Wastewater GHG emissions, a poop de grace?

Section of a wastewater treatment plant.
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From the University of Cincinnati

Wastewater recycling can multiply greenhouse gas emissions

New research shows that wastewater recycling processes may generate more greenhouse gases than traditional water-treatment processes. Despite this finding, there are good reasons to continue keep wastewater recycling among the water-resource tools for urban areas.

That’s the summary of a new paper by Amy Townsend-Small, assistant professor of geology and geography at the University of Cincinnati, and a team of researchers from the University of California, Irvine. A report of their research appears in the September-October issue of the Journal of Environmental Quality.

“Advanced methods in wastewater treatment supplement fresh water supplies in areas where fresh water is scarce,” Townsend-Small said. “Climate change, caused at least in part by manmade greenhouse gas emissions, is expected to exacerbate freshwater scarcity in many of these areas, including the United States southwest.”

Townsend-Small, along with Diane E. Pataki, Linda Y. Tseng, Cheng-Yao Tsai and Diego Rosso, studied how different types of wastewater treatment affect emissions of one greenhouse gas, nitrous oxide. Nitrous oxide (N2O) is a long-lived and potent greenhouse gas, with a warming potential of about 300 times that of carbon dioxide.

“Just like carbon dioxide, nitrous oxide concentrations are increasing due to human activities,” Townsend-Small said. “Most of the increase in atmospheric nitrous oxide concentrations is due to the use of fertilizer in agriculture.”

Nitrous oxide is a by-product of the metabolism of two different types of bacteria. One bacterial type, the nitrifying bacteria, convert forms of reduced nitrogen (like ammonium) to oxidized forms of nitrogen (like nitrates). Another type of bacteria, the denitrifying microbes, convert nitrates into inert nitrogen gas.

“The same microbes that live in agricultural soils also thrive in wastewater treatment and water recycling plants,” Townsend-Small said. “The same nitrification and denitrification processes are employed in these plants to remove nitrogen from wastewater.”

Townsend-Small and her colleagues compared the nitrous oxide emission rates at two different types of wastewater treatment plants in southern California. The first type was a conventional wastewater treatment plant, where the objective is to remove organic carbon and return the treated wastewater to a river or the ocean. The second type was a wastewater recycling plant, where both organic carbon and nitrogen are removed, and the treated wastewater is used for irrigation of landscaping and urban greenspace.

“Wastewater reuse for irrigation, otherwise known as ‘showers to flowers’, potentially reduces overall freshwater consumption in southern California, which is threatened by dwindling supply and a growing population,” Townsend-Small said.

However, she and her co-authors found that the wastewater recycling plant emitted about three times more nitrous oxide than the traditional treatment, when all factors are included. The researchers’ data indicate that dense populations of nitrifying and denitrifying bacteria in the wastewater recycling plant were the cause of these high nitrous oxide emissions. They also did preliminary calculations on the impact of wastewater recycling plants on nitrous oxide emissions in southern California.

“Because the Los Angeles area is so heavily urbanized, our calculations indicate that nitrous oxide emissions from wastewater treatment and recycling are several orders of magnitude larger than agricultural nitrous oxide emissions in the region,” Townsend-Small said.

Despite the production of nitrous oxide, the authors conclude that – taken in context – wastewater recycling is still a good idea.

“Wastewater recycling is an essential component of the urban water-resource portfolio, especially in the semi-arid, urban southwest,” Townsend-Small said. “Because drinking water in southern California is imported over very long distances, it is responsible for large energy consumption and carbon-dioxide emission rates.”

Southern California’s thirst also affects the areas from which it draws its drinking water, mostly Arizona and northern California, and disrupts aquatic habitats. The authors propose that cities allow recycled wastewater to supplement drinking water supplies, not just irrigation water.

“If wastewater recycling can supplement drinking water resources and not just irrigation water for landscaping, then overall greenhouse gas emissions could be reduced, as could the potential for water scarcity in southern California and beyond.” Townsend-Small said.



The research was supported by funding from the National Research Initiative of the US Department of Agriculture and the Urban Water Research Center at the University of California, Irvine.

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August 29, 2011 1:56 pm

If wastewater recycling can supplement drinking water resources and not just irrigation water for landscaping..
Sure, just as soon as the EPA can set rules around it. To date, they have not. For example, Denver Water advertises the waste water it treats and releases back in to the river system is cleaner than the water it pulls out. However, because EPA has not set rules and guidelines around re-using treated water, the treated water can only be use for irrigation. The treated water it releases back into rivers/streams is re-treated downstream, resulting in duplication of treatment…

August 29, 2011 2:16 pm

Oh noes! It’s the N2O’s!
So …. how many parts per trillion of the atmosfear (sic) is N2O, then?

