« How Sustainable is High-tech Health Care? | Main | How to design a sailing ship for the 21st century? »


Feed You can follow this conversation by subscribing to the comment feed for this post.



A different but related technology is the 'constructed wetland', which has been used quite successfully to treat industrial wastewater as well. Thank you for this article, I'm an Indian, and I'd heard about the East Kolkata wetlands, but I'd never read about it in detail. Indeed, 'urban fish ponds' are an example of intermediate technology that E. F. Schumacher would have approved of with a smile.

I have just one request: could you do an article on constructed wetlands? You might like the book 'Constructed Wetlands for Industrial Wastewater Treatment' by Alexandros Stefanakis, if you decide to write an article on this.

David L


Love your work. Thought you might be interested in this Asparagus at Formby:


Plus Sewage farms in the UK were famous for tomatoes :-)

You didn't even need the seed

Take care

Michael B


Hi there

Again a superb idea - only you forget that not all we drop is organic. What about all the chemicals, medicines, heavy metals contained in our shit ?

They did not exist in such quantities when the low tech sewage treatment system was put into effect.

My guess is that if not the fish, then the population eating them would be poisoned if using this system on the sewage of any western City.

Nonetheless, it would be a great idea

Mitch Kennedy Co-Founder


Good morning,

First, I have to say thank you so much for your unique perspective, I look forward to every issue, and have purchased your paper-based archive for my friends.

I read with interest your historical look-back on fish farming from sewage treatment. I have a few notes I would like to pass along.

1) John & Nancy Jack Todd piloted a 1970’s - 2000’s effort called Ocean Arks International, showing how a site (homestead, town, etc.) could be circular with its water, soil and energy. The raising of tilapia was an integral part of that system. I do believe though they were directly composting "humanure” in dry toilets.

They also worked with the Chinese provincial governments on Baima Canal to restore it public open space by designing ecological sewage treatment systems. SAD endpoint …The Canal Dredging Lobby ended the project (possibly due to fear of loss of dredging jobs should this eco-technology takeover.)

2) In “Ethanol can be a Gas” by David Blume, he relates an integrated system for processing wastes , growing mushrooms, herbs, biodiesel, ethanol, and various food crops. Great read.

3) Solviva, is an exercise in intensive agriculture within an enclosed space and has some aspects of silviculture.

4) Tufts University (my alma mater) may pose a “competitor” for humanure/sewage - as a soruce of energy for public buses… ;-)

And while all this is great, I have to pose the other issue, not specifically discussed in your article. That of bio-accumulation of a veritable soup of pesticides, flame retardants, Fluorinated compounds (PFOS, PFAS) and heavy metals. In the process of writing my latest book, Detox for Everybody, it became painfully clear we have stuck our foot into the proverbial shit really deeply.

PFCs, having a Fluorine backbone, are particularly difficult to destroy / degrade / metabolize. Having been widely used as fire-suppressants at airports and military bases, the US is finding migration off those sites into streams and municipal sewer systems, then into the Publicly owned sewage treatment works. Here they accumulate in the sludge which in some states gets applied to agricultural land, mostly grazing/ pasture land. The ruminants eat the grasses which have taken up the PFCs from the sewage sludge, and these chemicals bio-accumulate in tissues (see attached graph).

I don’t really know a solution - so far only High temp incineration destroys them. However they have been linked to precocious puberty, infertility, and liver damage and certain tumor types.

My sense here is that a) we need to stop making things the wrong way, and b) perhaps develop plant/bio solution that can transform the Fluorine somehow, perhaps a to crystalline format.

Much admiration and a big hug,


Laszlo F.


I think the article misses a key financial point: only low market value fish tolerate such an environment. AFAIK carp, rudd, eel are increasingly processed and used in cat & dog food rather than for human meals. Yes - we could eat them, but we won't, this should indeed be treated as a form of nutrient & fertilizer production, rather than classic fishery. While fish consumption is somewhat constant around the world, it increasingly moved towards saltwater fish from freshwater species (I confess: I prefer saltwater fish as well). So yes - a good biological sewage treatment system rather than something that could yield important agricultural resources, the extra effort is generally not worth it for fish-producing fish ponds.

Thomas Reis


I loved to work for a festival compost toilet company and written extensively about the civilization leak: here a German article how the French used human waste for raising fungi - champion.(Italians still do it) http://energieblogger.at/champions-scheisse-und-das-geheimnis-der-franzoesischen-kueche_3506.html will blog your article!




