So many possible headlines, but how about 'The Other Black Gold'
May 27, 2022 10:50 PM   Subscribe

 
Great article.
posted by Keith Talent at 11:48 PM on May 27


Mmmm "sewage smoothie"
posted by chavenet at 1:03 AM on May 28


Here in austin, they sell something called "Dillo Dirt" at every hardware store, that my understand is soil made from compost and material reclaimed from the sewage system.
posted by RustyBrooks at 3:45 AM on May 28


I believe Milorganite is the same idea.
posted by Insert Clever Name Here at 4:59 AM on May 28 [1 favorite]


All well and good in the past. One minor glitch with this is that most cities outflow is so polluted with pharmaceuticals, recreational drugs, and chemicals from processed foods that it would be positively unsuitable to utilize the material. The cost of processing this to make it 'safe' would far exceed the benefit. Far better to use it as bio-fuel and use the energy created from that.
posted by IndelibleUnderpants at 6:11 AM on May 28 [9 favorites]


Now imagine the mind-boggling piles of excrement that the planet’s 7 billion people generate in just 24 hours. Multiply it by 365 days a year, and it will likely make you gasp: Holy crap!
Like much urban activity, this mind boggling number pales into insignificance compared to the quantities of similar substances involved in agriculture. Collectively we manufacture many times more pig, chicken and cow shit than human shit, and much of that is routinely wasted as pollution as well.

Also worth noting that the most potent fertilizer produced by human beings isn't our shit but our urine. Any process involving flush toilets obviously makes that distinction moot, but it does mean that your compost heap is a much more ecologically sound thing to piss into than your toilet.

Urine is also a much less likely disease vector than faeces because nowhere near as many pathogens find bladders as hospitable as colons; I have no problem whatsoever with eating tomatoes that have spent their whole growing season being fertigated by somebody who takes a whizz in their watering can before filling it up.

I'll also be the one who inserts the obligatory link to The Humanure Handbook into this discussion.
posted by flabdablet at 6:29 AM on May 28 [12 favorites]


Visceral disgust, hey?

I'm curious about the drugs aspect too. The article doesn't mention it.
Our estuary is polluted with raw sewage, and one of the results is finding ibuprofen in the fish.
Still, my little bit of googling suggests that sewage processing does deal with this to some extent?
posted by Zumbador at 6:33 AM on May 28


Zumbador at 6:33 AM on May 28

Sadly, there is still significant residue that passes through all forms of (cost effective) treatments. This from Pfizer "Typically, a fraction of the medicines taken by patients is naturally excreted and may enter waterways following treatment by a municipal wastewater treatment plant.". And there are other comments made by Big Pharma as part of the 'cover our asses' needed to appear environmentally responsible.

Equally, look at a processed food packet and see how many added chemicals there are. Not being hippy dippy here just pragmatic. As mentioned above, the article fails to address the 'chemical residue' issue. We grow a lot of our own food but there is NO WAY I would even consider putting my own or others poop on there. We have chickens and the residue from them goes on separate piles that allow it to digest and compost over several years before we even consider putting it on the beds.
posted by IndelibleUnderpants at 6:41 AM on May 28 [4 favorites]


One minor glitch with this is that most cities outflow is so polluted with pharmaceuticals, recreational drugs, and chemicals from processed foods that it would be positively unsuitable to utilize the material.

The outflow, at least in part, from my cities system is used to irrigate and fertilize a golf course.
posted by Mitheral at 6:43 AM on May 28


One minor glitch with this is that most cities outflow is so polluted with pharmaceuticals, recreational drugs, and chemicals from processed foods that it would be positively unsuitable to utilize the material.

Can you provide any citations that back this up?
posted by zamboni at 7:40 AM on May 28


Pharmaceutical residues in wastewater are a well known concern.

“Chemicals from processed foods” feels like stretching it - they were allowed in food the first time around! - but my link does note artificial sweeteners as being found in wastewater as well.
posted by atoxyl at 7:51 AM on May 28 [2 favorites]


This is a great article, but really I feel like the entire thing was a lead up to the amazing pun in the last sentence.
posted by destrius at 8:10 AM on May 28


Melbourne, Australia, is a city of about five million people. Here's where its sewage goes.