August 29, 2011 2:46 pm

Of NOx use of water to be sure.

Andrew Parker
August 29, 2011 2:58 pm

The EPA is not the only obstacle to the reuse of treated effluent. Water Rights laws are very restrictive here in the Western US. Traditionally, the right to water is for single use. Anything left over goes downstream to the next user.
Similar restrictions also apply to use of rainwater or snowmelt from your property. You must own a separate right to impound water that falls on your property, otherwise, it belongs to the next rightful user, downstream. Some states have recently passed laws that allow a small amount of water to be stored for yard irrigation.
There have been some plans here in Utah to use treated effluent for yard irrigation. I do not know if any of them have overcome the regulatory hurdles.

August 29, 2011 3:04 pm

There’s another issue of quality control. If a process upset results in the spread of e coli, six sigma isn’t good enough.

August 29, 2011 3:08 pm

You add nitrates and other nitrogen compounds to fields as fertilizers so why would you want to remove it from water intended for irrigation? I maybe could see if they were planning on drinking it depending on the concentration but removing from water intended for irrigation seems insane.

Sam Hall
August 29, 2011 3:27 pm

“The same nitrification and denitrification processes are employed in these plants to remove nitrogen from wastewater.”
OK, so you release nitrogen. Just what is the problem with that?

Jim Verhei
August 29, 2011 4:19 pm

OK. But how are flushed medications taken care of … will my deep baritone voice take on a soprano tinge ?

August 29, 2011 4:44 pm

This is a bizarre report. Why on earth would one consider the greenhouse imposte of wastewater recycling to be more important than the ecological impacts of continuing to use dwindling freshwater resources. Nice to know, but only a sidenote. Probably did the research this way cos you cant get a grant to do normal science any more.

August 29, 2011 9:11 pm

In Canada, indoctrination runs high in British Columbia where the green lobby is brainwashing public employees:

CRS, Dr.P.H.
August 29, 2011 9:56 pm

Sam Hall says:
August 29, 2011 at 3:27 pm
“The same nitrification and denitrification processes are employed in these plants to remove nitrogen from wastewater.”
OK, so you release nitrogen. Just what is the problem with that?
CRS Reply It’s called “eutrophication,” wherein the excess nutrient load in the wastewater discharge stimulates the growth of undesirable algae in receiving waters. USEPA has gone after phosphorus in a big way, so now they are setting their sights on nitrogen.
Quite honestly, if you throw the air pollution treatment dollars somewhere, they should be thrown at the plants that produce nitric and adipic acids. This is a very easy fix, there aren’t than many plants, and the relative impact would be huge. Chasing around emissions from farmland, rice paddies, manure etc. is a fool’s errand.

August 29, 2011 10:46 pm

There is water recycling for domestic consumption going on now in Orange County, OCWD. It’s called “Toilet to Tap”.
These days, you’ll find regulatory agencies are more frequently making it prohibitive to discharge wastewater into streams. NPDES permits get more restrictive. The idea is to stop discharging all pollutants. So will we have to make distilled water anyway?
And don’t count on keeping your water rights. The definition of “Waters of the United States” is changing rapidly.
Medications are going to be at parts per trillion levels, and not a concern. However, they will very likely end up on the list of compounds that must be measured and reported – at significant cost.
A very big problem with reusing water that is not treated to tertiary standards and / or not properly filtered and disinfected to supplement household irrigation is the potentail for cross-contamination of the drinking water supply. It is not a trivial issue. Backflow prevention will be needed on every domestic connection that has a raw water or reused water supply. Just running the pipes in the streets is not simple either. There are regulations to prevent leakage of contaminated water from entering the distribution system. The costs for installation, operation and maintenance of a third water delivery system in addition to distribution and collection is difficult to justify, except perhaps where water is in very short supply. The simplest solution is to stop putting in tropical lawns and gardens in desert climates. Native plants can be quite appealing.
We need to develop RO technology and supply inexpensive abundant energy to drive it (we can do that). California has the Pacific Ocean that could serve as an unlimited supply of water for the coast. That would leave the water falling on the Sierra Nevada for the local residents and biota. When the state reaches 50+ million population, moving water hundreds of miles won’t be the answer anyway. Green energy will never supply the energy we need to make the water we need or pump it uphill from the ocean.
The Delta controversy is another government power grab justified by very poor science. The new Commission is planning to take control of water in Northern California, and levy huge new fees on water used as a fund to support their schemes. They try to claim that areas of origin, i.e. the watersheds, are beneficiaries of the Delta (way downstream). The real beneficiaries, the people getting Northern California water, are the ones who should be paying to support the watersheds and paying the costs of maintaining the Delta.
The real answer for the Delta is to recognize it is a poor delivery system for ag water and raw water for Southern California domestic users. There should be a separate conveyance constructed. Using an estuary in an attempt to transport fresh water is not a particularly sensible approach.

