The Liquid Trees Of Belgrade: The Facts Behind The Furore

Historically, nature has used trees to turn carbon dioxide back into oxygen for use by living creatures. The trees play a vital role in the carbon cycle, and have done so for millennia. Recently, humans have thrown things off a bit by getting rid of lots of trees and digging up a lot more carbon.

While great efforts are underway to replenish the world’s tree stocks, Belgrade has gone in a different direction, creating artificial “liquid trees” to capture carbon dioxide instead. This has spawned wild cries of dystopia and that the devices are an affront to nature. Let’s sidestep the hysteria and look at what’s actually going on.

Green Goop

It’s perhaps understandable why the so-called “Liquid Trees” have caused so much consternation. Much of that may be down to their futuristic, cyberpunk aesthetic. The devices consist of eerie green fluid in a transparent tank, lit from inside. They looks like something straight out of science-fiction, which naturally leads people to connect with the scary tropes of such media.

The layout of the Liquid3 bioreactor. Credit: Liquid3

In reality, though, the devices serve a real and positive purpose. The photo-bioreactors, as they are technically known, are air quality control devices built specifically to suit the urban environment. Inside the tank, microalgae is grown in 600 liters of water, using CO2 from the atmosphere combined with photosynthesis to produce oxygen and biomass. One LIQUID3 bioreactor is capable of replacing one 10-year-old adult tree, or a full 200 m2 of lawn. This is of huge benefit, as the bioreactors can be built and installed far more quickly, and start processing polluted air immediately.

Like trees, the devices are solar-powered, with panels on top to capture light and turn it into electricity. Built-in lighting allows the microalgae to photosynthesize year round, even in the dimmer winter months. There’s also a pump which captures polluted air and bubbles it up through the water to feed the algae. The LIQUID3 bioreactors are built with an eye to civic duty, as well. They’re constructed to also serve as city benches, while also providing a power outlet for charging mobile phones.

There’s a pleasing glow to the bioreactor when powered up at night. Credit: YouTube/UNDPSerbia

The bioreactors are well-suited to the built environment of Belgrade, Serbia. The city is subject to significant air quality issues, with high PM2.5 counts by virtue of two neighbouring coal power stations. Serbia as a whole records 175 pollution related deaths per 100,000 people, making it Europe’s worst performer by this metric. It’s also 33rd in the world for having the worst air quality.  Anecdotally, activists complain of pollution so bad that it can be readily detected by sight, smell, or taste during the worst periods. If you were in Beijing in the winter of 2015/2016, you’d be familiar with the flavor.

Much of the uproar towards the devices is misguided. The bioreactors aren’t intended to replace urban trees with scary-looking machines. Instead, they’re designed to slot into spaces where growing a tree is impractical. Plus, the microalgae bioreactors offer efficiencies that trees and grasses simply can’t match. Microalgae can be capable of removing CO2 at a rate 10 to 50 times faster than even mature trees, to boot. Once grown, the microalgae can be harvested and used as a potent fertilizer, as well.

As valuable as efforts like the Trillion Trees project may be, there’s something to be said for the sheer practicality of building compact bioreactors. The fact that they start capturing useful amounts of carbon dioxide from day one is just a further mark in their favour. As the world struggles against rising carbon levels in the atmosphere, expect to see bioreactors like these proliferate in cities around the world. They may just be a key weapon in the fight against climate change, while also transforming our urban spaces into the futuristic cityscapes science-fiction had promised us.

126 thoughts on “The Liquid Trees Of Belgrade: The Facts Behind The Furore

  1. No analysis of the CO2 released during manufacturing? I’ll pull my own numbers then, 1-2 tons of CO2 during manufacturing seems reasonable estimate, and maybe 100 kg captured per year. So let’s hope these are designed to be very durable and long-lasting.

      1. Plexiglass

        2cm thick, 1m x 1m, x2.5 = 0.05m³
        0.05m³ x 1.18 g/cm³ = 60kg

        60kg x 5.5kgCO2/kg = 330kg

        Solar panel

        300W x 2560kgCO2/kW = 768kg

        Bench & frame (solid acrylic countertop perhaps)

        100kg * 8.9kgCO2/kg = 890kg

        Comes out to 2000kg CO2. 2 tons is the right ballpark, and honestly my estimates here are conservative & don’t consider lots of additional stuff like R&D and installation & disposal CO2. If the creators were being honest, they’d put these numbers up front. But they know it just doesn’t add up, so they don’t.

          1. Probably China like most of the “green energy” components. Meanwhile, they build more coal fired plants annually than the rest of the world combined. Go to China on a griping campaign, Greta, point that out, and see what happens to you.

          2. Eyeballing it. plexiglass is a commonly used clear plastic & the bench+wall material looks very similar to the countertop I see in many commercial bathrooms. I don’t care about being 100% right, just aiming for the right order-of-magnitude.

        1. Well, that doesn’t sound good.

          If you really want to be fair though you might consider that there probably would have been some more traditional bench, display or decoration on the spot which would also have released CO2 in it’s production. Maybe not much if it’s ‘just a bench’ but some other sort of sign, decoration or display might have included pretty much every other component the ‘liquid tree’ contained except for the algae.

