Using flue gas desulfurization gypsum to remove dissolved phosphorus from agricultural drainage waters

J Environ Qual. 2012 May-Jun;41(3):664-71. doi: 10.2134/jeq2011.0294.


High levels of accumulated phosphorus (P) in soils of the Delmarva Peninsula are a major source of dissolved P entering drainage ditches that empty into the Chesapeake Bay. The objective of this study was to design, construct, and monitor a within-ditch filter to remove dissolved P, thereby protecting receiving waters against P losses from upstream areas. In April 2007, 110 Mg of flue gas desulfurization (FGD) gypsum, a low-cost coal combustion product, was used as the reactive ingredient in a ditch filter. The ditch filter was monitored from 2007 to 2010, during which time 29 storm-induced flow events were characterized. For storm-induced flow, the event mean concentration efficiency for total dissolved P (TDP) removal for water passing through the gypsum bed was 73 ± 27% confidence interval (α = 0.05). The removal efficiency for storm-induced flow by the summation of load method was 65 ± 27% confidence interval (α = 0.05). Although chemically effective, the maximum observed hydraulic conductivity of FGD gypsum was 4 L s(-1), but it decreased over time to <1 L s(-1). When bypass flow and base flow were taken into consideration, the ditch filter removed approximately 22% of the TDP load over the 3.6-yr monitoring period. Due to maintenance and clean-out requirements, we conclude that ditch filtration using FGD gypsum is not practical at a farm scale. However, we propose an alternate design consisting of FGD gypsum-filled trenches parallel to the ditch to intercept and treat groundwater before it enters the ditch.

MeSH terms

  • Agriculture
  • Calcium Sulfate / chemistry*
  • Filtration / instrumentation*
  • Hazardous Substances / analysis
  • Metals, Heavy / chemistry
  • Phosphorus / chemistry*
  • Water Pollutants, Chemical / chemistry*
  • Water Purification / methods*


  • Hazardous Substances
  • Metals, Heavy
  • Water Pollutants, Chemical
  • Phosphorus
  • Calcium Sulfate