A while ago I was writing a series of diaries on the subject of nitrogen fluxes and industrially fixed nitrogen.
I wrote several pieces for the diaries that I didn't publish here for certain reasons, but nonetheless the story itself - the issue of nitrogen and the related issue of phosphorous - remains, with or without my personal commentary, one of the least recognized and most intractable issues associated with the critical issue of energy and the environment.
Maybe you don't want to know, about it. Let's think happy thoughts.
These issues of nitrogen and phosphorous are intimately connected to another extremely important issue that is getting the minimal attention from the easily distracted public, except maybe (now) in places like Atlanta, the issue of water.
As part of the background research for the abandoned nitrogen series, I was looking at wastewater treatment strategies around the world through the prism of the published scientific literature.
Water is, of course, recycled on a grand scale. One of the biggest recycling machines for water in the world is something called "rain."
"Rain," if you must know - in spite of the representations of Ralph Nader's pal Jack T. Ripper - is in fact, not pure at all. Increasingly it is polluted with things like tetrachloroethylene (aka "dry cleaning fluid") and even, well, fluoride, and of course, nitrogen compounds.
However rain, especially with climate change, is hardly reliable any more, and in any case, it is slow - sort of like the endless hype about how solar energy will save us.
The fact is that for grand scale contaminated water - which includes the water that goes down your toilet, sinks, bathtub and other drains - a fast disposal method is needed. Historically the fast solution has been simply to dump the waste, sometimes with some treatment, but often with very little, into bodies of water. What is very interesting though is that as is often the case, some of what is dumped is actually potentially quite useful. In order to feed the earth's population - which is approaching seven billion - we are totally dependent on the two major problematic impurities found in treated or untreated sewage water.
One approach - that used for many millennia by agricultural people is to use waste effluent for agricultural purposes. This is however is not workable in modern car culture suburbs or cities - although it must be said that there are places like Southern California where, in fact, freeway landscaping, golf courses and the like are sometimes irrigated with water recovered from sewage. (Another strategy used in Los Angeles is to simply pay fines to the Federal government for dumping raw sewage into places like Bellona Creek and the Los Angeles River.)
Yet another strategy for purifying water mimics nature. This is to construct artificial wetlands, and frankly, it's a good one.
A recent paper from Norwegian scientists however, indicates that the whole wetland deal is hardly perfect, that is wholly without environmental consequence.
In the real world - and this is not widely understood in yuppie brat circles like those promoted by the highly paid (off) corporate greenwasher Amory Lovins - there is no such thing as "risk free." Despite the innumerate blabber of the set populated by the likes of Lovins, risk management is actually an exercise in combinatorial optimization.
In no place is this issue clearer than in the area of waste water treatment.
A recent paper by Norwegian scientists evaluates constructed wetlands for the treatment of waste water.
The paper is entitled "Emission of N2O and CH4 from a constructed wetland
in southeastern Norway." The reference is A.K. Søvik and B. Kløve, Science of the Total Environment 380 (2007) 28–37. The abstract is here.
Some excerpts from the article:
There is a general agreement that the observed increase in the atmospheric concentrations of greenhouse gases like carbon dioxide (CO2), nitrous oxide (N2O) and methane (CH4) has led to a warming of the earth's surface. Emission of N2O from the soil accounts for about 70% of both anthropogenic and natural sources (Smith, 1997). The concentration of N2O in the atmosphere is increasing at a rate of 0.3% per year, N2O has an atmospheric lifetime of 120 years and a global warming potential of 296 relative to CO2 (over a 100 year time horizon), and is anticipated to be responsible for about 5% of the global warming (IPCC, 2001a). Nitrous oxide also contributes to the depletion of stratospheric ozone (Mosier, 1998). Methane arises predominantly from burning of fossil fuel, ruminant animal as well as aquatic and terrestrial systems such as wetlands, flooded rice production and landfills. Methane has an atmospheric lifetime of 12–17 years, a global warming potential of about 23 relative to CO2 (100 year perspective) (IPCC, 2001b) and contributes to 25% of the global warming...
Some background:
Constructed wetlands (CWs) may be seen as combinations of natural wetlands and conventional wastewater treatment plants and are constructed in order to reduce input of nutrients to water bodies and thus prevent eutrophication. When wetlands are used for purification of wastewaters its microbial processes will likely be changed. With increased inputs of nutrients and organic matter, the productivity
of the ecosystem could increase as well as the production of gaseous compounds such as CO2, N2O and CH4. The studies conducted so far have indicated that CWs have high N2O and CH4 emissions...
The next line reminds me of the famous headline in the old (now defunct) Look magazine that remarked on the award of the Nobel Peace Prize to Linus Pauling, his second Nobel -his first was in Chemistry and he was damn close to a third Nobel Prize, in Chemistry again, except Watson and Crick stole his thunder) which read as follows:
Norway's Weird Slap at The United States
(The reason that Pauling's Peace Prize was considered a "slap" was because in the 1950's, open air nuclear weapons testing was considered "patriotic." Pauling was awarded the Peace Prize because of his work against atmospheric nuclear weapons testing.)
Here's the latest Norwegian "weird slap:"
The total area of CWs worldwide is small compared to that of all natural wetlands and agricultural areas, but the worldwide increase in the development of CWs necessitates an understanding of their potential atmospheric impact in light of the trend that natural wetlands in many countries are decreasing (e.g., USA) while environmental regulatory agencies are trying to stimulate an increase in CW acreage.
The Norwegian scientists find that most of the time their constructed wetlands emit both nitrous oxide and methane, although rarely there is a negative flux for the former. In autumn these fluxes range from -0.49 mg per square meter per day to 110 mg per square meter per day of wetland surface area. This nitrogen flux is represented by human waste, and represents the fate of the nitrogen contained in food, most of which is prepared industrially in the Haber process.
The methane situation is more or less consistently positive, with a range in autumn of -1.2 mg per square meter per day to 1900 mg (1.9 grams) per square meter per day. Impressive.
Overall though, the idea of constructed wetlands for this purpose is not necessarily a bad one, and compares favorably with simply dumping such waste directly into rivers and lakes, where the nitrogen and phosphorus will be released anyway, but causing eutrophication and similar effects like those that account for the Gulf of Mexico dead zone off the coast of Louisiana. An alternative approach - and one which may someday become necessary, should humanity survive climate change - would be to use waste water for agricultural purposes. (In this context I may at some point be inspired to write a diary on the relative merits of ozonolysis vs. chlorination.) The main risk here concerns heavy metal content. As it happens, waste water is already so used for landscape irrigation, notably in Southern California.
Anyway, I'm very fond of Norway and so I am inclined to give the last word to the Norwegians here:
When judging the effect of CWs on the global climate, it is also of importance to compare emissions from CWs to the ones from conventional wastewater treatment plants. Work on gas emissions from conventional wastewater treatment plants referred to in this study suggest that at least emissions of N2O–N may be substantially higher than the emissions from CWs (Hanaki et al., 1992; Czepiel et al., 1995). One should also have in mind that the N and C in non-treated sewage released directly into streams and rivers will be degraded elsewhere and thus still contribute to the global climate through emissions of N2O and CH4 from rivers and lakes. Finally it is also important to keep in mind that the total area of CWs worldwide is still far less than the total
area of all natural wetlands and agricultural areas.