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Clean Power Columbia University scientists find higher than expected levels of greenhouse gas emissions from wastewater treatment plants

Published on May 27th, 2010 | by Tina Casey


Greenhouse Gas Emissions from Wastewater Treatment Plants Get Closer Scrutiny

May 27th, 2010 by  

Columbia University scientists find higher than expected levels of greenhouse gas emissions from wastewater treatment plantsA team of scientists from Columbia University has found evidence that emissions of nitrous oxide from some wastewater treatment plants may be significantly higher than previous estimates.  Nitrous oxide is a powerful greenhouse gas that is almost 300 times stronger than carbon dioxide. As for the good news, the team also found indications that much of the problem could be resolved by tweaking operations at existing plants and introducing more efficient design standards in new plants, rather than developing expensive new technology.


The Columbia study provides some insight into the potential for making significant but relatively inexpensive cuts in greenhouse gas emissions by working within existing infrastructure and technology.  It  also illustrates the key role that accurate measurement plays in targeting resources to achieve the biggest bang for the greenhouse gas reduction buck.  In doing so, the study supports the logic behind the U.S. EPA’s recent proposal to expand its new greenhouse gas reporting rules.

Wastewater Treatment and Nitrous Oxide

The nitrous oxide problem is one of those “no good deed goes unpunished” conundrums.  It arises from the use by some treatment plants of a relatively new process called biological nitrogen removal, which was designed to reduce the level of ammonia in treated wastewater, rendering it less harmful to marine life when discharged into waterways.  Under ideal conditions, the process also yields nitrogen gas, which is harmless (78.8% of the Earth’s atmosphere by volume is nitrogen).  Under less than ideal conditions, the process yields nitrous oxide.

How Much Nitrous Oxide is Too Much?

The Columbia study, spearheaded by Kartik Chandran of the Fu Foundation School of Engineering and Applied Science, was a meticulous two-year effort involving a dozen wastewater treatment plants.  Until the study, it was estimated that treatment plants account for about 1.6% of total nitrous oxide emissions globally.  This was based on the assumption that nitrous oxide production only occurs in one area of the treatment process.  Chandran’s team found that emissions occur in a second area, and at even higher levels, bringing the emission factors up to two orders of magnitude higher than previously estimated.  If left unaddressed, nitrous oxide emissions are bound to grow as more treatment plants adopt biological nitrogen removal in order to meet increasingly strict water quality standards.  The alternative would be to forgo the new process and let excess ammonia continue to pollute waterways.

Cost-Effective Solutions for Greenhouse Gas Emissions

In a recent conversation with CleanTechnica, Chandran underscored the point that solutions are at hand, for existing plants as well as new ones.  For example, closer management of flow rates could enable the process to function more efficiently, lowering the production of nitrous oxide.  Another approach involves the blowers that pump air into wastewater, which enables the bacteria to function more effectively.  At some plants, blowers have been turned down in order to save energy, which can cause the treatment process to produce more nitrous oxide.  Solar energy installations at treatment plants provide a means for running blowers and other equipment at maximum effectiveness for reducing nitrous oxide emissions, without generating more carbon emissions.  Other on-site forms of renewable energy at treatment plants, such as methane gas capture and even hydrokinetic power, are also possibilities.

Update: The Columbia study was funded by the Water Environment Research Foundation.

Image: Wastewater treatment plant via eutrophication & hypoxia on flickr.com.

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About the Author

specializes in military and corporate sustainability, advanced technology, emerging materials, biofuels, and water and wastewater issues. Tina’s articles are reposted frequently on Reuters, Scientific American, and many other sites. Views expressed are her own. Follow her on Twitter @TinaMCasey and Google+.

  • rashid cheema

    Any one would like to give cheapest possible measures to protect the life of Rawal lake in Islamabad, Pakistan as it would be a dead lake after 2018.The water of this lake is largely used for drinking purpose by the inhabitants of Rawalpindi city.This is being seriously and adversely polluted due mushroom growth of residential constructions in the catchments and animal/birds sheds as well as rapid change in the environmental conditions.

    • Bob_Wallace

      Something to take a look at is a marsh treatment system.

      “The wastewater treatment plant handles all sewage for the City of Arcata. Raw sewage enters the headworks, where the sludge is separated from the effluent. The sludge is digested, dried, and composted for use on city grounds. The clarified wastewater is sent to the 49 acres of oxidation ponds where time, aquatic plants, and microorganisms purify it. Arcata’s wastewater then circulates through a six-marsh system, filled with plants and animals that feed on the nutrients that are left. The water that is finally discharged into Humboldt Bay has gone through “enhanced” secondary treatment, thanks to the marsh system, and is completely potable.”


      If done correctly it should be possible to get biogas from the initial decomposition and then fertilizer from the leftover solids. (Assuming you can keep heavy metals out of the system.)

      The marsh pond system creates an amazing wildlife area. One would never know that it was part of a municipal waste treatment system.

      The water that exits the ponds is extremely clean. It goes into Humboldt Bay and close by are major oyster farms which closely monitor the condition of the water. There has never been a water quality issue.

      Quite possibly by isolating parts of the existing lake and establishing plant growth the water in the lake could be cleaned to a much better condition than it now is in.

      If you’re interested in this idea get in touch with the people who run the web site. I think you’ll find them extremely helpful.

  • Nitrous oxide is a big deal! These systems should definitely be tweaked to avoid it. If they can capture the methane for energy that is also great.

  • Now, people are getting more and more informed of the emissions everyone of us is doing. This is a good thing for the environmentalists. At least, people are already getting to know the effects of harmful emissions in our environment.

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