The purpose of this research is to evaluate chitin, a waste product from the shellfish industry, as a multifunctional substrate for passive treatment of acid mine drainage (AMD). Integral to the project is the integration of education and outreach. Chitin is an attractive substrate because of its potential to decrease acidity, increase alkalinity, and remove metals and its availability and low costs. Sacrificial microcosm tests will be used in the initial stage to rapidly assess the ability of chitin to achieve remediation of AMD waters of varying acidity and heavy metals contents. To develop an inventory of water chemistry changes throughout the life of the project, duplicate sets of samples beyond what is required for the microcosms will also be collected from one site each fall semester by Penn State students enrolled in the field methods course that will be developed. One set will be processed and analyzed by the Penn State students and the second set will be subject to a simplified set of analyses in partner high schools located in the Beech Creek, PA, watershed, which will be the location of the sampling sites. The second stage will consist of column studies that will be conducted to quantify sulfate reduction rates, metal removal capacities, substrate longevity, and the development and distribution of the microbial community when chitin is used as a barrier material for AMD treatment. Sorption isotherms will be used to evaluate the capacity of chitin for metal uptake. Comparative metagenomics will be used to compare the populations of organisms upstream, within the multiple points of the barrier, and downstream of the barrier and correlate that to chemical conditions and the effectiveness of treatment. Graduate students in the PI's lab will conduct the laboratory studies. In the last stage a field demonstration of a chitin barrier for the treatment of AMD at a site in the Beech Creek Watershed, PA, with the aid of the Beech Creek Watershed Association. The laboratory and inventory of water chemistry will inform the design and location of the field demonstration. Labor for the project installation will be provided by the graduate students in the PI's laboratory, students in the field methods class, high school students in the outreach program, and volunteer members of the Beech Creek Watershed Association. After the completion of the project, the system would continue to be monitored and used as a hands-on experimental station for AMD treatment by the PI's laboratory for as long as resources allow.
The course to be developed will fill the need at Penn State for a field methods class for remediation design by offering 1-hour of classroom instruction and 3-hours of field laboratory each week of the fall semester, and will cover the topics necessary to evaluate the health of surface and groundwater systems (including stream velocity measurements, sediment sampling, water quality sampling, basic water chemistry testing, invertebrate sampling, fish identification, and habitat assessment). In addition, students will learn basic design principles for constructing passive AMD treatment systems, and design their own system for one of the AMD creeks in the watershed. Every fall semester throughout the duration of the project, grade 11 students and a teacher from one of the high schools in the Beech Creek Watershed will pair with Penn State students to participate in two of the field class laboratories. Each year, one high school student will have the opportunity to continue learning about AMD research and field methods during an 8-week Summer Internship in the PI's laboratory.
Pyrite, a highly reactive rock commonly found in coal seams, is relatively harmless when undisturbed. But when pyrite (a.k.a. fool’s gold) is exposed to air and water, it leaches sulfuric acid, which in turn causes metals in the adjacent rocks and soil to be released. In Pennsylvania, that means iron, which is part of the pyrite itself, and aluminum and manganese, which are present in the soil. In other mining regions, the metals released can be even more dangerous—chromium, arsenic, even lead. Acidic drainage from abandoned mines continues to contaminate tens of thousands of miles of streams in the United States, including more than 5,000 miles in Pennsylvania. That makes Pennsylvania an ideal testing ground for innovative treatment technologies. With the support of an NSF Faculty Early Career Development (CAREER) Award, Dr. Rachel Brennan and her research team at Penn State University have tested a promising option for treating acid mine drainage: crab shell chitin, a waste product of the shellfish industry. One of the most abundant natural materials in the world, chitin is used to make paper, fabrics, weight-loss pills, and joint care supplements, among other products. In crustaceans like crab and shrimp, chitin combines with calcium carbonate, the same chemical that’s in limestone. Brennan’s research suggests that this combination may be extremely effective at cleaning up acid mine drainage. Detailed investigations in Brennan’s lab have shown that the treatment efficiency of crab shell is achieved by a combination of the reactivity of chitin-associated minerals (carbonates and phosphates) and the sorption capacity of chitin and its associated proteins. The intricate and complex structure formed by these three components results in a relatively high surface area compared to other common treatment materials. Chitin-associated minerals also appear to have a greater reactivity, aided by the release of organic compounds and phosphates. Biologically, crab shell can support more diverse microbial communities than traditional substrates, including a wide variety of sulfate reducing bacteria, which are the key players in AMD treatment systems. With this knowledge, Brennan’s team tested crab shell amended substrates at a site where other remedies have failed—the "high risk" Klondike-1 (KL-1) site in Cambria County, PA. Each liter of water at KL-1 contains 137 milligrams of iron and 382 milligrams of acidity, making it too strong to treat with conventional substrates like spent mushroom compost and limestone. In the laboratory, Brennan’s group tested different substrate combinations with crab shell to find the most cost-effective solution. Using preliminary designs developed by students in her NSF-supported "Field Methods for Remediation Design" class, Brennan's research team constructed pilot-scale vertical flow ponds with members of the local watershed association to field-test the technology. The team found that the treatment capacity, efficiency, and operational stability of the systems were improved when using crab shell amendments mixed with spent mushroom compost, thus allowing for a smaller treatment system to remediate equivalent volumes of AMD. Fundamentally, the results of this project provide insights into innovative passive treatment methods that can be used for remediating high strength AMD within small treatment footprints, at significantly lower cost than active treatment alternatives. The concepts developed here may serve as a model for the treatment of mixed waste systems using multifunctional substrates, to be examined in future work.
