The U.S. EPA’s proposed revisions to a 2015 rule regarding electric power plant waste discharges bring both opportunities to expand technology being developed at Ohio State as well as concerns about extended deadlines and less stringent requirements for retiring facilities.
Last month, the U.S. EPA proposed revisions to the Steam Electric Effluent Guidelines and released them for public comment.
The EPA estimates that its proposed rule would result in compliance cost savings of more than $175 million pre-tax annually while reducing the amount of pollutants discharged to our nation’s waters by approximately 100 million pounds per year over the existing regulation.
The most significant among the regulatory options in the 2019 revision includes new technology-based limitations for two types of power plant waste streams: waste water from flue-gas desulfurization (FGD), which is a process used to remove sulfur dioxide from fossil fuel burning plants, and bottom ash transportation water, or discharged water that transports non-combustion residue from the plants to impoundment sites like landfills.
One option the EPA recommends for plants to comply with the rules is biological technology, which chooses microorganisms specifically for use in FGD systems to remove selenium, nitrate-nitrite, mercury and other pollutants. The microorganisms convert these pollutants to non-toxic forms and incorporate them within the system.
Another option deemed a “Best Available Technology Economically Achievable” by the EPA is an emerging technology, membrane filtration (i.e., nanofiltration, reverse osmosis and forward osmosis).
The EPA recognizes that membrane filtration still has many uncertainties, such as membrane fouling and handling of the concentrated brine. However, considering that membrane filtration is the only technology option that is effective in removing all regulated pollutants and that can be developed into a zero-liquid-discharge system for coal-fired power plants, the revision provides an excellent opportunity for the technology to be fully developed into a feasible treatment option for the FGD wastewater.
For example, the research team led by Linda Weavers, professor of civil, environmental and geodetic engineering and co-director of the Ohio Water Resources Center, has been investigating a treatment approach that uses a power plant’s waste heat in a forward osmosis and membrane distillation process for FGD wastewater treatment. Forward osmosis (FO) uses a working solution called a draw solution to “draw” water through the membrane which reduces the energy needed to remove FGD contaminants compared to the more traditional membrane process of reverse osmosis. In addition, compared to reverse osmosis, FO has less problematic membrane fouling and lower operational costs. Typically, FO is coupled to a secondary process, such as membrane distillation (MD), to continuously re-concentrate the working solution. MD distills water, but at lower temperatures than conventional distillation. FO and MD are particularly effective when waste heat, that is, heat that can’t be used at a plant in another way, is available for capture. In addition, Weavers’ team is developing methods to reduce membrane fouling, such as using high-power ultrasound, which produces high-energy bubbles that scour the membranes.
Limitations of the Proposed Rule
Where the pollutant limitations are more stringent, the new rule allows power plants with certain operation conditions or statuses to be regulated under more relaxed limitations using less effective treatment technologies. It also extends the implementation dates.
The newly proposed implementation timing provides an unnecessary break for the coal-fired power plants. The 2015 rule required most steam electric facilities to comply with the effluent, or waste, limitations “as soon as possible” after Nov. 1, 2018, and no later than December 31, 2023. The revision postpones the “as soon as possible” date to Nov. 1, 2020. Biological treatment is a best available technology option in both the 2015 rule and 2019 revision. Currently, at least five plants operate biological treatment systems, indicating the technology is mature and commercially available. So, postponing the implementation of the technology provides no significant benefits to power plants but delays the reduction of the amount of pollutants discharging into the receiving waters.
In addition, a subcategory for regulations created in the 2019 revision is for boilers retiring by 2028. For this subcategory, the only waste limitations set are for total suspended solids, or the particles that do not sink and must be cleaned from the wastewater. Surface impoundments such as landfills are selected as the best available technology for this type of waste. The EPA estimates that there are approximately 78 power plants or 160 generating units (approximately 22% of the 2015 Rule population) in this subcategory. This revision falls short by lacking to justifying how the year 2028 was selected. This particular subcategory creates concerns about allowing these facilities to extend the lifetime of power plants for as long as nine years with minimal or no further control for their FGD wastewater discharges.
Tarunjit Singh Butalia, research associate professor and director of the Ohio State Coal Combustion Products Program, has been investigating the stability and reclamation of coal ash impoundments for more than two decades. Research by Butalia and Chin-Min Cheng, senior research associate, has shown that the leachates from coal combustion residues contain pollutants that can potentially have negative impacts on the groundwater underlying these impoundments.
Butalia and his colleagues developed a process that uses coal combustion residues to reclaim abandoned mine lands, providing a better alternative than landfills for economical and environmentally friendly disposal of these wastes. Butalia and Cheng compare pre- and post-reclamation water quality tests to ensure that the mine reclamation using coal combustion byproducts does not worsen the water quality in the area of the reclamation.
A decision made April 12, 2019, by the U.S. Fifth Circuit Court of Appeals states that using surface impoundment as the best available technology for legacy wastewater (wastewater generated before the implementation date) in the 2015 rule was arbitrary and capricious and also unlawful under the Clean Water Act. It appears the creation of this subcategory in the 2019 EPA revision for boilers retiring by 2028 is against the court decision.
In the 2019 revision, the EPA does not change the 2015 “best available technology” regulatory options for waste streams other than waste water from flue-gas desulfurization and bottom ash transportation water. For example, in the case of combustion residual leachate, or coal ash from coal-fired power plants, the 2015 rule designated surface impoundment as the best available technology.
It is expected that the EPA will soon revisit the discharge of combustion residual leachate, because the limitations for it in the 2015 rule also were ruled unlawful in the April 12, 2019, Fifth Circuit Court decision due to their ineffectiveness on removing pollutants. The Court’s decision vacated the 2015 limitations for the leachate and remanded the issue to the EPA for reconsideration.
Compared to the 2015 rule, the EPA’s proposed revision sets up more stringent limitations for all regulated pollutants, except for arsenic and selenium. The limitations for these two constituents are relaxed, especially for selenium, which would have new limitations approximately three times higher in the 2019 revision. These limitations, set as the minimum levels of control, are based on the technology available to treat the pollutants — not by the limits that are protective of the quality of the receiving water, the water in which the facility discharges. However, plant-specific and more stringent limitations can be implemented through the Clean Water Act’s National Pollutant Discharge Elimination System that authorizes the discharges. Considering there is a safeguard mechanism provided by the Clean Water Act, the new limitations seem to provide achievable protection for the receiving water while allowing the power plants to employ the best available control and treatment technology.
U.S. EPA 2019 proposed revisions to Steam Electric Power Generating Effluent Guidelines
This blog was written by the Department of Civil, Environmental and Geodetic Engineering’s Chin-Min Cheng, senior research associate; Tarunjit Singh Butalia, research associate professor and Sustainability Institute affiliated faculty; and Linda Weavers, professor, who also is a member of the Sustainability Institute Faculty Advisory Board and co-lead of the institute’s healthy land, water and air systems research program area.