          Also.. this wasn’t primarily an energy generation project so not entirely applicable. But the anti-green energy people are constantly going on about the CO2 released in producing a solar panel. But.. they aren’t taking into account the CO2 being released to produce whatever the panel is replacing. Also, they seem to be assuming all the energy used to produce green energy devices can’t itself be green. If you have a factory pushing out solar panels as fast as it can, which are then going into production feeding into the grid then the more you fill the grid with your product the greener the energy coming into your factory becomes. That’s not really an argument for producing fewer solar panels.

          1. The issue with new green tech is if you’re (as is often the case) replacing existing tech that would otherwise continue in service, then the manufacturing CO2 of the item you’re replacing isn’t relevant.

            In this situation, we can probably discount the bench and installation costs – a tree would also require installing, and might have a bench under it. Unless of course the stylish bench is considerably worse than the typical benches that get installed.

            But, yes, the CO2 costs of installing it aren’t free. It’ll also require servicing, though perhaps no more than a tree would.

            But the key things here are that it’s going where a tree wouldn’t fit, and that it’s also improving air quality.

            …and that it requires electricity… is it a net producer or consumer?

            Honestly I’d remove the solar panels. I know they’re there to make it “tree like” but it’s far more efficient to not manufacture them, and use wind turbines elsewhere to make the electricity.

          2. Or anywhere else.

            The main issue with PR projects like this is that politicians are very eager to buy them, but very reluctant to allocate any money or people to maintain them. Anything that represents a one-time cost that can be tied to a campaign is a good thing, but the upkeep cost is just dead weight that doesn’t buy any more votes, so most such projects are launched with great fanfare and then abandoned to decay.

        2. This is interesting, but doesn’t do anything to dispute the location of the CO2 being collected here and what would be in the same place without it.

          Even if we disregard this however, there is no reason these cannot last 10-20 years and and least break even, let alone if more sustainable materials are used.

          These projects are but always good enough, but moving in the right direction is important.

          1. It’s another question entirely whether they’ll keep them for 20 odd years, instead of replacing the tank with an advertising billboard next time the city starts running out of money.

        3. I love it when armchair experts try to ‘debunk’ the feasibility of prototype, specialised hardware using sweeping assumptions about design, implementation, and purpose trying to back their arguments up with ballpark estimates based off decade(s) old research that, nevertheless indicate fairly reasonable numbers that are at least an order of magnitude off, don’t you?

        4. 20 years to break even and a few more to actually offset other things doesn’t seem like a completely ridiculous longevity target, I know soda machines older than that.

        5. I agree… It is discouraging to see scientists not be forth coming with short comings. Maybe the technology is worthwhile. I just want honesty and through analysis. Science is polluted with politics and social justice. Sad. Thank you for your analysis.

      2. Just plant trees ….. they bring a whole biological eco system of insects etc. This plastic box overlooks the water transpiration and cooling effect that trees bring as well as natural shade and keeps people in touch with nature.

          1. Unfortunately it isn’t that simple – trees and their roots are just not practical or safe everywhere in a built up area. Not going to argue against more plants in cities where it can be done, but this bench potentially at least is a way to get some of the benefits without the drawbacks. I would say its a good supplement at the very least.

      1. I love how all these super-obvious greenwashing campaigns which will never lead anywhere can simply neglect to publish figures on important aspects of their work and then faithful people online will attack anyone who speculates about them instead of the super-obvious greenwashing campaign which will never lead anywhere

        1. Welcome to the Gartner Hype Cycle. We are now climbing towards the peak of inflated expectations, please make sure your safety bar is all the way down and locked before we go over the top.

      2. Then tell the manufacturer to provide honest numbers so we don’t have to estimate them ourselves.

        P.S. There’s one comment that shows a very reasonable well-thought-out estimate of 2 tons CO2. You can see the calculation steps.

  2. My only question would be, how many years of operation does it take to fully offset all the carbon dioxide released during the manufacture and transport of the entire device ?

    1. Don’t forget the extra CO2 released by service and maintenance of these things. Trees in urban environments also not maintenance free, but I suspect these things are higher maintenance as soon as I read “solar panels, lights and pumps”

      1. People often discount the maintenance costs of living organisms, particularly domesticated ones and in urban environments. The fully burdened cost is much higher than you would expect, as there’s a lot more work to keeping a tree alive than just “dig a hole, dump dirt in hole, jam a sapling in, do nothing for decades”.

      1. A weird assumption, as it is clearly stated in the article that the solar panel provides the light and additional power to charge usb devices, and reasonably, the very low power to run the “pump” (which is more aptly thought of as a fan, as it just inserts environmental air into a bubbler (like a fish tank has) in the bottom of the tank). Or do you think your “assessment” of the solar panel output is better than the people who were paid to design this?

  3. the discussion of CO2 is ridiculous. if it’s a CO2 capture technology then you’ll want to do it in vast ponds at an industrial site away from the city. scale effects would be the only effects.

    i wonder if it’s actually any good at particulates. if it is, that’s a real value to a city. i kind of suspect that it isn’t a great solution for particulates, that it has air intake filters that need regular cleaning and you could get the same effect from just those filters. but i don’t know.

    but obviously, it’s public art. nothing against weird public art.

