Flue gas desulfurization gypsum as a sustainable amendment for coal mine soil reclamation and camelina-based bioenergy crop production

Flue gas desulfurization (FGD) gypsum, a byproduct of the chemical cleaning of FGD wastewater in coal-fired thermal electricity power plants, poses substantial environmental challenges, as it contains trace amounts of heavy metals and metalloids. In this study, we explored the potential use of FGD gypsum as a sustainable soil amendment to rehabilitate degraded coal mine soils and promote the cultivation of the bioenergy crop camelina (Camelina sativa). The sulfur content in FGD gypsum promoted glutathione and phytochelatin biosynthesis, enhancing heavy metal stress tolerance in camelina. Adding FGD gypsum to the soil improved camelina growth by reducing heavy metal toxicity, supporting photosynthesis, and increasing seed yield, while also extending the vegetative growth period from 85 days when grown in agricultural soil to 110-115 days. This treatment also enhanced the biosynthesis of the amino acids glutamic acid and proline, which are crucial for stress resilience. The application of lime rapidly increased soil pH from 4.6 to 6.9, helping initial seedlings establishment. However, lime amendment led to the bioaccumulation of mercury in seeds (0.34 mg/kg). In contrast, no detectable mercury was found in seeds from plants grown in soils amended with FGD gypsum, confirmed by inductively coupled plasma-mass spectrometry (ICP-MS). Moreover, soils amended with FGD gypsum produced seeds enriched with desirable fatty acids, such as oleic acid, for bioenergy applications, offering a cost-effective alternative to lime. These results illustrate the environmental benefits of utilizing FGD gypsum as a soil amendment and for sustainable camelina-based bioenergy production on abandoned coal mine lands.