Clean Coal Wastewater Treatment
Clean coal wastewater treatment is a unique concept that (1) mitigates the harmful atmospheric emissions associated with coal combustion and (2) eliminates the pollution of waterways caused by wastewater treatment plant effluent discharges. In addition to its pollution control features, the technology yields pipeline-quality natural gas and algae-based products, such as animal feed, fertilizer and biofuel feedstock.
Clean coal wastewater treatment begins with the “hydromethanation” process. The inputs for the hydromethanation process are a carbon source (such as coal or biomass) and water. The process converts the carbon source into pipeline-quality natural gas (methane) and carbon dioxide in equal proportions. The hydromethanation process results in the systematic removal of both heavy metals and gaseous pollutants from the product methane for recycling. Carbon dioxide is also separated in the process by means of a gas separation unit. See, www.greatpointenergy.com/ourtechnology.php. Treated wastewater is a cost-free water source for the co-located hydromethanation facility.
Wastewater enters the treatment plant’s primary clarifiers where sludge settles and is collected. The sludge is delivered to an anaerobic digester, which yields a biogas comprised of methane and carbon dioxide. The wastewater discharged from the clarifiers, including suspended solids and high-nutrient liquid, is then released to an algae pond for secondary treatment. The carbon dioxide stream from the hydromethanation gas separation unit is recycled into the algae pond, which enhances algae growth during the secondary treatment process. See, www.nrel.gov/biomass/pdfs/lundquist.pdf. Waste heat from the hydromethanation process can be used to maintain normal temperature ranges in the anaerobic digester and the algae pond even in northern climates. The algae remove carbon dioxide, nitrogen and phosphorus from the wastewater. The algae are then harvested. See, http://www.hydromentia.com/Products-Services/Algal-Turf-Scrubber/Product-Documentation/ATS-FAQ.html. The harvested algae are useful as an animal feed, fertilizer or as a biofuel source. All of the treated effluent from the algae ponds is diverted to the hydromethanation unit. There is no effluent discharge into a receiving stream, which is a unique feature of this technology.
Clean coal wastewater treatment technology allows the use of domestic coal resources in an environmentally responsible manner while also addressing incipient water pollution issues. Harmful atmospheric pollutants, typically associated with coal combustion, are captured during the hydromethanation process. Sludge and coal are converted into clean-burning natural gas. Carbon dioxide is recycled to enhance algae growth. No wastewater effluent is discharged from the treatment plant and the deleterious environmental effects, associated with even treated wastewater discharges, are eliminated.
Finally, it should be noted that energy expenses are normally 30% of the operation and maintenance costs of a wastewater treatment plant. Wastewater treatment plants account for about 3% of the electric load in the United States and that demand is only expected to grow in the future. See, www.p2pays.org/energy/WastePlant.pdf. Because of the relatively passive nature of this wastewater treatment technology, there will be major energy cost savings for treatment plant operators, which will serve as a powerful economic incentive to convert wastewater treatment plants to clean coal wastewater treatment facilities.
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