    1. The biggest problem with CO2 capture is dilution. Even at unnaturally elevated levels that fuel warming CO2 is still just a small part of the air. So to remove a significant amount one must process a LOT of air. It is very inefficient. That’s why most effort is on not releasing it in the first place and most carbon capture projects that do exist are things to mount on smokestacks.

      That said they are going to get a slight efficiency boost by building their project in the city where they are closer to the source of more of the CO2 and so it is a little more concentrated. Maybe not much.. but it’s still a benefit over doing it in a site away from the city.

      As for particulates.. I assume they are bubbling the air up through the water right? I would imagine most of the particulates would end up in the water that way. They used a water curtain to contain paint overspray at a factory I worked at many years ago. I imagine it would work about the same way.

    2. Looks like they are just bubbling air through the algae tank, which should be pretty good at capturing particulate really even if there is no intake filter, which there probably is so the algae havest is better more valuable fertiliser and the tank cleaning stays easier…

      And it will take some carbon dioxide out of the local air, which is probably a very good thing for those living there. So a discussion on it as an improver of air quality locally is definitely on, and as a CO2 capture tech it may well actually work out just fine too!

      Cities need better air quality so you are almost certainly going to be building something to filter the particles out, cities need bench, again you were building them anyway, seems like it has a power bank charge your phone function too – another thing that will be very useful for many. The Solar setup in this design I’d suggest is at least a nominal 330-500 Watt panel (maybe even two) as an awning over the bench, which really should be plenty for running an air pump – it might well be a net gain for the grid (if it is connected). So the cost increase of this vs doing all the stuff it does without the algae is probably quite small. And then by using the algae in place of more industrial produced fertiliser (or potentially even just directly eating the algae – some of them are edible) I would expect a substantial CO2 saving, and it certainly can end up with much of the CO2 it captured remaining in the soil or bound up in the flora and fauna more widely long term – put it in the right places and it could be increasing the carbon captured in biomass for that area practically forever. If not actually ‘forever’ captured – can always sun dry it and dump it down a deep dark stable hole somewhere)…

      Obviously I’d love way way more details to actually have any hope of doing a more proper analysis – but it could be really good at carbon capture when viewed across its full range of effects and impact. I’d expect it to be more neutral than that, but there are so many details lacking to make a good analysis.

      1. As someone who lives in a city, in all likelihood the USB charger point will be broken almost immediately, the whine thing will be covered in scratches and graffiti within months, and people and their dogs will pee on it. And it will probably be about as functional as the toilets in a public restroom within three years, meaning it’s a coin toss whether it will work at all. Maybe it would stand a chance on private property somewhere, or as part of a museum.

  4. This would also be great for an accent wall in a livingroom lets say, or a foyer “art piece”. Could the air quality enhancing properties of this be useful in a residential environment? Use the removed Biomass as a fertilizer for your lawn and garden? I really like this idea and think you could totally put some effort into design and come up with a viable in house design element.

    Watch out for my kickstarter.

      1. Not as much as you might think. With the air bubbler, it stays mostly aerobic, and minimizes the anaerobic processes, which are far smellier. Also, the bubbler creates a positive pressure in the tank, which would be vented out the top quickly enough that odors wouldn’t intensify.

  5. If the algae is then used as fertilizer, it’ll just release the CO2 back into the air.

    It might be better than our current methods for making fertilizer. But unless we somehow sequester the algae, this is just the same old carbon cycle, isn’t it?

    1. It may release CO2 back in the air, but away from Belgrade… It’s more a device to move CO2 away. If the area cannot sustain trees, you stick one artificial tree to do the job, harvest the CO2 and move it to some place else.

      1. Is there so much CO2 in the air in Belgrade that the CO2 is an air quality problem for humans there? I think CO2 becomes directly harmful for humans at around 1000 ppm, while the world average is 415 ppm. Data I’ve seen from Korea (Seoul is supposed to be number one in the world for CO2 emissions) suggests something like 40 ppm variation between hotspots and average levels, at least at airplane altitudes. I couldn’t find data on ground-level variation. Is there really 1000 ppm in Belgrade?

        I would think that particulates are the main issue at the local atmospheric quality level, not CO2. On the other hand, CO2 is a problem at the global climate level, but pumping it out of cities doesn’t seem to help wtih that.

        But all this is not my field.

    2. I find that …. curious as well.

      It’s like playing catch and release. If the goal is improving local air quality, that’s one thing. But if it’s carbon capture, they’re going to fail at that.

      1. No one claimed this was a carbon capture scheme. It is to clean local air, add a little beauty, make a bench more useful (including a charging station and light), in a small urban space.

      1. Feeding the third world will NEVER allow us to cease using industrial fossil-fuel-derived fertilizer. It will not happen without letting billions starve (and they eventually will).

      2. >“It might be better than our current methods for making fertilizer.”

        Unfortunately fertilisers tend to be nitrogen, phosphorus, and potassium, none of which the mciroalgae are going to get in any real quantities from the air. If there are nitrogen-fixing bacteria in there that might help, as long as they don’t compete with the algae, but otherwise the system is going to need fertilised itself. In other words, this isn’t a better way of making fertiliser, it’s just an extra step to convert fertiliser into algae before the algae are used as fertiliser.