Sydney, Australia, has about the same population. Most of its sewage is still dumped into the sea after only primary treatment, though further out than it used to be.
posted by flabdablet at 8:18 AM on May 28 [1 favorite]


my link does note artificial sweeteners as being found in wastewater as well

One of those is sucralose, a chlorinated carbohydrate that remains mostly unmodified on its way through the human body and probably breaks down more readily in compost than in wastewater.
posted by flabdablet at 8:41 AM on May 28


Pharmaceutical residues in wastewater are a well known concern.

Yes, but are those residues significant enough to have a biological effect when processed into compost/used as fertilizer?
posted by zamboni at 8:53 AM on May 28 [3 favorites]


Without derailing this thread too much, there appears to be a level of 'well we are going to have some residue of [insert pollutant here]' as if this is something which should be accepted as 'normal'. This is worrisome to the greatest degree as we are faced with a bleak future due to high levels of pollution which is known to impact the well being of the environment we all depend upon to exist. Even with the best will in the world, everyone reading these words will be long gone before the benefit of taking a stance, drawing a line in the sand, and saying enough is enough will benefit our descendants. That is assuming we actually try and alter our lifestyles by reducing our dependence and lifestyles upon a carbon/plastic consume, consume, consume lifestyles. Equally it assumes that there will be descendants of humans rather than the typical natural cycle of a species dying out and another becoming prevalent..
posted by IndelibleUnderpants at 9:12 AM on May 28


"Yes, but are those [pharma] residues significant enough to have a biological effect when processed into compost/used as fertilizer?"

I'm curious about this as well.

So much cropland in the U.S. is fertilized with manure from cattle and hogs that are chock-full of antibiotics and other medicines, yet I've never heard anything about those drugs affecting the composition of the plant foods grown there.

(But I certainly may have missed such news.)
posted by MrJM at 9:30 AM on May 28 [1 favorite]


MrJM at 9:30 AM

See here. But one source of information...
posted by IndelibleUnderpants at 9:36 AM on May 28


I was under the impression that carnivore shit is no good as fertilizer, but evidently I’m wrong. TIL.
posted by scratch at 11:16 AM on May 28




A low tech solution being used today.
posted by jellacious at 12:43 PM on May 28 [1 favorite]


There's a lot of things we can do with poo

Jinx, PowerNap, I was just about to post that link. Has anyone else heard of HydroThermal Carbonization?

Basically pressure cooking sewage to change its chemical composition and creating fuel or aggregate for things like concrete. Been meaning to read more about the topic.
posted by ishmael at 3:45 PM on May 28 [1 favorite]


Basically pressure cooking sewage to change its chemical composition and creating fuel or aggregate for things like concrete. Been meaning to read more about the topic.

I know the Swiss use something like this for their water treatment. They take sludge, put it through a self-incinerator, then the results go into a high temperature fluid bed incinerator which heats the facility. Once the sludge is ash said ash is reprocessed for the minerals that are left in it.
posted by Your Childhood Pet Rock at 5:10 PM on May 28 [1 favorite]


Two issues I know of with using sewage treatment for humanure are microplastics, and 'forever' chemicals i.e. PFAS. You can filter out a decent percentage of microplastics from the wastewater that goes out into rivers etc (if the sewage company can be bothered), but then they just end up in the remaining sludge that does then go out as fertiliser anyway, which then goes onto crops.

Plus fertiliser commonly has microplastics added to it deliberately in order to make it easier to handle and slow down the release over time.

PFAS, a group of 4700 chemicals are used to make products water and grease resistant - in teflon (PFOA, specifically), food packaging, waterproof clothing, and the building trade, and are much harder to filter, so they just go back out again in both the treated water and the sludge used for fertiliser. Since they don't degrade, they just accumulate in the food chain.

"The Centers for Disease Control and Prevention (CDC) found PFOA in in the blood of 98% of Americans, as well as in breast milk and umbilical cord blood.
...
A study funded by DuPont as part of a legal settlement with residents living near one of its Teflon facilities found that PFOA was probably linked to six disease outcomes: kidney cancer, testicular cancer, thyroid disease, ulcerative colitis, high cholesterol and pregnancy-induced hypertension."

