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   PID: hpt/lnx 1.9.0-cur 2019-01-08   
   TID: hpt/lnx 1.9.0-cur 2019-01-08   
    Wastewater sector emits nearly twice as much methane as previously   
   thought    
      
     Date:   
         February 28, 2023   
     Source:   
         Princeton University, Engineering School   
     Summary:   
         Researchers reveal that actual methane emissions from the wastewater   
         treatment sector in the U.S. are nearly double what existing   
         international guidelines would predict.   
      
      
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   FULL STORY   
   ==========================================================================   
   Municipal wastewater treatment plants emit nearly double the amount   
   of methane into the atmosphere than scientists previously believed,   
   according to new research from Princeton University. And since methane   
   warms the planet over 80 times more powerfully than carbon dioxide over   
   20 years, that could be a big problem.   
      
      
   ==========================================================================   
   "The waste sector is one of the largest anthropogenic sources of methane   
   in the world," said Mark Zondlo, professor of civil and environmental   
   engineering and associated faculty at the Andlinger Center for Energy and   
   the Environment. "As cities continue to urbanize and develop net-zero   
   plans, they can't ignore the liquid wastewater treatment sector."   
   Zondlo led one of two new studies on the subject, both reported in papers   
   published in Environmental Science & Technology. One study performed   
   on-the- ground methane emissions measurements at 63 wastewater treatment   
   plants in the United States; the other used machine learning methods   
   to analyze published literature data from methane monitoring studies of   
   various wastewater collection and treatment processes around the globe.   
      
   "Not many people have studied the methane emissions associated with   
   wastewater infrastructure, even though we know that it's a hotspot for   
   methane production," said Z. Jason Ren, who led the second study. Ren   
   is a professor of civil and environmental engineering and the Andlinger   
   Center for Energy and the Environment.   
      
   The Intergovernmental Panel on Climate Change (IPCC) has established   
   guidelines that allow researchers and institutions like the   
   U.S. Environmental Protection Agency (EPA) to estimate methane emissions   
   from wastewater treatment plants based on their specific treatment   
   processes. However, those guidelines were developed from limited   
   measurements at a relatively small number of wastewater treatment plants.   
      
   And when the researchers used the Princeton Atmospheric Chemistry   
   Experiment (PACE) Mobile Laboratory to quantify plant-wide emissions   
   by measuring the plumes of 63 treatment plants on the east coast   
   and in California, they found that the IPCC guidelines consistently   
   underestimated treatment plants of all sizes and treatment processes.   
      
   If the results from those 63 plants are representative, actual methane   
   emissions from wastewater treatment facilities across the U.S. would be   
   about 1.9 times greater than emissions estimates that use existing IPCC   
   and EPA guidelines, meaning that those guidelines underestimate methane   
   emissions equivalent to 5.3 million metric tons of carbon dioxide.   
      
   Interestingly, the research team who performed the second independent   
   study to analyze literature data on methane emissions came to a similar   
   conclusion: estimated methane emissions from municipal wastewater   
   treatment in the U.S.   
      
   were around double of what existing guidelines would predict.   
      
   "We were able to show, using two different approaches, that methane   
   emissions are a much bigger issue for the wastewater sector than   
   previously thought," Ren said.   
      
   The usual suspects in wastewater methane emissions The researchers believe   
   that since the IPCC guidelines were developed from limited measurements at   
   a small number of wastewater treatment plants, they might not accurately   
   represent the variation in emissions that exists between facilities.   
      
   "The guidelines assume a certain level of efficiency in these wastewater   
   treatment systems that may not exist on a plant-to-plant basis," said   
   Daniel Moore, first author of the direct measurement study and a graduate   
   student in civil and environmental engineering. He pointed to leaks and   
   inefficient equipment that may go undetected at wastewater treatment   
   plants but could lead to significant greenhouse gas emissions.   
      
   Cuihong Song, first author of the critical review and a postdoctoral   
   researcher in civil and environmental engineering at Princeton, said   
   that treatment plants equipped with anaerobic digesters were among the   
   biggest methane leakers.   
      
   Anaerobic digesters are airtight vessels containing anaerobic microbes   
   that work without oxygen to break down wastewater sludge or solid waste   
   and produce methane-rich biogas in the process. That methane can be   
   used to generate heat or electricity to power other aspects of the   
   treatment process.   
      
   But when anaerobic digesters operate inefficiently, leaks and pressure   
   buildups can allow methane to escape as fugitive emissions. "If the   
   digester is not gas- tight, you can end up with high methane emissions,"   
   Song said. The researchers found that plants with anaerobic digesters   
   emitted more than three times the methane than plants without digesters.   
      
   Higher emissions from anaerobic digesters could be a serious problem:   
   while wastewater treatment plants equipped with anaerobic digesters   
   account for less than 10% of all treatment plants in the U.S., most   
   of those plants are large facilities that, combined, treat around 55%   
   of the wastewater in the country.   
      