      3. The issue is that these algae also need (artificial) fertilizer to grow. Algae capture CO2 and produce an oil (similar to olive oil) which can be used as biofuel. They are quite efficient in turning co2 into biofuel. However the amount of fertilizer (minerals) needed for them to do that costs about $35 dollar per gallon produced. Fertilizer for any crops are mostly made from minerals you dig up in mines.

        Another way of looking at it: it costs about $35 dollars to capture the amount of co2 produced by burning 1 gallon of diesel fuel…. And to capture all the co2 produced by humankind per year would need about a standard sea container sized bioreactor per person…. So about 8 billion of them…

        1. In biofuel production, the idea would be to separate the minerals out of the ashes left over and feed that back into the tank. After all, you only need the carbon and the hydrogen.

          1. And how much would that cost as opposed to buy cheap fertilizer? This is one of the main reasons why biofuel produced in this way is not economically viable.

  6. What the Felgercarb is this? Use it for fertilizer? Where you grow carbohydrate things that get eaten and turned back into CO2 and water? What am I missing?

    World wide forestation has increased 15% since 1985 and population is stabilizing and decreasing in most of the World. I really don’t understand the panic.

    1. while i agree that this whole thing is completely useless apart from looking cool the panic would be the people dying from lung disease in Belgrade due to pollution. oh an yeah the little thing called climate change… maybe you heard of it?

          1. First you got to be honest yourself.

            “Weather is not climate!”, they say whenever there’s a cold spell and the pundits start talking about how global warming got cancelled. “Look at the hot weather, it’s climate change!”, they say when the opposite happens. Heads I win, tails you lose.

            You can’t play by two different rules at the same time and expect anyone to trust you.

  7. Sometimes people cant see these things for what they are, a disguised means of lining someone’s pocket, hidden under a virtuous veneer.

    The amount of CO2 required to produce these AND the amount of CO2 required to keep these maintained readily outpaces the amount of CO2 offset by the installation of these. It will be well over a decade before these devices become carbon neutral.

    Its yet another grift to take the Serb peoples’ money.

    1. Exactly. Climate damage IS real, and the 95% of people talking about solving it ARE cynical liars. Both are true. I wish more people could understand this. The largest man-made methane emission in history was the sabotage of the nordstream pipeline. Crickets from EDF, because they are part of the American imperial grift.

  8. This is an unfortunate marketing gag.
    Not usefull for anything else. Maybe plant some trees, so that they can do the carbon capture in 10 years when they are grown.

    They will also:
    – be much, much cheaper
    – give shade in the summer and regulate the temperature of the urban environment.
    – regulate humidity
    – filter polutants, improve air quality
    – improve quality of life in the city
    – not use electricity during winter or at any time.
    – not produce co2 during production.

    This is recognized by many as a cyberpunk dystopia, because it is exactly that.

    1. You won’t get me arguing against more ‘real’ plants in cities, but vast areas of the city can’t be filled with plants bigger than the flowers in a hanging basket at all practically. This could be a very good substitute for those areas of a city where a tree would be too big, its roots to destructive etc.

      Also as these are designed as bench – something cities need anyway so only the increased CO2 cost should count against the algae concept for a new bench, and sheltered it would seem by solar panel, which if grid connected or just used to power the local street light will add up quite a bit across the city. And then on top of that produce a fertiliser that isn’t stupidly carbon intensive the way industrial produced fertiliser tends to be. The CO2 saving in their lifetime could be very real – more details wanted, but it isn’t implausible.

      Also worth pointing out that as you can in theory cycle the algae and keep this structure unchanged for centuries with a few pump replacements it will over that time capture way more than most city bound trees – they will get cut down and replaced or heavily trimmed with the cuttings most likely chipped and burned many times for public safety type reasons. So the tree may well be the less ecologically sound option when in a city.

      1. Terraced roofs are very common in cities, accounting for up to 2/3rds of the roof area. They can be planted with small gardens and even trees.

        Another solution would be to decrease the people density so you can fit in a lot more parks and boulevards with greenery. After all, the modern city is an artifact where the vast masses try to make a small living by exploiting the consumption of services by other people, often by people poorer than themselves who are simply paid welfare to shut up and stay put (and vote for social democrats).

        The city itself doesn’t produce anything, there’s little opportunities for real productivity that returns its own cost – it’s just where everything ends up because of the concentration of commerce. The city is just a big “mall”. So, it’s a pointless endeavor to stuff everyone into the city by making it as dense and “efficient” as possible. On the whole it costs the society more to keep it up. Instead, what you need is greater accessibility by road, by train, by bus… and move most of the people out to nearby towns and sub-urbs where they have better access to work in agriculture and industry rather than commerce and services.

        1. Plus, even the services pay people better wages when they’re not forced to operate ten pubs and five burger joints on the same street in competition.

          People should just move out of the cities, but as ironic as it is, the political parties who most claim to care about social and environmental matters also completely hate individual mobility and private transportation, and love cities full of poor voters stuck there providing them cheap services.

        2. ‘decrease population density’ – that sounds like a massive carbon cost in rebuilding the existing city and town to make it possible. And you end up covering more of the greenbelt around the cities to allow that greater spreading – not exactly a ‘green’ solution.

