Metabolizer - A recycling center powered by trash!

A deployable power plant that eats trash and turns it into energy, electricity, fuel, and eventually very nearly anything else.

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The Metabolizer is a prototype for a low-cost, easily-replicable waste processing system that is powered by the trash it consumes.

It's called the Metabolizer, because it is intended to have the same basic metabolism as a living organism- capable of decomposing common waste materials in order to power itself, and fabricating as many of it's parts as possible from recycled waste materials- enabling it to grow, evolve, adapt, and eventually self-replicate, like a living organism that eats trash.

The prototype on this page can't do all that yet, but it CAN:
-Shred wastes into small bits, using energy derived from waste
-3D print large plastic objects directly from plastic flakes
-Make bio-char and sequester CO2 from the atmosphere
-Generate a clean gas that can run gas engines and appliances
-Generate 120V/60Hz electricity
-You can build one out of readily available parts, with minimal specialized tools or skills, for around $2,500, or less.

Problem Statement:

Unlike all healthy living ecosystems, which can regenerate "wastes" back into living things in an infinite loop powered by sunshine, modern human systems increasingly tend to pile up wastes faster than the biosphere can break them down again. Waste plastics are a particularly problematic example of this paradigm of consumption, because very few living organisms exist that can break plastics down, and none exist that can do it as fast as we're producing them. 

Yet, however dire our current situation may be, it is not unprecedented in Earth's history. 360 million years ago, plants suddenly evolved the ability to synthesize Lignin- which was up until that point the most complex organic compound that had ever been synthesized on Earth. For 60 million years (!!!) trees grew, died, fell over, and we're buried, but the solar energy trapped in their chemical bonds was never broken down and released- because no fungi or bacteria existed at that time that could break down woody biomass. That's where most of the worlds coal came from. It wasn't until white-rot fungi evolved specialized enzymes that wood became the 100% compostable component of living systems that we know it as today.

Plastics are mostly made of the same stuff that wood is, and they are extraordinarily energy-dense. A gallon of plastic has roughly the same energy content as a gallon of diesel fuel. So whether or not humans survive the Anthropocene, we'd be flattering ourselves to believe that we could end ALL life on Earth, and that means that eventually SOME living organism will almost certainly evolve a metabolic pathway that can convert the nutrients and solar energy locked up in the plastics in our oceans and landfills, and use those resources and energy to synthesize the physical structures that allow them to continue to live, grow, and self-replicate. It's only natural! It's what life does. 

But why should we wait for humans to go extinct? We built the systems that made the plastic, we can build systems that break them down. We can designs systems that can break down our wastes and use the energy and material in them to meet human needs, for things like food, water, shelter, energy, and information.  We can create human-made systems that integrate with the local ecology, that behave as living organisms do, that resolve the conflict between modern human society and the rest of the biosphere. Don't believe me? Great! That's what makes this project interesting! 

Check it out:

It's possible to use plastic and biomass to make a flammable gas that can power internal combustion engines.

It's possible to use internal combustion engines to do things like shred waste and make electricity. 

It's possible to thermally decompose many common plastics into liquid fuels that can run unmodified gas and diesel engines.

It's possible to use electricity and and shredded plastics to 3D print or mill plastic objects in very nearly any shape (that's why it's called plastic)


The Design Challenge:

This project is my best attempt to design a machine that mimics the metabolism of a living organism, that meets or strives to meet the following criteria:

1) Is capable of metabolizing as many common household waste materials (cardboard, paper, plastic, glass, aluminum, etc, etc, etc) as possible into the resources and energy required to power itself as long as there is trash or biomass available to eat.

2) That is capable of synthesizing and replicating ALL of it's own parts, enabling it to grow, adapt, evolve, and self-replicate. Similar to the Rep-Rap project, the goal would be to build a machine that fabricate all parts of itself.

3) That is open-source, well-documented, and designed for easy replication, using parts that can EITHER be fabricated using common CNC tools...

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Seize The Memes Of Production!

