Post APlOFvseAjkJ6rt7gW by tfardet@scicomm.xyz
(DIR) More posts by tfardet@scicomm.xyz
(DIR) Post #APlOFslRl3ChRfUpXs by tfardet@scicomm.xyz
2022-11-19T13:41:36Z
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Time for a thread about my new research topic: #nutrient flows!I started looking at #nutrients and #agriculture a while ago and was appalled by the current situation of our agri-food system:from a mathematical standpoint, if you want #sustainability, you need to bring back the same quantity of nutrients you extracted during harvest, right?To grow food it's a little more subtle than that, but broadly, you want a circular system.Do you know how far from circularity our food system is?1/N
(DIR) Post #APlOFtWavkuxntYU2C by tfardet@scicomm.xyz
2022-11-19T13:41:50Z
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When you start looking into it, the dominant agricultural system is somewhat puzzling:1. plants need fertilisers so we make them - this costs a lot of energy and fossil fuels to make NH3 from atmospheric N2 - it required mining for phosphate rocks and potash2. we eat some of the plants, give the other to animals3. we eat the animals or something they produce (e.g. milk)And then what happens to the nutrients?Can you guess?2/N
(DIR) Post #APlOFu01AMSBH9Jytc by tfardet@scicomm.xyz
2022-11-19T13:42:11Z
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Then, nutrients are excreted in urine and feces: - for animals, some is recovered as manure - the rest is mixed with water and goes to water treatment plants - there, we pay a lot of energy to convert the N to gaseous N2 and send it back to the atmosphere - for P and K, it is slightly better, as a part is recovered in the sludge and used on parcels... - but it has been contaminated by wastewater pollutants (including heavy metals)Your standard linear, extractive system.3/N
(DIR) Post #APlOFvOrxRvVcVxLGq by tfardet@scicomm.xyz
2022-11-19T13:43:12Z
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The whole system is actually an agri-food-excretion combination.By treating them separately, we are creating a few (!) problems with the whole system:a) We don't have unlimited energy, nor gas, to resynthesize the usable nitrogen we "destroy" (especially now)b) Phosphorus and potash mines are finite resources and the current system is sending precious nutrients to the sea!c) Nutrients not recovered in water treatment plants pollute water streams and coasts (ever heard of algal blooms?)4/N
(DIR) Post #APlOFvseAjkJ6rt7gW by tfardet@scicomm.xyz
2022-11-19T13:43:33Z
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So how do we solve this?Today we use around 100 Mt of N, and 40 Mt of P and K a year worldwide.https://ourworldindata.org/grapher/fertilizer-use-nutrient?country=~OWID_WRLWe have very low efficiency for their application, though, so while African soil does not get enough nutrients, there is a large excess almost everywhere else.Recovering human excreta (around 30 MtN, 3 MtP and 5 MtK), coupled with food scraps/waste reuse, better efficiency, and more plant-based diets, would go a long way towards making our food system more sustainable.5/N
(DIR) Post #APlOGAFqjGclgsqqnI by tfardet@scicomm.xyz
2022-11-19T13:43:56Z
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But how do we do that?How do we move from a situation where we recover only a few percents of the nitrogen and barely half of the phosphorus, to something that get's close to 100%?Can/should we move away from a combined sewer systems?Is it compatible with a world where most of the population lives in dense urban areas? (recovering human excreta there is no small feat!)What are the associated problems, costs, and benefits? Is it safe from a sanitary perspective?6/N
(DIR) Post #APlOGSBY3zsZIkyfaa by tfardet@scicomm.xyz
2022-11-19T13:44:16Z
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Well, stay tuned, I'll discuss these points in the future ;)I'll just finish here for now, and end this thread with a nice quote from Asimov: "[W]e may be able to substitute nuclear power for coal, and plastics for wood, and yeast for meat, and friendliness for isolation -- but for phosphorus there is neither substitute nor replacement".7/7, the end!
(DIR) Post #APlOe2kWHkY1MaaF4i by strypey@mastodon.nzoss.nz
2022-11-19T13:52:50Z
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@tfardet > recovering human excreta there is no small feat!Here's an example of a novel way of turning humanure into a useful product: https://www.goodnet.org/articles/you-guess-what-fuels-uks-new-sustainable-bus> Is it safe from a sanitary perspective?It's not generally mentioned in articles on this version of the BioBus, but making biogas renders the remaining material biologically inert, so it can be safely used to make fertilizer.
(DIR) Post #APlPBWc8GnMTXkcrDs by tfardet@scicomm.xyz
2022-11-19T13:58:50Z
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@strypey yeah, I'll discuss anaerobic digestion versus compost, notably ;)As for the sanitary part, there are major differences between urine on its own and feces or mixes of both, but it's all manageable.