          A City certainly can produce stuff effectively – that concentration of people and stuff makes it possible to make stuff easily and create designs that won’t happen if all the minds and resources are spread all over. That critical density of stuff allows for much easier and quicker transport of the people and materials to the locations required.

          Also nothing forces the ‘ten pubs and five burger joints’ onto the same street in competition. The management/owners all chose to set up there, with all after the first having to expect to be in competition with each other. That is just a combination of greed and short sightedness – ‘oh existing pub is doing a roaring trade, this is a great location for a pub so lets build another right next door and get some of it for ourselves’ without thinking that the population this pub is serving doesn’t change much so just adding another and another dilutes the number of customers each will actually get.

          1. It doesn’t have to happen overnight. Once the buildings reach their technical end of life in about 40-50 years, you simply tear them down and don’t rebuild. Have a park instead.

            Low-rise dispersed infrastructure can live in between trees and greenery. If you go look at Scandinavia, most of their cities are basically like a sparse forest with houses in between trees.

            >A City certainly can produce stuff effectively

            Everything in a city is brought in from the outside. Materials, energy, food… nothing is actually made, grown or extracted, right there in the middle of the city. It’s a selling hub and a place to go to trade and consume stuff made elsewhere. Of course it produces “immaterial goods” – services – but that’s not the kind of production we’re talking about.

            >Also nothing forces the ‘ten pubs and five burger joints’ onto the same street in competition.

            Over-supply of unskilled labor and not much else to do in a city causes it to happen. Also, there is a curious effect in commerce where services such as these tend to clump up due to competition over customers.

          2. >so just adding another and another dilutes the number of customers each will actually get.

            Yet, when there are people with no jobs around and they’re looking at the situation, they go, “Hmm… I could start a pub and at least make SOME money instead of nothing.” – and they keep adding pubs until all of them are barely scraping by.

            It’s not that the people don’t know they’re splitting the customers, and it’s not “greed and short sightedness”, it’s just that they have to because there’s nothing else to do in the area than start yet another hair salon, a pub, a cafe, a boutique…

          3. > that concentration of people and stuff makes it possible to make stuff easily

            Cities were originally formed around transportation and power – a river and a mill for example. They were industrial hubs in an era when most people had only their legs for mobility, so you couldn’t source labor from very far away – a few miles at best.

            After we got automobiles, cities stopped being manufacturing hubs. The high land prices and rents, and the difficulty of logistics in a densely built area pushed all the industry OUT of the city. What remains are trades which directly benefit from the high concentration people alone, which is services and shops, banking etc.

            >create designs that won’t happen if all the minds and resources are spread all over.

            Most people can’t be engineers and planners. It’s like trying to have a business with all managers and nobody working the shop.

          4. Think about it for a second.

            Suppose you want to buy a new door to your apartment because the previous one got smashed in by burglars; there’s probably some place within walking distance where you can buy a door – but do they make doors?

            No, there’s actually a small community about 30 minutes down the highway outside of the city, where there’s a school and a church, a farm, a lumber yard, and a small factory that makes doors and windows. It’s like this for most everything you can imagine – only the sales office is in the city.

            The reason why these small communities are vanishing is because of offshoring and importing goods from elsewhere. The people in these communities move to the cities, try to get an education, and mostly fail to find jobs in the higher paying occupations because they’re either not qualified or the position is already filled, so they end up doing petty clerical work, cleaning and maintenance, or retail. Most of the jobs they do exists merely to keep the system up and sell you something, which is why the potatoes you buy at the supermarket cost you a dollar while the same potatoes at the farmer’s market cost you a dime.

            So what is the advantage of the city? Better services – at what cost?

          5. You can have a highrise filled city and still have heaps of trees – London is a commonly used example as if it wasn’t actually a city it would be according to the UN classification a forest by tree density…

            There are so so many layers to creating stuff – the city is not often built solely around prioritising the raw extraction of some material or turning it into the most basic commodities – as it makes sense to do those process near that extraction location rather ship in all the waste. Though it does happen that a city grows up around resource extraction, however what a city always ends up being is a place where all the rawer materials and simpler products are in close proximity along with a larger pool of talent for combination into the more complex, more finished product.

            Perhaps you don’t make your wooden door example in the city (though you probably do in the industrial parks and outskirts). But you equally won’t be doing the final assemblies of your more complex products out in the sticks – the production facilities that can bring together the expert welder, leather worker, carpenter, sheet metal and electronics master with a huge pile of subcontractors you can grab to do that odd job your company doesn’t need a member of staff full time for doesn’t exist outside of the city, and practically it can’t – just shipping all the raw materials to your mining town to allow for them to work at their craft only to then have to ship back through the distribution hubs (that cities tend to be) costs to much!

            Offshore production is an entirely different problem, and the stuff that is made offshore is almost always made in a a slumtastic city with lax worker protections and safety concerns by Western standards. But it is still a CITY!!

  9. Trees are no use. They can only capture as much that is part of the natural carbon cycle, and only contain it for a brief time. We have no viable method to remit and contain the fossil component of atmospheric carbon. We need to think a lot harder, and very smartly.