Very interesting article. I used to work in an environment protection department. Some of the waste division staff talked about the drugs and chemicals in sewage that were cycling through into the wider ecosystem/landscapes. These included the contraceptive pill, chemotherapy drugs, antibiotics, a load of highly carcinogenic/mutagenic chemicals. I've no idea whether in a fish farming system, the fish would end up contaminated from both human excreta and chemicals used in the surrounding landscape and wondered if you could address this.

Thanks Scott.



One point in your article, doesn't seem to have been thought through - the farmers which fed water-grown plants to their livestock, which also had the "benefit of drawing out heavy metals from the water".

That's not a benefit, if you're feeding the plants to livestock, which humans then eat. Animals and many plants can't break down heavy metals, or sufficiently excrete them - they're toxic precisely because they build up in the body. The concentration then increases as you go up the food chain. Growing plants to draw our heavy metals can be good, but putting them into the food supply would slowly poison the people eating those animals.



You can forget about that idea in modern societies, because psychotropic drugs are for the most part not biodegradeable...
this is even true for potable water from wells beneath rivers.

One would introduce a substance return loop and "treat" even healthy people.

Jim Baerg


Since I have lived in Canada all my life, the first problem I though of when I started reading this article was that mentioned in footnote 17. Has anyone found a way to make this work through freezing weather?

About the high energy needs of high tech sewage treatment: When I took a tour of a sewage treatment plant in Calgary, I was told that the sewage went through an anaerobic digester & the resulting methane was burned to generate electricity. I was also told that the electricity from that was enough to run the treatment plant with a bit left over to sell to the grid.

This is a quite high tech system with the mechanical stirrers you mentioned & some UV sterilization at the end before some quite clean water goes back into the Bow River. Apparently most but not all of the nutrients get taken out. Someone else on the tour mentioned canoeing past the treatment plant & noticing that river bottom plants were more abundant downstream.

My understanding is that anaerobic digesters kill most of the pathogens in the sewage. I would expect that using that before putting the sewage into these fish ponds would be a good idea, bot for killing the pathogens & generating a bit of energy.

BTW Calgary does use an artificial wetland to treat storm water runoff from the roads. https://www.calgary.ca/csps/parks/locations/nw-parks/dale-hodges-park.html

The Illinoisian


Thank you for this article. As an environmental activist currently working to promote an Illinois law that will slow agricultural nitrate and phosphorus run-off into surface waters and aquifers, I read your descriptions of urban fish ponds with great interest. Though the vast majority of N and P run-off, as well as chemical run-off, comes from Illinois agricultural fields, urban wastewater systems also contribute to this problem.

My question has to do with pollutants that your article did not mention: pharmaceutical drugs. Perhaps the levels of such pollutants are much lower in Asia than in the US, but articles about US water quality often mention the high levels of some drugs in our water systems. Has such pollution been an issue in any other part of the world? And if it has been a problem, have any of these low-tech sewage treatment sites found ways to address that kind of pollution?

A second question relates to viral loads in sewage. In the US I’ve seen a few articles detailing how COVID-19 has been found in local sewage. Has this factor come up in any of your research? How does viral contamination compare with bacterial or fungal levels where the 2-week ‘starvation’ period strategy seems to keep bacteria and fungus from becoming a problem in urban fish ponds? Maybe I’m simply expressing one form of the “yuck factor,” but I’m very curious about these contaminants and the ability of urban fish ponds to address their realities.

Again, thank you for an excellent article. The photos, too, really brought the subject to life. Many of the urban ponds are very beautiful and that was something I did not expect to see.

Your work is appreciated.




Another example in France on Atlantic Coast at Rochefort ~20 000 people https://www.station-de-lagunage.fr/en/

It's also a bird refuge.

Thank you for your work!

Israel Walker


You simply cannot escape the politics.

In Victor Davis Hanson's "The Other Greeks" (ISBN 978-0520209350) in which the author posits that real backbone of ancient Greek democracy was not the highfalutin words of the intelligentsia, but good stewardship by many small plot owner/operator homesteaders instead of serfs.

The iron age British won independence from Europe largely because of tradition of archery, which was possible there because of long tradition of small plot owner/operator homesteaders instead of serfs.

Or the Dutch ascendancy in 1400's which was (with a little help from fossil fuels, as you've covered) due to the unique land conditions there allowing a long tradition of small plot owner/operator homesteaders instead of serfs.

Or Thomas Jefferson's intention that the U.S. be a land of yeoman farmers, each with their own small scale, owner operator homestead.