Steve C
August 30, 2011 12:17 am

Recent history should tell you what to expect. Before long, waste water will be declared a “pollutant”, like CO2, and they’ll start taxing hell out of anyone who produces any. And thus is taken another step back towards the Dark Ages, when one might take a bath “once a year, whether one needs it or not”.

August 30, 2011 12:25 am

you want to remove it from water intended for irrigation?

Allan M
August 30, 2011 12:42 am

The tap water where I live comes from the longest ‘river in li’l old England.’ We know it’s good certified quality because it’s been ‘passed’ by every local council upstream.

August 30, 2011 1:10 am

so decomposition increases CO2. Is that why the areas around the globe with the greatest CO2 emissions, as seen by satellite, are the African, South East Asian and South American rain forests?

August 30, 2011 2:02 am

This stuff drives me crazy ! Some factoids:
– Nitrous oxide (N2O) comprises 0.3 ppmv (0.00003%) of the atmosphere. Egads !
– Nobody knows the actual residence time of atmospheric N20
– The N2O emissions from sewage treatment plant is likely pretty small in global significance since relatively large amounts are thought to be emitted from soils and ocean waters by comparison.(but these processes and their magnitude are poorly known).
– There is no indication that the N2O NOT emitted from “normal sewage treatment” would NOT eventually be emitted from effluent downstream bacteriological processes. The ‘undigested’ nitrogen products remaining in the effluent remain bacterial substrates which could produced N2O.
In conclusion, sewage treatment plants are not the only places processing crap.

Alan the Brit
August 30, 2011 2:04 am

I agree with Jerome, just how many ppb are actually in the atmosphere. There is so little technically speaking it may as well not exist!
AND as already noted above, London’s water supply has been used & treated multiple times before a Londoner drinks any!!!! They seemed fairly reasonable types when I was last visiting there, one head, two ears, two eyes, & one mouth, thankfully used in that order for the most part! People seem to forget that illness & disease are prevented by water treatement after extraction, for consumption, whereas before it was rife. A whole bunch of critters seemed to enjoy relieving themselves in it I have observed in the past, not a pleasant thought at all!

John Marshall
August 30, 2011 2:16 am

At least one molecule of water in a glass full has been passed by Julius Cesear. There is no new water on this planet, well hardly any apart from the little that occasionally falls from space.

August 30, 2011 3:00 am

Sounds like bioenginering has a ways to go before it’s “settled” (if you know what I mean). Sounds like something is missing in the wastewater world that eliminates this little problem. Oh Culligan Man! Oh Culligan Man!
PS: Wastewaterology must not be as old as Climatology where ‘Everything is Settled”.

Alan Watt
August 30, 2011 11:18 am

Oh the irony! Nitrous Oxide (N20) is laughing gas.
We’re worried too much free Nitrous Oxide will do what — give everyone a good laugh?
Was this study released in April perhaps?

Jim G
August 30, 2011 12:33 pm

Poop de grace? Great treminology. I love it! If we freeze to death or drown in our own excrement it will probably be because we run out of useable, reliable energy due to ignorant government policies.

Allan M
August 30, 2011 12:52 pm

Alan the Brit says:
August 30, 2011 at 2:04 am
AND as already noted above, London’s water supply has been used & treated multiple times before a Londoner drinks any!!!!
Earlier comment: The tap water where I live comes from the longest ‘river in li’l old England.’ We know it’s good certified quality because it’s been ‘passed’ by every local council upstream.
The river Thames is only the 2nd longest river in England (215mi). I live near the Severn (220mi.)
So there!

CRS, Dr.P.H.
August 30, 2011 6:45 pm

Interesting that this article was just posted:

But as Nemeroff points out, there is a certain irony to this position, at least when viewed from the perspective of a water engineer. You see, we are all already basically drinking water that has at one point been sewage. After all, “we are all downstream from someone else,” as Nemeroff says. “And even the nice fresh pure spring water? Birds and fish poop in it. So there is no water that has not been pooped in somewhere.”

Make beer out of it, I says!

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