Coal ash is the solid waste generated during coal combustion and includes fly ash, bottom ash, and sludge from flue gas desulfurization units. In the United States, the combustion of coal generates more than 100 million tons of coal ash each year. Half of these wastes is reused for beneficial purposes such as the manufacture of concrete and other construction materials. Coal ash is also enriched in leachable trace elements such as arsenic, selenium, and boron that can be harmful to ecosystems near coal ash disposal sites. The practice of disposing coal ash in holding ponds has received much attention over the last decade after the catastrophic failures of ash ponds in Tennessee (2008) and in North Carolina (2014). The magnitude of these spills and the uncertain environmental costs have renewed efforts to improve policies for coal ash disposal and identify beneficial reuse opportunities.
Objectives of coal ash research in the Hsu-Kim group are two-fold: 1) To delineate the chemical forms of potentially toxic trace elements such as arsenic and selenium in various types of coal ash residuals; and 2) To understand how the chemical form of these elements as well as ash storage conditions influence the mobility and transformations of these elements. Our work has focused on the role of biogeochemical redox gradients for controlling solubility of arsenic and selenium as well as biotransformation of mercury. We also examine the influence of other factors that influence coal ash composition, such as feed coal characteristics and conditions during combustion and residuals collection.
This research is supported by the National Science Foundation and the Department of Energy.
Water Quality in North Carolina lakes: ES&T 2012
Trace Element & Isotope Geochemistry: ES&T Selenium (2013), B and Sr (2014), Radioactivity (2015), Influence of redox for Se and As (Applied Geochem 2016) and for mercury (ESPI 2016)
Selected publications on trace element geochemistry in coal ash and coal ash spill sites:
Rivera, N.A., F.T. Ling, Z. Jin, A. Pattammattel, H. Yan, Y.S. Chu, C.A. Peters, and H. Hsu-Kim. Nanoscale heterogeneity of arsenic and selenium species in coal fly ash particles: analysis using enhanced spectroscopic imaging and speciation techniques. Environmental Science: Nano 10, 768–77. https://doi.org/10.1039/d2en01056a
Jin, Z., J. Ren, N. A. Rivera, J. C. Hower, and H. Hsu-Kim. “Functional Predictor Variables for the Leaching Potential of Arsenic and Selenium from Coal Fly Ash.” ACS ES&T Water, 3, 1105–15. https://doi.org/10.1021/acsestwater.2c00568.
Schwartz, G.E.; Hower, J.C.; Phillips, A.L.; Rivera, N.; Vengosh, A.; Hsu-Kim H. (2018). Ranking coal ash materials for their potential to leach arsenic and selenium: The relative importance of ash chemistry and site biogeochemistry. Environmental Engineering Science. DOI: 10.1089/ees.2017.0347 (open access)
Schwartz, G.E.; Redfern, L.K; Ikuma, K.; Gunsch, C.K.; Ruhl, L.S.; Vengosh, A.; Hsu-Kim, H. (2016). Impacts of coal ash on methylmercury production and the methylating microbial community in anaerobic sediment slurries. Environ. Sci.: Processes & Impacts. 18, 1427-1439. DOI: 10.1039/C6EM00458J
Schwartz, G.E.; Rivera, N.A.; Lee, S.-W.; Harrington, J.M.; Hower, J.C.; Levine, K.E.; Vengosh, A.; Hsu-Kim, H. (2016). Leaching potential and redox transformations of arsenic and selenium in sediment microcosms with fly ash. Applied Geochemistry. 67, 177-185. DOI: 10.1016/j.apgeochem.2016.02.013.
Liu, Y,-T.; Chen, T.-Y.; Mackebee, W.G.; Ruhl, L.; Vengosh, A.; Hsu-Kim, H. (2013). Selenium Speciation in Coal Ash Spilled at the Tennessee Valley Authority Kingston Site. Environ. Sci. & Technol. 47(24), 14001-14009. DOI: 10.1021/es4041557.
Bartov G., Deonarine A., Johnson T.M., Ruhl L., Vengosh A., Hsu-Kim H. (2013). Environmental impacts of the Tennessee Valley Authority Kingston coal ash spill. 1. Source apportionment using mercury stable isotopes. Envir. Sci & Technol. 47(4), 2092-2099. DOI: 10.1021/es303111p.
Deonarine A., Bartov G., Johnson T.M., Ruhl L., Vengosh A., Hsu-Kim H. (2013). Environmental impacts of the Tennessee Valley Authority Kingston coal ash spill. 2. Effect of coal ash on methylmercury in historically contaminated river sediments. Envir. Sci & Technol. 47(4), 2100-2108. DOI: 10.1021/es303639d.
Ruhl L., Vengosh A., Dwyer G., Hsu-Kim H., Schwartz G., Romanski A., Smith S.D. (2012). The impact of coal combustion residue effluent on water resources: a North Carolina example. Envir. Sci & Technol. 46(21), 12226–12233. DOI: 10.1021/es303263x.