Or the ascendancy of the U.S. in the 19th century because after the genocide and relocation of the native population there were huge timber reserves and a multitude of small plot owner/operator homesteads instead of serfs.

Marx was right about some things and one of them was that the workers should own the means of production. There is no solution but a holistic one, and part of that simply has to be that those who work on and live on the land owns it instead of capitalists.

Aaron Vansintjan


Some responses to the comments:

#1 Thank you Rajat! I came across constructed wetlands and am now considering writing a piece soon about it. Thank you for the book recommendation.

#2 Thank you David L. This is an extremely funny anecdote.

#3 Thank you Michael B for the comment. I would have liked to address this more comprehensively, even though it is already addressed in footnote 25. Some points:

- From the studies done, there was little evidence that these chemicals caused problems for the fish. However, these studies were done in (a) low-income countries (b) before the 1990s, when such chemicals were not as prevalent. That being said, there are practical ways around these issues, as recommended by the extensive literature.

- Integrated decontamination, e.g., using water hyacinth and duckweed to absorb toxic chemicals.

- “lengthening the food chain”, i.e., feeding fish to livestock. This would decrease concentrations of toxic chemicals and ensure that we don’t eat them directly but “dilute” them through the system.

- By and large, conventional recommendations apply just as well to this system, for example, making sure that industrial waste is processed on-site, rather than let out in municipal public wastewater treatment systems. This is rarely done in the first place and one of the biggest sources of the problem. Primary and secondary ponds also break down many (but not all) emergent toxic chemicals.

- Some countries are trying to do very complex things like use UV radiation to break down chemicals. You can see however that as we increase the complexity of our socio-natural systems, the “solutions” increase in their complexity and energy requirements as well—a running theme on this website.

As is clear, the problem is much deeper. As I say in the article “We should ask ourselves if it’s really worth it to permit these products if they make it harder for us to mend the ecological rift between our settlements and their surroundings.”

For more on this, I highly recommend the following texts:

Edwards, P. (1992).  Reuse of human wastes in aquaculture: a technical review.  Water and Sanitation Report 2, UNDP-World Bank Water and Sanitation Program, The World Bank, Washington, D.C. 350 pp.
WHO. 2006. Guidelines for the safe use of wastewater, excreta and greywater in agriculture and aquaculture.
Mara, D. (2013). Domestic wastewater treatment in developing countries. Routledge.

#4 Thank you Mitch Kennedy for the analysis and links. I’ll look into these, and hopefully they can inspire future pieces!

As noted in my response above, bioaccumulation of emergent chemicals is a serious issue. My above comments also apply here. As you note even conventional systems are having trouble dealing with these chemicals. A serious rethink of how we approach health and industrial production is of course necessary.

#5 Laszlo: Agreed that the finances are increasingly difficult. I had hoped that this was partly addressed in my point near the end about high-energy, high-input industrial agriculture systems. Currently it is simply cheaper and easier to raise fish on industrially-produced fertilizer and “trash” fish, a byproduct of oceanic industrial fishing. There are still cases, however, where this is still economically feasible, as in the Kolkata case.

Even so, there are many things we do as a society that aren’t for the purpose of profit alone; libraries and schools are one example. Likewise, fully recycling our nutrients should ideally be seen as a good, not a commodity. As you say, we should be looking at this as a means to (a) defray costs of wastewater treatment (b) nutrient recycling, rather than a fishery in itself.

#7 Thank you Scott, very important point. See my responses to #3 & #4.

#8 ET: The problem is more complicated than that. Currently, in the Hanoi case for example, since the fishpond system was stopped, there has been no adequate sewage treatment, industrial or municipal, to speak of. Therefore bioaccumulation and contamination is already the norm.

Because of this, WHO guidelines suggest acceptable levels should be a goal rather than a requirement. This is because for low-income countries, any intervention is better than nothing, which is the status quo. What’s more, there is good evidence to show that bioaccumulation is actually not that serious in these systems, rather, what they seem to do is “dilute” it to more acceptable levels through lengthening the food chain. So, rather than rejecting this system outright, it would make more sense to keep the broader goal in mind (water treatment and recycling nutrients) and encourage cheap and doable interventions to lessen negative impacts (e.g. regulate the same water plants should not be fed directly to livestock or be the main part of their diet, rather, they would need to be used as compost / fodder for crops first, therefore “diluting” heavy metals; treat heavy metals on-site in industrial production; use primary and secondary ponds to “settle” heavy metals when possible).

See especially Mara, D. (2013) (free online) for more on this.

