Zuber, Eddie, Department of Civil and Environmental Engineering, Bucknell University, 1 Dent Drive, PA 17820, epz002@bucknell.edu; Higgins, Matthew, Department of Civil and Environmental Engineering, Bucknell University, 1 Dent Drive, Lewisburg, PA 17837, mhiggins@bucknell.edu.
The objective of this research was to precipitate and recover Fe and Al and trace metals (Co, Ni, Zn) from abandoned mine drainage (AMD) through pH adjustment. AMD samples were collected from ‘Site 15’ near Ranshaw, PA with pH values in the range of 3-5. Jar tests were used to evaluate metal removals at defined pH endpoints of approximately 5, 6, 7, 8, 9, and 10. NaOH was used to raise the pH in all experiments. The jar testing procedure included 10 minutes of rapid aeration, 30 minutes of mixing and flocculation, and 30 minutes of settling time. Metal concentrations were measured by ICP-MS. The results showed that the minimum pH value for greater than 90% removal of the metals was 7 for Fe, 6 for Al, 9 for Ni, 9 for Co, and 7 for Zn. A second set of experiments was conducted in which all the metals were precipitated simultaneously using a target pH of 9.0. The goal of this testing was to create a metal solution that could be used to supplement anaerobic digestion of food waste which typically requires addition of trace metals such as Co and Ni.
The final AMD precipitate supplemented anaerobic digestion (AD) of food waste, where methanogens require trace amounts of Fe and other metals to survive. AD reactors supplemented with AMD precipitate produced greater methane content than a control with no trace metal addition, but did not perform as well as a vendor supplied solution of trace metals designed for anaerobic digestion. Using AMD precipitate for AD of food waste potentially gives economic incentive to treating AMD, benefiting humans and the environment, but additional research is needed to fully develop this concept.
abandoned mine drainage, resource recovery, trace metals