Methane Releases from Septic Tanks and the Frequency of Emptying.

[NNadir]

The paper to which I'll refer in this post is this one: Challenges to Accurate Estimation of Methane Emission from Septic Tanks with Long Emptying Intervals Jakpong Moonkawin, Loi T. Huynh, Mariane Y. Schneider, Shigeo Fujii, Shinya Echigo, Lien P. H. Nguyen, Thu-Huong T. Hoang, Hai T. Huynh, and Hidenori Harada Environmental Science & Technology 2023 57 (43), 16575-16584

The paper is open to the public for free reading, but I will briefly excerpt some interesting facts in it below.

Very recently I referred in this space to the issue of the "great unmentionable," septic waste.

Changing the Language We Use About Handling, Well, to Put It Graphically, Shit: Describing Sanitation Systems.

After dangerous fossil fuel (and bioenergy) waste, aka, "air pollution and climate change," septic waste is the second largest waste releated killer on the planet, and is responsible, according to WHO, for about 1.25 million deaths per year.

WHO Sanitation.

The second most prominent greenhouse gas in the atmosphere, after CO₂ (about which humanity has chosen effectively to do nothing effective at all) is methane.

I have a septic system on my property, which a few years ago, partially owing to some activities of an unpleasant neighbor, failed, a very expensive and frankly disgusting event. I installed a very modern system utilizing an aerator to replace it.

The paper cited at the outset of this post has some interesting commentary for those of us - apparently the number is rising - who rely on septic systems to handle our household effluent.

From the text:

In 2020, the population served by on-site sanitation worldwide, including septic systems and pit latrines, exceeded for the first time than that relying on sewer connections. (1) Furthermore, since 2010, more people have reportedly been relying on septic systems than on improved latrines. (1) In Southeast Asia, septic systems are used by a majority of the population (i.e., 90% in Vietnam, (2) 84% in the Philippines, (3) and 79% in Indonesia (4)). While septic systems are preferable over open defecation, they can potentially emit substantial amounts of greenhouse gases (GHGs), such as methane (CH4). (5?8) Thus, assessing the GHG emissions from septic systems is crucial to achieving climate change mitigation. (9?11) The Intergovernmental Panel on Climate Change (IPCC) approach has been widely used to estimate CH4 emission rates (g CH4/(cap·d)) based on biochemical oxygen demand (BOD). (12) The method is based on three parameters: (i) region- or country-specific per-capita BOD (g BOD/(cap·d)), (ii) maximum CH4 production capacity (0.6 g CH4/g BOD), and (iii) CH4 correction factor or BOD removal efficiency of septic tanks (40–72%). Different from the IPCC, in Hanoi, BOD removal efficiencies of 10–50% have been reported. (13) Applying the suggested BOD removal efficiency from the IPCC might lead to a considerable estimation error in CH4 emissions from septic systems with long emptying intervals. Therefore, the goal of this article is to investigate whether the suggested BOD removal efficiency can be used to estimate the CH4 emission and, if not, what alternative indicators can be used.

A septic system is usually constructed in either of the following two ways: (i) with two components, namely, a septic tank and a soil treatment unit (e.g., leach, infiltration, or drain fields) or (ii) with only a septic tank without a soil treatment unit. The septic system of type ii has to be connected to a sewerage for further treatment. However, in low- and middle-income countries, type (ii) septic tanks are frequently found and they are not always connected to sewerage but discharged to open environments. (14,15) In this study, we focused on the septic system of type (ii) which we from here onward call septic tanks. In low- and middle-income countries in Southeast Asia, septic tanks often receive only blackwater (i.e., blackwater septic tanks), while graywater is directly discharged to a combined sewer or a drain channel... (16)

The paper offers interesting statistics and references to them:

In 2010, the wastewater sector accounted for 8% of the global anthropogenic CH4 emissions, following enteric fermentation (28%), agriculture (20%), oil and gas (18%), and landfills (10%). (48) From 1990 to 2005, global CH4 emissions from wastewater were estimated to have increased by about 35% and are predicted to increase by 28% in 2030. (49) The major contributors to emitting CH4 in the wastewater sector are the low- and middle-income countries in Asia and Africa regions, (49) where septic systems are prevalent. However, the quantification of CH4 emissions and thus the implementation of mitigation strategies within this sector pose significant challenges.