      1. Oh, the world will be ok. For the majority of humans however it really does depend on how fast they can adapt their behaviour and history is not totally reassuring on that topic.

    1. I agree that people don’t consider this angle, but trees are hardly “of no use”. Just spitballing here, why not harvest the trees and bury them (like a mine in reverse). That’s essentially how coal veins are formed naturally. Or maybe raise algee and then pump it down old mine shafts. Or use some method to sink biomass in the ocean (maybe do something to wood to make it heavier than salt water). After all, there was an algee on the earth on one time that would grow in the oceans and then sink to the bottom and it caused a literally ice age.

      1. If you consider just how heavily deforested the world currently is compared to historic norms you can store a great great many ton of CO2 very very long term in a forest – the biomass of a forest vs the scrubby grassland (etc) is very very heavily weighted in one direction. And yes the individual tree will eventually die, but the forest it is part of can still be thriving and so still holds all those extra ton of carbon compared to whatever is there now.

        1. If you want to sequester CO2, it’s faster to grow weeds and carbonize them by pyrolysis. You get net energy out of the deal, and the resulting biochar is a great fertilizer for farms – although most of it would just go to landfill. (see: terra preta)

          1. It is perhaps going to capture carbon faster – doesn’t mean it is going to stay captured long, there is a great potential to increase the biomass in an area but for it not to get released again the ecology you dump it in has to be able to stabilise actually holding that extra. That is where forests win, they just stick around almost on their own, have huge amounts of biomass and will keep that carbon in on its own.

    2. Personally, I turned the hot water system off in 2012, boiling the odd couple of litres when it’s too cold, whilst the sun shines. I filled the car up and parked it some time ago, and now enjoy the (physical and mental) health and wealth benefits of cycling. I grow what I can, but hopeless as a gardener.

      What are you doing/ plan to do?

        1. 10kW of solar on my roof, hybrid vehicle (I know…, but ev minivan wasn’t available at the time…), public transport to work every day now that distances are too far for biking, if I had more yard space I would plant food but hydroponics is on the cards instead.

          It’s a start…

        2. As you asked.
          Got as much solar as the roof will allow along with a battery that both trades with the grid and helps keep our power supply local.
          We grow much of our own in various types of fruit and veg (though the garden is way too small for it to be everything needed).
          Have cut down the electric consumption dramatically by finally upgrading some older electronics (and pick the more efficient option when its affordable), while also keeping electronics running as long as practical – phone has been through two battery now, laptop that I rarely need is now something like 15 years old – but it is good enough for what I need when I need it. Though I did buy a Steamdeck as a partial replacement – cheap and energy efficient gaming while supporting Valve in bringing Linux gaming to more folks, could not resist.
          Currently we don’t use the car much, though not practical to do away with entirely.
          And similar to NFM lacking more space some hydroponic ideas floating around for future projects among many other ideas that should help quality of life while reducing resource consumption in the end.

      1. Due to the recent power supply crisis, many people turned down their heating and ventilation to save energy.

        The result was that many homes are now suffering from mold infestations.

  10. “pollution deaths” is the most nebulous metric I’ve ever heard. How do you even tell if someone died of pollution related causes? Smells of made up statistics for the EU to use to punish other nation states

    1. Short of someone dying of asthma while there head is stuck in a chimney you don’t.
      But that doesn’t mean no one does die that way nor that it isn’t desirable to reduce that.

      So you look as statistics and air quality measurements. If lung cancer or asthma or something is more prevalent in areas that are high in some form of air pollution… that alone isn’t exactly proof, you know correlation does not equal causation but it is a pretty good clue worth pursuing!

    2. Friendly reminder that not being aware of a scientific field doesn’t mean it doesn’t exist or has no merit.

      In that case, epidemiology / popular health science are ~200 years old, and are all based on finding a good model, having large enough a sample, and then eliminating, through rigorous statistics, all confounding factors.

      How do you think most of the world decided to ban leaded gasoline? Scientists, in hordes, did studies on what people died on and got sick from, and eliminated common factors until with a high enough probability the right explanation was “it’s the lead!”.

      Same, by the way, for tobacco (even if looking at a smoker’s lung might be easier), a lot of flame retardants, asbestos in construction material, thalidomide, and basically *every single medical study ever run”. You do a study.

  11. Lot’s of skepticism here. That seems reasonable to me until I read what the skepticism actually is… then it’s mostly just regurgitated right-wing anti-science head-in-ass talking points.

    “One LIQUID3 bioreactor is capable of replacing one 10-year-old adult tree, or a full 200 m2 of lawn”
    Anyone have the numbers on this claim?

    “one 10-year-old adult tree”
    I thought it was young, growing trees that take in the most carbon?
    Then again, is 10 y/o “adult” for most tree species?

    1. Define “adult” in trees – if it is when they are first able to reproduce in many trees you need to add a few more decades, if it is using a human lifespan ratio quite possible need to add a century before it is “adult”, if however you just mean it looks like a tree not a stick with a few leaves 10 years might well be enough. There are also of course wild variations between tree species.