#10 Thank you Jim Baerg. I wondered the same, but haven’t found much information on it. Interestingly, since I wrote the article, several people have told me there were some sewage treatment plants in Ontario, Windsor I believe, that used fish. I am curious if they are still around, and how they dealt with the cold weather problem.

There are many solutions for treating sewage, which range from the complex and high-input to less complex and low-cost. By and large, as I understand it, there is a trade-off between high-input and high-cost treatment that take up less space, and low-cost and low-input treatment that takes up a high amount of space. For most countries, allowing the wastewater to settle in primary and tertiary ponds deals with almost all the pathogens and allows the heavy metals to settle, and UV from the sun can break down a lot of the more complex compounds—similar to the anaerobic digester. It is here that the fishpond system might make the most sense, because it has low initial capital investment for the amount of environmental benefits it provides. For high-income countries, more complex systems have diverse benefits, and it may make sense to do capture the methane and burn it to generate electricity. Even then, though, there is still the problem of eutrophication downstream, and fish (or wetlands) could still complement the system.

#11 Thanks Illinoisian! Thoughtful reflections and I’m glad you find it interesting for your work. I dealt with some of your question in my response to (3), (4), and (8). I would add this to your specific question about COVID-19.
Fish ponds can be considered one addition to the conventional sewage system, which already involves primary and secondary treatment ponds that retain sewage for at least 2 weeks. This deals with the majority of pathogens, and likely also kills COVID-19 for the same reasons that it kills the common flu, largely through exposure to sunlight in the case of this pathogen. The same recommendations for conventional systems apply to fish pond systems, by and large. The difference between conventional systems and the fish ponds is that they also aid in the recycling of nutrients back into the system rather than causing eutrophication, and, second, can help offset the cost of sewage treatment.

I would also recommend that you read Mara, D. (2013) (free online) if you’re curious for more, the last chapter deals with fish ponds, but the rest of the book is about the science of how to deal with contaminants and pathogens cheaply and effectively.

#12 Torcy: thank you, that’s very interesting!

#13 Thank you Israel Walker for the interesting comment. I would definitely agree that those who work on and live on the land would own it—just as workers should control the fruits of their labour. Land reform is fundamental to the change we need. I don’t think small landownership necessarily solves all problems, it was also part of what helped build the popular base for the genocide of Indigenous people in the Americas, for example and, coming from the low countries myself, Dutch individualism was also part of the ascendancy of capitalism. And there remains the question of how smallholder farming can still perpetuate oppression of women, especially if women are not also given the right to the land themselves. You might have already come across this, but I would highly recommend Chris Smaje’s Small Farm Future which provides an interesting reflection on these themes.

Jim Baerg


Israel Walker: have you read about this guy's ideas?



"The iron age British won independence from Europe largely because of tradition of archery, which was possible there because of long tradition of small plot owner/operator homesteaders instead of serfs."

Israel, I'm sorry to start an argument in a comment section, but this is a-historical gibberish. It's beyond the pale.
1) Britain cannot win independence from Europe, it is and will always remain part of the continent of Europe.
2) If you're talking about the English Longbow (it's actually Welsh), that was a medieval weapon, not from the Iron Age, nor was it used to liberate anyone (it did nothing for the independence of Wales), but was used mostly to occupy France.
3) Longbows have nothing to do with small plot farmers. Bowmen were professionals, and farmers don't leave their farms to go on military campaigns in France.
4) Britain has zero tradition of small plot owner/operator homesteaders. Medieval Britain's farms were worked collectively by villages under common ownership. Private ownership did not become normal until the 18th century Enclosure Acts, when the Aristocracy took the land into private ownership (i.e. stole it) and booted all the peasants off into the cities.
On other matters ...
5) The ancient Greeks were slave owners who swanned around while Helots and debt-slaves worked their farms. Their sense of common political action came from anti-slave action groups like the Crypteria -- compare the KKK and the democratic party in 19th C. history.
6) Serfdom was a fiction invented by Karl Marx to make history fit his woo-woo theories. If it ever existed anywhere it was in 18th century Poland, not Medieval Europe.
7) America's Homestead Acts were good advertising to get people to emigrate from Europe, but 70% of land given out in the Homestead Acts was not suitable for agriculture and was abandoned. And we can quibble over whether the 160 acre and 640 acre plots that were given out count as 'small holdings'. After Jefferson's time, the land grants were really just political cover for private railway builders taking public land, and various other kinds of looting.
8) Thomas Jefferson and his fellow travelers were slave owners sitting on gigantic plantations. They had a great line in bullshit, but it deludes people about America's political history to this day.
9) America's rise in the 19th century was entirely due to industrialization and the growth of the massive cities in the north east.
10) Karl Marx was 100% wrong about everything.
11) Workers are entirely free to own the means of production at the moment, if they want to. They can set up their own companies run by the workers. The don't because most people have enough life experience to know that running a business is not a joke. It's not something you can do over a tea break on Friday afternoon. In fact sometimes, people actually do set up businesses just like that, in almost every recorded case they have failed within a few months.