Interesting, I think.

I hope you are enjoying your Sunday.

[Chainfire]

1. Not to make light of the benefits of functioning plumbing and treatment systems.

But does feces laid under a bush create more methane than feces collected and treated in mass? I don't know.

[NNadir]

2. I really can't say, but open defecation is a serious health issue as the WHO link suggests. n/t.

[Chainfire]

4. Of course open defecation is a health hazard. I was addressing the methane issue.

I was a career master plumber, I fully recognize the benefits of sewage treatment if people are going to live in communities. I suspect, without the scientfic evidence to back it up, that far more methane is created in the bowel than in a turd and that sewage treatment systems have no effect on that.

"The plumber protects the health of the nation."

[NNadir]

6. The article suggests that farts (enteric fermentation) are indeed a serious contributor to methane.

From general reading, I think the biggest contributor may be ungulate animals, cattle being prominent.

But again, I don't have an answer to your original question, which is a good one. If I had to guess, I'd think that the presence of water favors methane formation simply because it allows the methanogenic organisms mobility, but I don't actually know the answer.

[Chainfire]

7. So, your answer begs the question, "would a system that kept poop wet longer develop more methane?"

Feces deposited in the open drys out very quickly and becomes, more or less, inert. Just curious about the process...

[NNadir]

9. On reflection, I think I can hazard an answer, albeit with limitations.

In scientific papers on water pollution, including this one, one often sees reference to BOD "biological oxygen demand." The organisms that are methanogens do not utilize oxygen for respiration, hence the produce a reduced molecule, methane, as a function of their metabolism.

Oxygen is less available in water, so I'd guess that wet sewage does produce more methane than dry feces.

Again, though, it's speculation on my part.

[Chainfire]

10. It certainly sounds reasonable.

[CrispyQ]

3. That scene from "Meet the Parents" comes to mind.

I joke, but maybe the planet wasn't meant to hold 8 billion shitting humans.
There are lots of septic tanks in the county I live in.

[Duppers]

5. "wasn't meant to hold 8 billion shitting humans."

AMEN!!!!

Sadly, there are some folks here on DU who don't understand earth's ecology. And therefore, these folks mistakenly think the planet can accommodate unlimited numbers of humans.

[Chainfire]

8. That is an unfortunate truth, but it is easier to deal with waste disposal question than lowering the population.

Of course the overpopulation problem will eventually become self correcting. It may come as a "natural" process or a process accelerated by war. We do now have the means to rapidly lower the world's population with science initially developed in the 1940s.

[hunter]

11. The world wasn't "meant to" do anything.

Like it or not, there are eight billion people living here on earth.

That's the reality we have to deal with.

Dystopian thinking, imaging a world where billions of us are suffering and dying, is hardly any more useful than imagining techno-utopias powered by magical fusion power plants and batteries.

I believe we can solve our problems with tools that already exist. We know how to limit human population growth. We know how to treat sewage. We know how to generate electricity without fossil fuels. We learned all this stuff in the twentieth century. Now we just have to do it.

[CrispyQ]

12. "Now we just have to do it."

Knowing how to do things & having the political will to do them are two different things. We've seen all over the planet what happens when a species overpopulates & yet we still did it while thinking we're smarter & better than the animals. Maybe this planet could support 8 billion people but not 8 billion people consuming because our economic systems demand that.

I believe in 20-30 years people will be stunned at the physical changes on our planet & the consequential social changes. Maybe our big brain will save us but it seems to me that pride & greed have about done this planet in. Not that Earth won't go on, it just won't be hospitable to us or all the other living things we depend on. Life is a circle, not a hierarchy, but we are still about to get slapped down a few pegs.