Regulators worldwide have been trying to catch up to significantly reduce PFAS use, but they're not fully banned yet, and there's plenty of them out there already, mostly in our drinking water.

Human waste treatment is not a trivial process, and doing it (mostly) right costs money and time - while it is not an issue that many people care to think about, and the UK regulator is poorly funded and massively overworked. Bad practise is absolutely rife in the UK; I'd be amazed if the US is any better.
posted by Absolutely No You-Know-What at 7:32 PM on May 28 [4 favorites]


Here in austin, they sell something called "Dillo Dirt"

I attended the infamous Austin City Limits concert the year they had fertilized with that stuff. Every stage had a unique smell. I threw away a couple of pairs of shoes.
posted by credulous at 8:25 AM on May 29 [1 favorite]


Once the sludge is ash said ash is reprocessed for the minerals that are left in it.

So I take it that the process of cooking at high pressure doesn't separate out the PFAS? They have to do it as a separate process afterwards?
posted by ishmael at 9:28 AM on May 29


Persistent molecules get broken down by enough combustion, ishmael, but elements heavier than C, H, O are still there.

We’d be trying to keep some vital fertilizer elements that are hard to keep in the soil, and divert heavy metals and arsenic and so forth which are entirely natural but unhealthy for us to breathe and eat.
posted by clew at 9:48 AM on May 29 [1 favorite]


(That was not a good summary of combustion, and I could use a good one because exactly this has come up in real life recently. Chem teachers, help?

How could we do this without losing all the energy we spent fixing N?)
posted by clew at 9:56 AM on May 29 [1 favorite]




What I think this article (otherwise excellent) is missing is recognition that in many places, post treatment sewage sludge is already used as agricultural fertiliser. All sewage sludge in the UK is spread on farmland to my knowledge. It's even imported from the Netherlands (where it has to be incinerated and can't be used that way).

Nonetheless that isn't without it's problems, in particular as linked upthread there isn't really any way of getting microplastics out.

Just to give some context as to how sewage treatment works:

Sewage enters treatment works and goes through primary treatment. This is basically just gravity settlement where the heavy... material sinks and liquid is then either discharged (pretty rare in first world these days but not unknown) or goes on to secondary treatment.

Secondary treatment is basically a biological process where aerobic organisms break down the organic matter in the liquid. A combination of sand filters, aeration, and open oxidation ponds is used to give bacteria and archaea the opportunity to feast.

Tertiary treatment is anything additional done after that. Usually this focuses on killing pathogens (using chlorination followed by de-chlorination for example) and removing residual nutrients like phosphorus.

The sludge from the treatment process is de-watered and then either sterilised in order to be spread, incinerated, or used as input in anaerobic digestors to make methane as a fuel. What's left over after that is still excellent fertiliser and can be stpread.

60% of all UK sludge goes to anaerobic digestors so it's not exactly a niche technology.

Basically pressure cooking sewage to change its chemical composition and creating fuel or aggregate for things like concrete. Been meaning to read more about the topic.

This is called advanced anaerobic digestion. You raise the temperature to a few hundred degrees and the pressure to a few bar and then suddenly release the pressure. It blows open all the cells basically and gets much better gas yields.

Unfortunately while the output of advanced anaerobic digestion isn't going to contain pathogens, those temperatures and conditions are not going to do much about microplastics nor anything at all to PFAS.
posted by atrazine at 8:45 AM on May 31 [2 favorites]


So much cropland in the U.S. is fertilized with manure from cattle and hogs that are chock-full of antibiotics and other medicines, yet I've never heard anything about those drugs affecting the composition of the plant foods grown there.

Both home gardeners and commercial growers are actively worried about the effects of permitted herbicides as they pass through into cattle manure, and how that affects the resulting commercially-available compost.

Did I DESTROY My Garden With COMPOST?
Dealing with Grazon Contamination
NC State Extension: Herbicide Carryover in Hay, Manure, Compost, and Grass Clippings
Oregon State University: Herbicide-Contaminated Compost and Soil Mix: What You Should Know — and What You Can Do About It
University of Florida: Herbicide Residues in Manure, Compost, or Hay
posted by Lexica at 1:32 PM on June 1 [1 favorite]


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