Exhaust gases from coal combustion contain contaminants such as sulfur dioxide (SO2) and nitrous oxide (NOx), and traces of other pollutants such as arsenic (As), mercury (Hg), nitrate (NO3), and selenium (Se). Exhaust gas scrubbers are used to limit the emissions of these constituents to air. Treating exhaust gases to remove SO2 is referred to as flue gas desulfurization (FGD), and the most common method is the use of wet scrubbers using limestone slurries. The limestone slurry is recycled multiple times in the scrubber, and to limit the concentration of dissolved constituents, a fraction of this solution is drawn off as a blowdown and becomes FGD wastewater. The treatment of this wastewater and its high-water demand has been recognized as a challenge by the US Department of Energy.
The major constituents in FGD wastewater include calcium (Ca), magnesium (Mg), sodium (Na), chloride (Cl), and sulfate (SO4). The research project focused on treating FGD wastewater using the newly proposed Mineral Recovery Enhanced Desalination (MRED) Process. Although the overall aim of the project was to develop the new treatment process, the focus of this of the study was on the recovery of commodities through selective chemical precipitation. For this purpose, a series of laboratory experiments were performed to examine the conditions under which solids could be precipitated from FGD wastewater along with the quality of solids and supernatant composition. The fate of As, Se, and NO3 in the treatment process was also investigated.
This research demonstrated that the MRED process is effective in treating the FGD wastewater, recovering water, and recovering high purity commodities such as magnesium hydroxide and gypsum. Hence, this provides additional benefits to coal-fired power plants by recovering commodities, avoiding disposal costs, and reducing water requirements by recycling treated wastewater. Furthermore, this process could also apply to wastewater with similar characteristics, such as brackish water.
Flue Gas Desulfurization Wastewater, Chemical Precipitation, Resource Recovery, Membrane Filtration, Ion Exchange, Nanofiltration
Department of Energy Grant # DE-FE0030584
Level of Degree
First Committee Member (Chair)
Dr. Kerry J Howe
Second Committee Member
Dr. Bruce M. Thomson
Third Committee Member
Dr. Abdul-Mehdi S. Ali
Tandukar, Sugam. "Recovery of gypsum & magnesium hydroxide from brackish water by chemical precipitation." (2019). https://digitalrepository.unm.edu/ce_etds/238