Title: Passive Remediation of Acid Mine Drainage Using Chitin
Project Type: Research
Start Date: 03/01/2006
End Date: 02/28/2007
Congressional District: 5th
Focus Categories: Treatment, Water Quality, Geochemical Processes
Keywords: acid mine drainage, passive treatment, permeable reactive barriers, chitin, remediation, heavy metals, sulfate reducing bacteria, water quality
Principal Investigator: Brennan, Rachel A.
Federal Funds: $18,000
Non-Federal Matching Funds: $36,000
Abstract: Permeable reactive barriers and vertical flow wetlands are promising passive treatment systems for remediating the thousands of miles of streams that are contaminated by acidic, metal-laden drainage from abandoned mines throughout Appalachia and the western United States. The key to the effectiveness of these systems is the activity of sulfate reducing bacteria (SRB), which can reduce sulfate, increase alkalinity, and remove metals from affected waters if provided with an appropriate organic substrate. To keep costs low, fermentable waste materials like mulch, composted sewage sludge, and spent mushroom compost are often used as substrates; however, research has shown that under these circumstances the activity of SRB are often limited by a lack of available nitrogen. Consequently, passive treatment systems are often over-designed to compensate for low sulfate reduction rates. A nitrogen-containing substrate, such as chitin, is required to increase SRB activity and thereby decrease the size and cost of passive acid mine drainage (AMD) treatment systems.
Chitin, an abundant biopolymer that is found in the shells of crustaceans such as crab and shrimp, has several natural properties make it an ideal candidate for AMD treatment: upon fermentation it releases volatile fatty acids and nitrogen which can serve as substrates for sulfate reducing bacteria. In addition, the calcium carbonate found naturally in crab shells can serve as a buffer to increase alkalinity. Also, chitin maintains its permeability during degradation, which is critical quality in a permeable barrier treatment system. Finally, chitin is a waste material of the fishing industry, so availability is not limited and costs are low. In the proposed research, chitin is evaluated as an alternative substrate for AMD treatment in both microcosm tests and column experiments.
Sacrificial microcosm tests will be used to rapidly assess the ability of chitin to achieve remediation of AMD waters of varying acidity and heavy metals contents. Continuous-flow column studies will then be conducted to quantify sulfate reduction rates, metal removal capacities, substrate longevity, and optimal retention times when chitin is used as a barrier material for AMD treatment. For use in these experiments, AMD source water and benthic sediments will be collected from three to five representative sites throughout Pennsylvania. Microcosms containing AMD water, sediment, and chitin will be incubated and monitored until sulfate and metals concentrations are lowered to the maximum contaminant level (MCL). Then, AMD water will be pumped through columns packed with silica sand, benthic sediments, and chitin and monitored for 3 months or until sulfate and metals concentrations in the effluent are lowered to the MCL. At the conclusion of the experiment, the columns will be sacrificed and the sediment analyzed for precipitated metal concentrations as a function of distance through the columns.
Results from this study are expected to show that chitin is an effective substrate for AMD remediation, and that in the presence of chitin, pH increases, acidity decreases, and dissolved heavy metals concentrations decrease. A cost analysis is expected to show a significant cost savings when chitin is used as a substrate for passive treatment of AMD compared to the $15 billion estimated to be required to remediate AMD with other currently available technologies.
Progress/Completion Report, PDF