As the other commenters already noted, accumulation of Pharmacutics makes this likly unviable for modern western citys.

(Pre-)treating the water with plants still remains viable though, depending on the contamination, they can then only be harvested for use in Biogas production.

Also do note, that open water surfaces can give rise to the Mosquito population. If a society has to decide between Zika and Malaria or not having a fishfarm, they will opt against locally produced fish.

Also to quote the 2010 Article: Recycling animal and human dung is the key to sustainable farming


from the Section: Composting

However, Duncan Brown is more critical of their composting techniques. The health advantages that the Chinese gained by keeping their drinking water supplies clean, were partly offset by the transmission of diseases via food crops:

"Gastro-intestinal diseases were endemic throughout the region. In Korea and Japan, fluke diseases were common because of the practice of eating raw fish grown in ponds fertilized with human excrement. But those diseases could have been largely avoided with a better understanding of their nature and modes of transmission. If properly used, devices like the relatively modern sceptic tank, the more modern oxidation tank or the so-called composting toilet can avoid the danger of gastro-intestinal diseases previously associated with the use of human excrement as manure."

So as stated there, composting is the more secure way of using Humanure. And if it is naturaly composted, you should not use it for crops where the manure makes contact with the product, so no fish or vegetables, but instead fruit trees or energy crops.

Jim Baerg


Somewhat relevant to your post, since treated effluent from the town & meat packing plant go into the lake to both feed the wildlife & further treat the effluent. I'm a bit unclear on how well this further treatment works during winter.
I visited it today, & the bird life is *very* abundant & diverse.
"Water control measures have been implemented to help ensure that water levels are maintained. Measures include the building of dikes and water control structures as well as the building of a pipeline from High River to channel treated effluent from the town of High River and a local food processing plant. Water quality is regularly monitored."



By rule of thumb and by historical experiences, we should not mix our food supply and our s*it. I believe that there is maybe not so low tech solution, but still pretty low tech one. Either trickling filter or something known as Schulz's filter, it is some 5 m tall steel cylinder of some 1.6 metre in diameter and it is filled with stones over which sewage without large particles is poured. Then microbes take care of all the filtration.

Cavan Mejias


After reading your very convincing essay on low-tech processing of sewage I found these two resources.

On the subject of fish farming this video describes treating the effluent water of such a setup with vetiver grass (Chrysopogon zizanioides) https://youtu.be/VOHq4HrtxtI

Additionally this video of sewage treatment involves vetiver grass growing floating in the ponds, https://youtu.be/7u4DhmRY9Fo?t=140

Thank you.

Cavan Mejias


The effect of modern pharmaceuticals on the low-tech sewage treatment described in the article has been raised repeatedly in the comments.

I found this recent research on 'removing antibiotics ciprofloxacin (CIP) and tetracycline (TTC), and nutrients, N and P, from secondary wastewater effluent' that utilizes vetiver grass.

The report (titled Removal of Antibiotics and Nutrients by Vetiver Grass ( Chrysopogon zizanioides) from a Plug Flow Reactor Based Constructed Wetland Model) can be found here https://pubmed.ncbi.nlm.nih.gov/33921009/

Keep up the good work!



Would be a big mindset change but you could separate solids and liquids at the source (house/apartment). Then use it as a resource. Solutions to do this could be low tech and adapted to the particular environment. Uses could be local or regional. Could be done safe way.

A few things that comes to mind - collect urine, pasteurise it, then spray it as a fertiliser on farm fields. Or dilute urine and put it on your own garden. Solids could be put under fruit trees - as long as covered with a reasonable amount of mulch. Use biology (active soil or fungi for example) to pre-digest the solids.

Cavan Mejias


Following on from Barney's comment here is a short video entitled 'Vetiver latrine in Busia, Kenya' from The Vetiver Network International. It describes how to use a small vetiver constructed wetland to treat waste water from latrine in rural Kenya.


Thank you for reading.
Best Regards

The comments to this entry are closed.