      1. All very true.

        My understanding is that the carbon capture of a tree follows a curve. Most of the carbon is captured as it grows. So a seedling might be capturing a very large amount of carbon relative to it’s own mass but it’s mass is very small so still not much. Then some years in it is big but still growing fast so it’s taking up it’s maximum amount of carbon. Finally, as it approaches it’s final size growth slows down to mostly replacing damaged parts and maybe seasonal leaves. Then it is no longer capturing much.

        Best way to use a tree for capturing CO2 might be to cut it down once growth slows, bury it somewhere that it will go a long time without rotting and plant a new tree. But then you produce CO2 moving the tree. So you need a place the tree can grow, a place it can get water without expending a lot of energy… but near a desert for burial.

        Also.. those first so many years of a seedling’s life it won’t be capturing much. Maybe a tree isn’t the best plant.

        I’m thinking fields of hemp grown along the Nile, cut and dragged off each year into the Sahara and buried there might be the best carbon sequestration scheme.

        1. Probably the best way to use a tree as carbon capture is just to use the timber in stuff that lasts and people need. Pick the right trees and you are really in good stead for long term storage in that way. And because its in use by humans it is likely to last better than dumped somewhere, even if that somewhere is good for preservation.

          Though a more natural forest will also have many many tonnes of very enduring and ecologically useful deadwood and can always gain soil depth, just because the tree died doesn’t meant everything it ever captured gets released quickly if at all. Lots of carbon can stay captured in the various types of soil and rock, and it stays there until we go and change the local ecology.

          Not sure hemp dumped in a desert is a good plan – I think it will probably just turn to dust and get back into the carbon cycle very quickly – hemp is a great material though, can be used in many long lasting situations or as a replacement for many short lived but very definitely carbon negative and quite possibly ecological vandalism parts if there is the will for it. The 6 pack beer can stacking plastic bits for instance could perhaps be replaced by a few winds of a coarse hemp fibre cord – obviously there is a cost upfront in making that change, and the required volume of cordage with folks beer and soft drink love might just be too great to make it practical. But on the ecological soundness front and the carbon in the atmosphere reduction front it is probably a winner in very short order, and one that might actually be practically possible being a minor change in lifestyle and economic activity.

  12. there is no way in hell that this thing works. having worked myself with micro-algae during my bachelor thesis i can tell you that besides the obvious stupidity of the co2 and air cleaning facts those things are almost impossible to keep “clean” meaning they are very prone to bacterial infection. also micro algae unlike plants and bacteria are almost impossible to genetically engineer. and lastly they usually tend grow extremely slowly or even to starve to death and get yellow to brown if you don’t give them a nice and juicy buffered growth medium full of nitrogen protein and sugar. so yeah you can use them as fertilizer later on but all the nitrogen you get is the nitrogen you put in to grow them in the first place they don’t fix nitrogen from the air.

    1. No personal experience but I know of many studies that have really been praising how hard it is to go wrong growing some specific algaes – maybe the ones you were worked with are really really tricky, but it seems that is not universal. Requiring the right growing medium wouldn’t be anything new, so there you could be entirely correct. Though I’d not be so certain there is no nitrogen capture going on – lots of polluted air bubbling through a wet chemical soup, almost certainly going to be some interactions going on that could end up as a capture.

      Also for this use case do you care if it gets infected by something else anyway? The primary point seems to be cleaning the air which just bubbling the air through water would do at least to some extent. And you have to go around cleaning and harvesting it too.

      1. arguably you are right some species may be more adapted and resilient that the strain we used back in the day but usually those are the one growing in brine where they can out compete almost all other microorganisms. however working with brine poses some challenge on its own. as far as i know micro algae don’t fix nitrogen and the tiny amount of dissolved nitrogen in the solution is not biologically available to them. or you mean some sort of interaction with the growing medium itself? without knowing the details of what they are using i cant really comment on that but seems unlikely.

        from an “air cleaning” perspective no i don’t care whats growing in there might as well be plain water and green dye for aesthetics reason for all i care but if you start to talk about carbon capture heck yeah you should care …. no algae no photosysnthesis => no photosysnthesis no co2 capture. as simple as that

        1. >no photosysnthesis no co2 capture

          Agreed, mostly anyway – some might well get dissolved and react with other crap in the algae tank’s water so it sticks around. But as you have to go round cleaning them and harvesting them all the time a little period when the algae is not very healthy or dead inbetween doesn’t change much – just means the system is operating at lower efficiency than it could, but it is still capturing just fine for much of the time.

          >as far as i know micro algae don’t fix nitrogen and the tiny amount of dissolved nitrogen in the solution is not biologically available to them. or you mean some sort of interaction with the growing medium itself?

          Yeah I don’t know about a fixing nitrogen species (wouldn’t surprise me though), but with the amount of stuff in a cities air I would expect it is filtering out ammonia and nitros oxides that will then react at times with something else in the wild mix of stuff there to stay stuck in the algae tank and may well become bio available to the algae. There is just too much stuff particulate and gaseous in a cities air to really even make good guesses as to all the chemistry that will be going on.

  13. They look pretty bright, and use energy for other things too like USB and water circulation etc. 24/7. So I wonder if these things use way more energy they get from the solar panels, especially over winter. In which case they will be using grid power, hence costing some CO2, I hope it still offsets its own CO2 usage!

