February 2012, Vol. 24, No.2
Study finds health of Chesapeake Bay may be improving
Researchers have identified a positive trend in the health of Chesapeake Bay. A study analyzing 60 years of water quality data from the bay has found that the size of mid- to late-summer oxygen-deprived zones, known as “dead zones,” have been declining since the late 1980s, according to a University of Maryland (UMD; College Park) news release. This timing coincides with the effort to cut nutrient pollution through the multistate and federal Chesapeake Bay Program.
Looking at dead zones in deep channels of the bay, researchers from Johns Hopkins University (Baltimore) and the UMD Center for Environmental Science also discovered that the duration of these zones is linked closely to the amount of nutrients entering the bay.
“This study shows that our regional efforts to limit nutrient pollution may be producing results,” said Don Boesch, president of the center. “Continuing nutrient reduction remains critically important for achieving bay restoration goals.”
In recent years, the bay has been experiencing an early-summer spike in dead zones, and researchers have speculated that decreasing the amount of nutrients entering the bay has not been improving its health, the news release says. But this study found that the early-summer increases are influenced by climate elements, such as wind, sea level, and salinity of the water — not by runoff nutrient pollution, the release says.
“We believe … that without those efforts to rein in the pollutants, the dead zone conditions in June and early July would have been even worse,” said William P. Ball, study co-author and professor of environmental engineering in the Whiting School of Engineering at Johns Hopkins.
The study, which was supported by funding from the U.S. National Science Foundation, U.S. Department of Commerce, and U.S. National Oceanic and Atmospheric Administration, was published in the November 2011 issue of Estuaries and Coasts. It is part of a larger 5-year Chesapeake Bay Environmental Observatory project, which is funded through the Chesapeake Research Consortium (Edgewater, Md.).
Reclaiming wastewater can increase nitrous oxide emissions
Wastewater reclamation processes have been found to generate more nitrous oxide than traditional wastewater treatment processes, according to a recent research report.
Nitrous oxide, a greenhouse gas, is a byproduct of the metabolism of two different types of bacteria. It often makes its way into the atmosphere from fertilizer use, according to Amy Townsend-Small, lead author of the report and assistant professor of geology and geography at the University of Cincinnati. The gas also can come from wastewater treatment, since the same microbes that are responsible for emitting the gas in agricultural soils also thrive at wastewater treatment plants, according to an article in UC magazine.
The researchers compared emission rates of a conventional wastewater treatment plant, where the objective is to remove organic carbon and return the treated wastewater to the environment, to a wastewater recycling plant, where both organic carbon and nitrogen are removed and treated wastewater is used for irrigation, the article says. The recycling plant emitted about three times more nitrous oxide than the traditional treatment plant. The research indicates that dense populations of nitrifying and denitrifying bacteria in the recycling plant caused these high emissions, the article says.
But the researchers emphasize that wastewater reclamation is still necessary, calling it “an essential component of the urban water resource portfolio, especially in the semiarid, urban Southwest,” according to Townsend-Small. She said that this is especially important because drinking water in Southern California is imported from distant locations, adding to energy consumption and carbon dioxide emission associated with potable water.
The research report’s authors propose that cities allow reclaimed wastewater to supplement drinking water supplies in addition to irrigation water, because then the “overall greenhouse gas emissions could be reduced, as could the potential for water scarcity in Southern California and beyond,” Townsend-Small said.
Funding from the National Research Initiative of the U.S. Department of Agriculture and the Urban Water Research Center at the University of California–Irvine supported the research. The research report, written by Townsend-Small and a team of researchers from the University of California–Irvine, was published in the September–October issue of the Journal of Environmental Quality.
New model quantifies nitrous oxide emissions
Researchers have developed a model to quantify nitrous oxide emissions from activated sludge plants and demonstrate how this could be used to evaluate the effects of process configuration and loading patterns. The December issue of Water Environment Research (WER) contains an article on this work.
Nitrous oxide emissions from wastewater treatment plants are variable and difficult to measure, and results often are not accurate, the article says. Emissions have a strong correlation to nitrification, which results in elevated nitrite concentrations. The article attempts to help predict conditions where greater emissions might be expected. The authors note that a model-based approach to estimating nitrous oxide emissions would be an improvement over the current approach of using static emission factors that do not account for such factors as process configuration, dynamic loading patterns, and environmental conditions.
The model describes the link between the presence of ammonia and nitrate accumulation and the increase in emissions. The authors also found that low dissolved-oxygen concentrations may be implicated through differential impacts on ammonia-oxidizing bacteria versus nitrite-oxidizing bacteria activity. The model was applied to data from laboratory and pilot-scale systems to determine that plant configuration, influent loading patterns, and certain operating strategies all are important factors in determining nitrous oxide emissions.
The authors expect continuous refining and calibrating of the correlation function will occur as more data become available and the understanding of nitrous oxide generation from nitrification grows, the article says. The article, “N2O Emissions: Modeling the Effects of Process Configuration and Diurnal Loading Patterns,” appears in the December issue of WER and can be downloaded free at bit.ly/xLWs5a.
Water Environment Research allows open access to one article per issue on a range of important technical issues such as nutrient removal, stormwater, and biosolids recycling. Find more open-access articles at www.ingentaconnect.com/content/wef/wer.
In the December issue, the Operations Challenge section misidentified the team members of the Regulators from the Ohio Water Environment Association. They are employees of the Ohio Environmental Protection Agency (EPA), not the U.S. EPA. The story also misspelled the surname of the Regulators team captain. He is Walter Ariss, not Arsis.
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