Submitted to: Journal of Air and Waste Management Association
Publication Type: Peer reviewed journal
Publication Acceptance Date: 11/15/2011
Publication Date: 2/6/2012
Citation: Cheng, C., Chang, Y., Sistani, K.R., Wang, Y., Lu, W., Lin, C., Dong, J., Hu, C., Pan, W. 2012. Mercury Emission and Plant Uptake of Trace Elements during Early Stage of Soil Amendment Using Flue Gas Desulfurization Materials. Journal of Air and Waste Management Association. 62(2):139-150. Interpretive Summary: According to American Coal Ash Association, about 140 million metric tons of coal combustion by-products are produced annually. Among by-products, flue gas desulfurization (FGD) materials including FGD gypsum and waste by-products from dry and wet scrubbers are the fastest-growing in the United States due to the implementation of Clean Air Interstate Rule. Finding potential mass and environmental benign applications of FGD materials as an alternative to landfill disposal has been an ongoing efforts. Land application of FGD materials (e.g., soil amendment) has been considered as one of the possible mass usages. Preliminary studies have shown that FGD gypsum is able to improve the yield of crops by providing nutrients (e.g., calcium), changing soil physical properties, increasing water infiltration and storage, and reducing nutrient and sediment movement to surface water. However, only less than 2% of FGD gypsum is currently used for agricultural purposes. The presence of trace elements (e.g., mercury (Hg), arsenic (As), boron (B), and selenium (Se)) in FGD materials with elevated concentration levels has been the concern. A pilot-scale field investigation was carried out to determine the distribution of Hg in the three potential mitigation pathways, emission to air, uptake by plants, and leaching. Results show the amounts of Hg released into the air and uptake in grass from all FGD treated plots were higher than the untreated soil. No Hg was detected in the leachate water collected during the only 3-hour, 1-inch rainfall event.
Technical Abstract: A pilot-scale field study was carried out to investigate the distribution of Hg and other selected elements in the three potential mitigation pathways, i.e., emission to ambient air, uptake by surface vegetation (i.e., grass), and rainfall infiltration, after flue gas desulfurization (FGD) material is applied to soil. Three FGD materials collected from different FGD processes were used. Results show the amounts of Hg released into the air and uptake in grass from all FGD material-treated plots were all higher (P<0.1) than the amounts observed from untreated soil. Hg in the soil amended with the FGD material collected from a natural oxidation wet scrubber (i.e., SNO) more readily released to air comparing to the other two FGD materials collected from the synthetic gypsum dewatering vacuum belt (i.e., AFO-gypsum) and the waste water treatment plant (i.e., AFO-CPS) of a forced oxidation FGD system. Larger portion of Hg added to soil as a result of SNO amendment released to the air (28.8%) comparing to the amount uptake in grass (1.8%). Less than 1.4% and 0.3% of total added Hg released from the AFO-gypsum (0.81% by emission and 0.56% by grass uptake) and AFO-CPS (0.02% by emission and 0.28% by grass uptake) treated plots, respectively. No Hg was detected in the available infiltrations collected during the only 3-hour, 1-inch rainfall event occurred throughout the 4-week testing period. To compare release potentials of trace elements from soils treated with the three different FGD materials, two parameters were calculated to provide comparisons based on the unit weight of the material and the corresponding energy production rate of the respective power plants where the FGD materials were collected from. In addition to the pilot scale field study, two series of laboratory scale greenhouse experiments were carried out to investigate the effects of applying dosage, soil moisture, and types of applying FGD materials on Hg emission.