   "A lot of money is going into decreasing emissions by implementing these   
   digesters, because, in theory, they're closed systems. When they're   
   working correctly, you can centralize the methane into one location,"   
   Moore added.   
      
   "It's the inefficiencies and leakages that cause many of the problems."   
   Along with anaerobic digesters, the critical review found that methane   
   emissions from sewer systems contribute significantly to nationwide   
   methane emissions. However, current guidelines largely do not account   
   for fugitive methane emissions from sewers, which the researchers said   
   are important to account for in future greenhouse gas inventories.   
      
   "We have more than a million miles of sewers in the U.S., filled with   
   rich organic matter that may be causing methane emissions, but we have   
   very little understanding of their scope," Ren said.   
      
   Better monitoring, better guidelines The researchers are now working with   
   partners to build an inventory and methodology that would allow managers   
   to easily monitor their methane emissions. By identifying the sources in   
   the wastewater treatment process that release the most methane emissions,   
   their work can also inform efforts to mitigate fugitive emissions.   
      
   "Methane has a short lifetime in the atmosphere, so if we're able to cut   
   off the spout of emissions across the country, methane's contribution   
   to warming will quickly diminish," said Moore. "Ten years from now, we   
   wouldn't have to worry so much about methane."  Ren added that the methane   
   produced from processes like anaerobic digestion also serves as a valuable   
   energy source. "By identifying and mitigating fugitive methane emissions,   
   we would see double benefits," he said. "We would reduce greenhouse gas   
   emissions in the near term, and we would maximize the amount of methane we   
   can recover from the wastewater treatment process."  Still, more work is   
   needed to monitor methane emissions at various timescales from treatment   
   plants and sewer networks of different sizes and treatment processes.   
      
   For example, few studies have performed long-term, continuous monitoring   
   of methane emissions from wastewater treatment plants, even though the   
   emissions rate can vary daily or even seasonally, being generally higher   
   in the spring and summer than in the winter. "Ultimately, we need to have   
   a full accounting of the emissions from plants across many timescales,"   
   Zondlo said. He added that preliminary analyses of subsequent measurements   
   from additional plants at various times of the year have highlighted   
   the importance of understanding seasonal variation in emissions.   
      
   At the same time, researchers will need to develop better sampling   
   methods to understand emissions from hard-to-reach areas like sewers,   
   since the diffuse nature of sewer networks along with their high humidity   
   levels make it difficult to capture an accurate picture of emissions   
   with existing methodologies.   
      
   By overcoming those hurdles and continuing their monitoring efforts,   
   the researchers could contribute to a wider effort to create updated   
   guidelines that better estimate methane emissions from the wastewater   
   sector.   
      
   "Many agencies are recognizing that methane emissions from wastewater   
   sector are important to study," Ren said. "This research is not just   
   reporting our own findings. We're echoing what the broader research   
   community has observed and identified as a significant gap of knowledge."   
   Support for the research projects was provided by the Energy and   
   Environment Program at the Alfred P. Sloan Foundation (awarded alongside   
   fellow project lead Francesca Hopkins of the University of California,   
   Riverside), the High Meadow Environmental Institute via the Clear Water   
   Challenge, and the Water Research Foundation via the Paul L. Busch Award.   
      
       * RELATED_TOPICS   
             o Earth_&_Climate   
                   # Hazardous_Waste # Environmental_Policy #   
                   Recycling_and_Waste # Climate # Global_Warming #   
                   Environmental_Science # Renewable_Energy # Pollution   
       * RELATED_TERMS   
             o Methane o Automobile_emissions_control o Sewer o   
             Natural_gas o Climate_change_mitigation o Climate_model   
             o United_Nations_Framework_Convention_on_Climate_Change o   
             Greenhouse_gas   
      
   ==========================================================================   
   Story Source: Materials provided by   
   Princeton_University,_Engineering_School. Original written by Colton   
   Poore. Note: Content may be edited for style and length.   
      
      
   ==========================================================================   
   Journal References:   
      1. Daniel P. Moore, Nathan P. Li, Lars P. Wendt, Sierra R. Castan~eda,   
      Mark   
         M. Falinski, Jun-Jie Zhu, Cuihong Song, Zhiyong Jason Ren, Mark A.   
      
         Zondlo. Underestimation of Sector-Wide Methane Emissions from United   
         States Wastewater Treatment. Environmental Science & Technology,   
         2023; DOI: 10.1021/acs.est.2c05373   
      2. Cuihong Song, Jun-Jie Zhu, John L. Willis, Daniel P. Moore, Mark A.   
      
         Zondlo, Zhiyong Jason Ren. Methane Emissions from Municipal   
         Wastewater Collection and Treatment Systems. Environmental Science &   
         Technology, 2023; 57 (6): 2248 DOI: 10.1021/acs.est.2c04388   
   ==========================================================================   
      
   Link to news story:   
   https://www.sciencedaily.com/releases/2023/02/230228172159.htm   
      
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