrate availability via the hydrolysis of complex organic polymers (e.g., cellulose).

Progress Summary:

A new mathematical model for the biochemical reactivity (“biomodule”) of the sulfate-reducing system has been developed, and coupled to the flow and transport models MODFLOW-2000 and RT3D v. 2.5. The primary biochemical processes encoded in this model include: (1) anaerobic bacterial decomposition of polysaccharides (cellulose-hemicellulose) releasing lactate; (2) sulfate reduction based on lactate; (3) precipitation of metal sulfides; (4) partial volatilization of hydrogen sulfide to the gas phase; and (5) reversible dissolution-precipitation of calcite (CaCO3(s)) and metal carbonates (e.g., siderite, FeCO3(s)). Additional model processes include sulfate reduction based on acetate, and competing lactate oxidation and methanogenesis. The mathematical model of biochemical reactivity has been calibrated and validated using quality experimental results from batch and column experiments obtained from the literature. Model parameter values were taken from the literature, and subsequently adjusted until model results provided good approximations of experimental results. Several sets of experimental results were employed, including four sets of batch experiments, two sets of column experiments, and three sets of bioreactor experiments. Batch and column experiments at the Colorado School of Mines (CSM) are generating data that will be used to modify a number of key kinetic parameters used in the above simulations. The inhibitory effect of mine water constituents on the rate-limiting step of cellulolytic fermenters (Cellulomonas flavigena) has been examined for zinc and copper in batch experiments. The rate and extent of cellulose degradation is a key parameter in predicting anaerobic longevity. Data from column experiments show that cellulose is not equally bioavailable in typical substrates used for anaerobic biozone construction. The cellulose-to-lignin ratio is one factor that is being examined to account for differential availability. Finally, the effect of the heterogeneous flow and transport domain on the performance of permeable reactive barriers (PRB) has been quantified using flow and particle tracking (MODFLOW-2000 and MODPATH 4.2). Probabilistic factors of safety for scaling the required extensions in PRB thickness and length as a result of aquifer heterogeneity were quantified in this component of the research. Also, values for the probabilistic factor of safety for scaling the PRB length (i.e., capture length ratio, or CLR) have been determined as a function of level of aquifer heterogeneity, aquifer correlation structure anisotropy, and distance from source zone to PRB.

Future Activities:

Future activities include calibrating the model against new batch and column testing data currently being collected at the CSM. Also, the Mine Waste Technology Program (MWTP) has approved funding for a field demonstration of sulfate reducing bioreactors using elements developed as part of two other Center projects and from previous MWTP research by MSE Technology Applications, Inc., in Butte, Montana. The drainage targeted is a neutral drainage without iron and thus previously encountered operational problems with iron precipitation using the Argo Tunnel mine water are avoided. The work plan includes collection of data sets that can be used for model validation. The field data collection will reflect temperature and metal variations over a 1.5-year period. The demonstration was scheduled to begin on March 1, 2005. Finally, samples of existing sulfate reducing bioreactor systems were provided by Golder Associates. The samples came from sites in diverse climates and at different system operational time periods. This year Amy Pruden and Linda Figueroa received supplemental funds from the U.S. Environmental Protection Agency (EPA) via David Reisman (EPA/ORD, Cincinnati) to collect samples from the same treatment systems. These samples are being analyzed for soluble carbohydrate, cellulose, and lignin composition. In addition, a fraction of these samples is being analyzed by Amy Pruden at Colorado State University for her continued evaluation of the critical microbial community structure in anaerobic biozones. This effort will generate additional field data that will be available for model calibration.

Supplemental Keywords:

bioremediation, contaminated sediments, acid mine drainage, acid mine runoff, anaerobic degradation, anaerobic microbial processes, biodegradation, contaminant transport, transport modeling, mining impacted watershed, permeable reactive barrier, sediment transport, sulfate reducing bacterium, , Industry Sectors, INTERNATIONAL COOPERATION, TREATMENT/CONTROL, Scientific Discipline, Waste, RFA, Remediation, Geology, Waste Treatment, Ecological Risk Assessment, Hazardous Waste, Environmental Engineering, Contaminated Sediments, Hazardous, Mining - NAIC 21, Bioremediation, heavy metals, risk assessment, runoff, treatment, transport models, biodegradation, microbial degradation, mining impacted watershed, redox, fate and transport modeling, contaminated waste sites, mining, mining wastes, stream ecosystems, acid mine runoff, suspended sediment, permeable reactive barrier, acid mine drainage, groundwater, metal removal, remediation technologies, contaminant transport, natural organic matter, anaerobic microbial processes, aquatic ecosystems, sediment transport, field monitoring, anaerobic degradation, sulfate reducing bacterium, treatment technology
Relevant Websites:

http://www.engr.colostate.edu/hsrc/ exit EPA

Progress and Final Reports:
2004 Progress Report
Original Abstract


Main Center Abstract and Reports:
R829515    HSRC - Rocky Mountain Regional Hazardous Substance Research Center for Remediation of Mine Waste Sites

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The 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.

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