  14. >Historically, nature has used trees to turn carbon dioxide back into oxygen for use by living creatures

    Trees evolved something like 350 million years ago, photosynthetic microbes are estimated to have existed about 3.4 billion years ago, so trees are the young upstarts really. Estimates seem to vary wildly, but 20-50%+ of current oxygen production is from the oceans, rather than terrestrial trees.

  15. These tanks won’t last 2 weeks in major US cities. Within days, there will be scratched all over. Eventually broken into pieces by maniacs using whatever they have on hand. The mess will also make the bench unusable.

    1. I actually seen one of those first hand. still there after almost a year. sort of clean, no vandalism on it. Though in summer it was overgrown to the point of being no longer transparent.
      On another hand – Belgrade has surprising amount of trees in many areas. and without them – summer would not be tolerable here.

      As for vandalism – do not see it as big problem here. Grafiti – yes, but serious vandalism – no.

  16. Wait… An included electric light is the source of photosynthesis… Do you mean the energy source for the CO2 capture comes from CO2 emitting sources? When the capture mecanism is freaking photosynthesis? And it’s not an april’s fool, really ? Shame on you hackaday for this arty greenwashing BS. What kind of second Law breaking rubish is that…

    1. I know ithas a dedicated Solar panel. That’s irrelevant: electricity production is still massively CO2 emitting overall. The Solar panel could be (and should be) used to power something else.

  17. And now for some liquid tree solar highways and sidewalks: sure there is a good potential for milking those green-washed dückheads in Brussels, Haag or Berlin.
    Seriously, HaD: Why this BS?!

  18. This is like trying to fight a tornado by throwing pebbles at it. One fancy air purifier isn’t going to make any difference, when practically every city here in Serbia has sky high pollution rates. What we should really do is start phasing out coal power plants and instead turn to gas as a primary source of energy, since that’s our only viable option at the moment. But unfortunately, the Serbian government is way too corrupt and inexperienced to start any sort of useful project, like the one mentioned above. All they care about is making a profit for themselves and their investor friends. This leaves people prone to serious illnesses, and increases the rate at which the climate change is progressing forward.

  19. It is an art piece, but no practical solution.

    If you want to have a forest in the city quickly, then I would propose bamboo planted in steel containers which are manageable by forklift. Can be produced locally, can have seating, too, evaporates water, and sucks up as much CO₂ as biomass is built up. also resistant to electricity glitches.

    Or better yet, those “bicycle stand trees” where bicycles and scooters are pulled up in the “crown”, which can also have a seating bank, carry street lighting, have a cap of creeper plants
    for example or or something like this.

    further ideas:
    in heat waves these could spray cooling mist
    every N-th “tree” could have a proper unisex toilet, if the tree is placed over existing sewers.
    every other N-th “tree” could be a package storage box system instead of a bicycle storage system
    Streets could have a theme, if the “trees” carry fragrant plants, like thyme, lavender, Brugmansia (…poisonous…)

    Needs a visit once a week, watering, emptying the waste baskets, check the lanterns, remove grafiti, pressure wash the pavement below.

  20. >two neighbouring coal power stations
    Which I imagine is where they draw the power from for the lights/phone charger as I doubt a small solar panel is enough to keep it lit that bright all night long

    1. Looks like the size of the panel(s) on the top will lead to a rating somewhere in the 300-1000 watt peak power range to me – so one hour of decent sun will be enough for many hours of power to its own LED, and even a pretty dark gloomy day probably catches enough to run that light all night reliably. Might not be the best use of the solar panel to do that, so I’d hope it was tied to the grid or powering a wider array of street lighting or something so the solar performance isn’t so much more than the thing needs for itself.

  21. I think that much of what is criticized about these liquid trees could simply be solved by making them with reused materials and sacrificing aesthetics.
    Maybe a cylinder without plexiglass, a small wind turbine, and a sign that says: “this helps you breathe easier.”

    Greetings from Argentina.

  22. Bamboo!

    That’s the answer. Grows like a weed, takes in atmospheric CO2 and can be used for industrial wood purposes when ready. Where we can we need to grow bamboo!

  23. The HAD comment brain trust has spoken, and it’s in line with the present day religious doctrine.

    – Don’t build ANYTHING.
    – Just club each other over the head while chanting “Gretaaaaaa…. Gretaaaaaa….”, interspersed with “the end is nigh! repent all ye sinners”.
    – Don’t eat meat.
    – Don’t eat most veggies either. In fact, don’t eat at all.
    – Don’t use fossil fuels.
    – Don’t use nuclear.
    – Don’t build wind farms.
    – Don’t build solar.
    – Eat the rich.
    – Remember, rich is relative. So you will not want for sustenance until you yourself are eaten.
    – Eventually almost everybody would be eaten, and the lone survivor would also be gone. Then, nature can begin healing.

  24. The author mentions deaths from pollution, however carbon dioxide isn’t inherently toxic unless you suffocate in it. The deaths caused by pollution are from other pollutants such as particulates, which these devices don’t seem to filter out

  25. The solar panel IS used to power something else. From the article, these solar algae bench thingies also have USB charging ports. It’s probably not economical to make a grid connection for the handful of watt-hours of excess energy these thing produce. I think a wifi hotspot would be a nice addition though!

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