April 2012, Vol. 24, No.4
Human sourced nitrogen has made its way into lakes for more than a century
Nitrogen from human activities has been polluting lakes throughout the Northern Hemisphere for more than a century, even in remote lakes located thousands of miles away from the nearest city, industrial area, or farm, according to research published in the journal Science.
Research based on historical changes in the chemical composition of bottom deposits in 36 lakes from the U.S. Rocky Mountains to northern Europe showed that more than 75% of the lakes studied had a distinct signal of nitrogen released from human activities before the start of the 20th century, according to a University of Washington (Seattle) news release. This long-term nitrogen pollution was identified in 25 remote lakes in the Northern Hemisphere, ranging from temperate and alpine to arctic areas, the news release says.
“Our study is the first large-scale synthesis to demonstrate that biologically active nitrogen associated with human society is being transported in the atmosphere to the most remote ecosystems on the planet,” said the study report’s lead author Gordon Holtgrieve, a researcher at the University of Washington School of Aquatic and Fishery Sciences.
Because of the broad geographic and ecosystem-type distribution, researchers believe the nitrogen comes from atmospheric deposition, Holtgrieve said, according to the release. Humans contribute to nitrogen in the atmosphere by such activities as burning fossil fuel and using fertilizers. Atmospheric nitrogen then is distributed through air currents back to Earth in rain and snow, the release says.
Researchers used statistical models to analyze nitrogen characteristics of lake sediments and determined that nitrogen pollution started approximately 115 years ago, shortly after the Industrial Revolution, the release says. Researchers also found that the rate of chemical changes increased during the last 60 years with industrial production of nitrogen for fertilizers. The estimated increase in fertilizer use will result in an increase in this presence, said report co-author Peter Leavitt, a professor of biology and holder of the Canada Research Chair in Environmental Change at the University of Regina (Saskatchewan), in the news release.
The effect of nitrogen on remote land and lakes is largely unknown but could alter the biological composition of microscopic communities, as seen in Arctic lakes with the arrival of human-derived nitrogen, the release says.
The study was funded by the Gordon and Betty Moore Foundation (Palo Alto, Calif.), U.S. Fish and Wildlife Service, Alberta Water Research Institute (Edmonton), Natural Sciences and Engineering Research Council of Canada, U.S. National Science Foundation, and Canada Foundation for Innovation.
Antibiotic-resistant bacteria levels higher near effluent discharge sites
AUniversity of Minnesota (Minneapolis) study has found that releasing treated municipal wastewater can increase the number of antibiotic-resistant bacteria, called “superbacteria,” in surface water. Wastewater treated using standard technologies likely contains larger quantities of antibiotic-resistant genes in bacteria that can go unnoticed because of background levels of bacteria in surface water, according to a University of Minnesota news release.
Superbacteria develop in people taking antibiotics, are shed during defecation, and travel to municipal wastewater treatment facilities. Researchers examined surface water samples taken from near an effluent outfall and compared them to other nearby surface water samples.
The Duluth, Minn.-area wastewater treatment facility that provided the effluent-containing samples uses primary and secondary treatment, as well as tertiary treatment — a mixed media filter — to remove additional bacteria and nutrients, the news release says. Researchers also examined surface water samples from 13 locations in the St. Louis River, Duluth–Superior Harbor, and Lake Superior in northeastern Minnesota.
The comparison of the highly treated effluent and the area’s pristine surface waters, which have low background levels of bacteria, helped researchers determine that levels of antibiotic-resistant genes and human-specific bacteria were much higher in the effluent-containing sample. For instance, superbacteria concentrations were up to 20 times higher where effluent was released into the Duluth–Superior Harbor, compared to the other surface water sample sites, the release says. However, overall bacteria levels were still relatively low in surface water samples, the release says.
“Current wastewater treatment removes a very large fraction of the antibiotic resistance genes,” said Timothy LaPara, lead author of a recent research report on the study and a University of Minnesota civil engineering associate professor, in the news release. “But this study shows that wastewater treatment operations need to be carefully considered and more fully studied as an important factor in the global ecology of antibiotic resistance.”
The research was funded by the U.S. National Science Foundation. The research report, “Tertiary-Treated Municipal Wastewater Is a Significant Point Source of Antibiotic Resistance Genes Into Duluth–Superior Harbor,” appeared in the journal Environmental Science and Technology and was part of a graduate-level civil engineering class project at the university.
Advanced controls decrease energy, increase nitrogen removal
Researchers have evaluated aeration control technologies to determine the best control concepts for specific conditions. An article appearing in the February issue of Water Environment Research (WER) details this work.
Aeration consumes about 60% of the total energy used by wastewater treatment plants, but advanced process controls can reduce energy consumption and carbon footprints, while improving effluent quality. But, data quality and signal availability can limit success, the article says.
Researchers conducted extensive measurements, simulation studies, and full-scale implementation of aeration control at three conventional activated sludge plants with fixed pre-denitrification and nitrification reactor zones. According to the article, “full-scale energy savings in the range of 16–20% could be achieved together with an increase of total nitrogen removal of 40%.”
Additional capacity recovered by optimizing nitrification process can be used to introduce anoxic or anaerobic phase, both of which enable better biological nitrogen and phosphorus removal. These gains also lead to lower chemical doses and less solids production.
“The primary goal of this project was to demonstrate that increasing nitrogen removal in parallel with a reduction of the energy consumption is viable using control technology,” the article says.
The article, “Improving Nutrient Removal While Reducing Energy Use at Three Swiss WWTPs Using Advanced Control,” appears in the February issue of WER and can be downloaded free at www.ingentaconnect.com/content/wef/wer.
The February article “Patenting a new identity” incorrectly stated that Ostara Nutrient Technology Inc. (Vancouver, British Columbia) invented the Pearl® Process. In fact, the technology was invented by a team of researchers from the University of British Columbia, patented by the university, and licensed to Ostara, who named the process.
The February article “Disinfection options for reuse,” stated pasteurization temperature and time requirements that read, “higher than 82°C (180°F) and maintained for 10 minutes.” The time requirement should be 10 seconds.
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