-- A compost-free bioreactor system was installed in the spring of 2003. The system consists of a flow control weir, a pretreatment pond, two sulfate-reducing bioreactors, a settling pond, and an aeration channel.
-- Influent acid rock drainage (ARD) enters the system through a flow control weir. Sodium hydroxide is added to the influent to adjust the pH to approximately 4. Precipitates formed during the pH adjustment are settled out in the pretreatment pond. Ethanol is added to the ARD as it flows into a series of two sulfate-reducing bioreactors where sulfate is reduced to sulfide. Effluent from the bioreactors enters a settling pond where metal sulfide precipitates are removed. Finally, effluent from the settling pond flows through a rock lined aeration channel to promote gas exchange before being discharged into Aspen Creek.
-- Ethanol is contained in a 7,600 Liter (L) ethanol feed stock tank and sodium hydroxide is contained in three 3,800 L feed stock tank.
-- The system is designed to handle influent flows up to a maximum of 115 liter per minute (L/min). During the evaluation, inlet flows were evaluated up to 91 L/min.
-- The two bioreactors are lined with 60 mil high density polyethylene (HDPE) and filled with 20 to 40 centimeters (cm) of river rock.
-- The system operated in two modes: gravity flow mode and recirculation mode. The gravity flow mode operates by having the ARD pass through two successive sulfate-reducing bioreactors followed by precipitation of metal sulfides in the continuous flow settling pond. The recirculation mode operates by having ARD come into direct contact with the sulfide rich water from the bioreactors followed by precipitation of the metal sulfides in the settling pond. Also in the recirculation mode, a portion of the settling pond supernatant containing excess sulfate is then pumped back to the head of the bioreactors to generate additional sulfides.
Technology evaluated under the U.S. Environmental Protection Agency (EPA) SITE program
Edward Bates, EPA Project Manager
U.S. Environmental Protection Agency
National Risk Management Research Laboratory
Office of Research and Development
26 West Martin Luther King Jr. Drive
Cincinnati, OH 45268
Kevin Mayer, EPA Remedial Project Manager
U.S. Environmental Protection Agency Region 9
75 Hawthorne Street, SFD-7-2
San Francisco, CA 94105
Roy Thun, Project Manager
BP Atlantic Richfield Company
6 Centerpointe Drive, Room 6-164
La Palma, CA 90623
State of California Contact:
Richard Booth, Project Manager
California Regional Water Quality Control Board
2501 Lake Tahoe Blvd.
South Lake Tahoe, CA 96150
University of Nevada-Reno Contact:
Dr. Glenn Miller and Dr. Tim Tsukamoto
Department of Natural Resources and Environmental Science
University of Nevada-Reno, Mail Stop 199
Reno, NV 89557-0187
Average gravity flow mode influent ARD concentrations:
-- Heavy metals: Aluminum (Al) (37,467 ug/L), Copper (Cu) (691 ug/L), Iron (Fe) (117,167 ug/L), Nickel (Ni) (487 ug/L)
Average recirculation mode influent ARD concentrations:
-- Heavy metals: Al (40,029 ug/L), Cu (795 ug/L), Fe (115,785 ug/L), Ni (529 ug/L)
Copper and sulfur mining activities.
Type/Quantity of Media Treated:
From November 2003 to mid-May 2004 the system treated 9.24 million liters of ARD while in gravity flow mode. From mid-May 2004 to July 2005, 22.1 million liters of ARD were treated using the recirculation mode.
Purpose/Significance of Application:
The primary objectives of the SITE evaluation were to:
-- Determine the removal efficiencies for the primary target metals (Al, Cu, Fe, and Ni) over the evaluation period
-- Determine if the concentrations of the primary target metals in the treated effluent are below the interim (pre-risk assessment and record of decision) discharge standards mandated in 2002 Action Memorandum for Early Actions at Leviathan Mine
The secondary objectives of the evaluation were to:
-- Document operating parameters and assess critical operating conditions necessary to optimize system performance
-- Monitor the general chemical characteristics of the ARD water as it passes through the treatment system
-- Evaluate operational performance and efficiency of solids separation systems
-- Document solids transfer, dewatering, and disposal operations
-- Determine capital and operation and maintenance costs
-- Document winter operation procedures and effectiveness
-- Determine the volume and type of metal precipitate generated in the bioreactors and the optimal frequency and duration of bioreactor flushing
Regulatory Requirements/Cleanup Goals:
Maximum EPA Interim Discharge Standards:
-- Heavy Metals: Al (4,000 ug/L), Cu (26 ug/L), Fe (2,000 ug/L), Ni (840 ug/L)
The evaluation showed that the compost-free bioreactor system is effective in neutralizing acidity and reducing the concentrations of the heavy metal contamination to below the interim discharge standards. During the gravity flow mode, the system removed an average of 94 percent of the total heavy metal contamination from the ARD. The recirculation mode approach removed an average of 96 percent of the contamination. In addition, the metal sulfide precipitates created by the system were found to be non-hazardous, did not pose a threat to water quality, and could be used as a soil amendment for site reclamation.
The estimated initial fixed cost to construct a treatment system for the gravity flow mode was $836,617 and $864,119 for the recirculation mode system. These costs included site preparation, permitting, and capital and equipment costs. The site preparation costs included costs for system design, project and construction management, and preconstruction site work. The capital and equipment costs ($548,431 for gravity flow mode and $554,551 for recirculation mode) included costs for all equipment and materials used during construction, delivery of equipment and materials, earthwork, and initial system construction. The equipment and materials costs included costs for reagent storage tanks, pumps, valves, pond liners, rock substrate, pH control equipment, automation equipment and satellite phones for reliable communication at the remote site.
The total variable cost to operate the treatment system was $82,155 for gravity flow mode (over a 6-month period) and $75,877 for the recirculation mode (over a 16-month period). These costs include the cost of system startup and acclimation, consumable and rentals, labor, utilities, waste handling and disposal, analytical services, and maintenance and system modifications.
The Leviathan Mine is a former copper and sulfur mine located in Alpine County on the eastern slopes of the Sierra Nevada Mountain range. Mining activities since the 1860s have resulted in significant acid mine drainage (AMD) and ARD contamination. In the 1950s, approximately 22 million tons of overburden and waste rock were removed from the site's open pit mine and were placed in the Aspen Creek drainage channel.
In the spring of 2003 installation of a compost-free bioreactor at the site was completed. From November 2003 to July 2005 the treatment system was evaluated by the EPA SITE program to determine its effectiveness in treating ARD collected from the Aspen Seep.
The system operated in gravity flow mode from November 2003 through mid-May and in recirculation mode from mid-May through July 2005. During both periods the influent flow of ARD into the system ranged from 25 to 91 L/min. During gravity flow mode the system treated 9.24 million liters of ARD and during recirculation mode the system treated 22.1 million liters of ARD. The initial fixed cost to construct the treatment system for gravity flow mode is $836,617 and $864,119 for a recirculation mode system.
Results from the evaluation showed that the system was able to remove on an average 94 to 96 percent of the total heavy metal contamination from the ARD. Based on the success of the system, remediation of the ARD from the Aspen Seep continued.