Impacts of flue gas desulfurization (FGD) gypsum in hypereutrophic waters

Abstract

Flue gas desulfurization (FGD) gypsum is a by-product of carbon-based energy sources that has been beneficially used as a component of concrete mixes and wallboard as well as in land-based agriculture as a soil amendment. In recent decades, FGD gypsum has started to be used in natural waters as a way to increase hardness, control phosphorus availability, and potentially mitigate eutrophication all due to the increase in calcium cations upon dissolution. These impacts have the potential for FGD gypsum to be used as an alternative management tool in hypereutrophic waters, such as aquaculture ponds. This research investigated the impacts of a much larger range of FGD gypsum concentrations than previously tested to determine if there were any negative impacts as concentrations increase and to ultimately find an optimal dose. Furthermore, this research aimed to test the optimal dose in a real-world whole pond setting at an active catfish aquaculture pond to determine its overall impacts and success in being used as a management tool in hypereutrophic waters. The results of this research found that as the concentration of FGD gypsum increases (upwards of 1,000 mg/L), you will start to see more negative impacts, such as a decrease in zooplankton biomass, a temporary increase in cyanobacteria, and select trace metal increases. A moderate dose, such as 500 mg/L, can control for algal growth while limiting these side effects. When used in hypereutrophic catfish ponds, this 500 mg/L dose can end up interacting with the nutrient-rich sediment causing a release of soluble reactive phosphorus and a subsequent spike in cyanobacterial abundance. Although FGD gypsum ultimately turned out to not provide the expected results seen in previous studies when used in hypereutrophic fishponds, it did not cause any trace metal contamination and could still potentially be used as a source of hardness with improved application methods.