January 2012, Vol. 24, No.1
Conventional wastewater treatment ineffective at degrading sucralose
Following the trail of the popular artificial sweetener sucralose after digestion in the human body, researchers have determined it resists breakdown during conventional wastewater treatment and makes its way into surface water and groundwater.
“Essentially all of the sucralose consumed in foods ultimately winds up in wastewater treatment plants,” an Arizona State University (Phoenix) news release says.
Research led by César Torres, and Rosa Krajmalnik-Brown at the university’s Biodesign Institute looked at how well chemical disinfection and anaerobic or aerobic degradation remove the highly soluble chlorinated carbohydrate from wastewater, according to the news release.
To test the biological degradability of the sweetener, researchers collected wastewater samples at seven full-scale wastewater treatment plants in southern Arizona. They examined lab-scale anaerobic and aerobic biodegradation of sucralose in biological batch reactors, which ran for at least 48 days, the news release says. The researchers examined three experimental conditions using sucrose, sucralose, and a combination of the two in the batch reactors.
For each of the seven plants and in all three experimental conditions, researchers found no significant sucralose degradation, indicating that sucralose is highly resistant to all forms of treatment, the news release says.
On the chemical degradation side, researchers examined the effects of disinfection with chlorine, ozone, or ultraviolet light. In all three cases, sucralose degradation was found to be negligible. However, the researchers noted, resistance of sucralose to degradation may have a positive side: Because the sweetener does not break down at all, it does not form intermediary chlorinated products that are highly toxic to humans.
The study showed that additional steps beyond conventional treatment techniques are required to degrade or remove sucralose from wastewater. One possibility is filtration through activated carbon, which has been shown in other studies to enhance sucralose removal.
Laundry may be cause of microplastics in the ocean
Microplastics — portions of polyester, acrylic, and other synthetic polymers smaller than 1 mm — enter the environment from washing-machine wastewater, according to a study led by Mark Anthony Browne of the University College Dublin (UCD; Ireland) School of Biology and Environmental Science. The study was featured in a journal article, “Accumulation of microplastic on shorelines worldwide: Sources and sinks,” which was published online Sept. 6 in Environmental Science and Technology.
Researchers found that more than 1900 fibers can be shed from a single piece of clothing during a single washing-machine cycle, according to a UCD news release. The research provides insights into the sources, sinks, and pathway of microplastic into habitats and shows that 18 shores across six continents were contaminated with microplastic, the release says.
Browne and his team used forensic techniques to examine a marine disposal site for wastewater solids and effluent from wastewater treatment plants to identify the main source of microplastic contamination on beaches. After evaluating microplastic from sediments, researchers found that the proportions of polyester and acrylic fibers used in clothing resembled those found in habitats that receive wastewater discharges and in the wastewater itself, according to the article abstract. The researchers then studied domestic washing machines and determined that washing synthetic clothing and blankets releases more than 100 fibers per liter of effluent, the news release says. This suggests that washing clothes is likely to be a major source of microplastic fibers on coasts worldwide, rather than fragmentation of plastic waste or cleaning products.
The research team, which also included scientists from the University of Sydney (New South Wales, Australia), University of Plymouth (England), and University of Exeter (England), concluded that more work is needed to determine if microplastic can transfer from the environment and accumulate in food webs through ingestion, the news release says. Humans can inhale microplastic fibers into lung tissues, and the fibers can be associated with tumors. Research also is needed to develop methods for removing microplastic from wastewater and determine which fibers pose less of a problem for habitats, animals, and humans, Browne said.
“It’s difficult to find funding for this necessary research, and we are hoping that industry and government soon recognize its importance and provide more,” Browne said.
The research was funded by Leverhulme Trust (London), the Centre for Research on the Ecological Impacts of Coastal Cities at the University of Sydney, and Hornsby Shire Council (Sydney).
November WER examines the treatability of petroleum refinery waste
In the November 2011 issue of Water Environment Research (WER), researchers evaluate the ability of the activated sludge process to treat a segregated stripped sour-water stream from a petroleum refinery.
Petroleum refinery stripped sour water is a high-strength wastestream that can represent a significant fraction of the chemical oxygen demand and ammonia in refinery wastewater. Typically, the wastestream is blended with other process wastewater before biological treatment, but this study was performed to determine if it could be treated biologically before blending with other wastewater, the article says.
For the study, a pilot activated sludge plant was operated to promote nitrification to determine if the system would nitrify. The plant was operated in two periods. One was terminated after 19 days because of excessive sludge bulking. The second operated for 70 days, and sludge bulking was eliminated by operational changes, which included aerating the influent to oxidize reduced sulfur, adjusting the influent acidity, and adding micronutrients to satisfy biological requirements. The pilot plant provided a chemical oxygen demand removal of up to 93%, and nitrification was achieved, the article says.
“These results indicate that direct treatment of [stripped sour water] with activated sludge process is possible and has direct application to full-scale petroleum refinery,” the article says.
The article, “Petroleum refinery stripped sour water treatment using the activated sludge process,” is available as an open-access document and can be downloaded free at http://goo.gl/N3NCu.
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.
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