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  • 1 × |.........................................[THE HEARTH]...................................| The following components are required to build the Hearth, which is the reactor and distillation tower, and the base for the Turbine. See Instructions Section for Build Notes
  • 1 × Lava-style Patio Heater Est cost new: $220. The metabolizer is a distillation tower, and you need some kind of support to hold the tower vertical. Patio heaters are readily available used or free, and aren't prohibitively expensive, even new. They provide a sturdy, good-looking structure to hold the rest of the distillation tower in place. I found mine for $10 at a goodwill outlet bc the glass tube was missing. Check craigslist! For reference:
  • 2 × 1/2" Brass Nipple
  • 1 × 1.5" Tri-Clamp -2" Concentric Reducer
  • 2 × NPT Brass 1/2" Tee

View all 74 components

  • First successful multi-layer print!

    Sam Smith03/05/2019 at 18:41 0 comments

    I spent last night dialing settings for the 3D printer, and was finally able to extrude my first multi-layer object. There's still a lot of improvements to be made, but this is a huge step forward! The final part is light and flexible, and so strong you can't pull it apart or break it no matter how hard you try. 

    This was made with #5 polypropylene plastic, which used to be trash food containers, which were washed and shredded with the Precious Plastic shredder into fine flakes, and then fed directly into the print head.

    The next step is to see what kind of low-resolution objects I can make with this. I'm also interested in trying to make a part with 100% infill to see how solid an object I can make. Stay tuned!

  • And isn't it Holonic? (Don't'cha think?)

    Sam Smith10/22/2018 at 13:49 0 comments

    The metabolizer is made up of at least 7 distinct sub-systems- the Hearth, the Turbine, The Shredder, The Printer, the Gasometer, and the Generator. Like the organs in your body, and the cells inside the organs in your body, and the organelles inside the cells inside your body, the individual machines that make up the metabolizer all have unique chemical roles to play, and while they can each be considered as distinct systems, they are also dependent on the other machines in the system in order to complete the metabolic process, and so they can also be considered as part of a larger system.

    All living things are best described as processes rather than things- life is, by definition, a thing that is constantly happening. And all lifeforms, even the simplest ones we know of, can be described in terms of their sub-systems, things like hearts and cells and mitochondria, and those things can also generally be described in terms of their sub-systems, like ventricles and organelles, and all of those things can all be described in terms of what they take in and what they put out- they are all processes. This may seem kind of obvious, but it’s an important distinction to make, because our language categorizes most of these things as 'nouns', when really they are verbs.

    This concept of things as processes nested within larger processes, is called a “holon".  A holon is any thing that can be accurately described as BOTH an individual thing, like a heart, AND also as a component of some larger whole, like a human. A lot of people that I talk to have never heard the term ‘Holon’, but when I tell them what it means, they often have an immediate recognition of the concept. Anyone who’s spent any time looking around this world knows that nature functions in this way, even if we don’t have widely-used words to describe it (yet).

    When we're trying to talk about complex systems, it’s important that we make this distinction, because it’s a fundamental part of of how complex systems work. Some things are things that are actually things, like a pile of rocks, or a gallon of water, and some things are better described as processes within a system, like an engine, or a human. A generator and a human can both be described in terms of how much fuel they consume, how much O2 they inhale, how much CO2 and H20 they exhale, and how much work they produce. 

    This is not very different from what the Mitochondria in your body are doing (that is- the cells inside your cells inside your organs inside your body). Mitchondria play a pretty specific chemical role- as we all learned in high school, “The mitochondria is the powerhouse of the cell”. Mitochondria take in a complex hydrocarbon- in this case glucose (C6H12O6), and react it with Oxygen to produce CO2, H20, and energy, stored in a highly refined, and easy to access from- ATP.

    Chemically speaking, there’s no fundamental difference between what a Mitochondrion does in a cell, and what the metabolizer does in my backyard- it takes in complex hydrocarbons, like sugar or polyethylene, and breaks them down by reacting them with Oxygen from the air to create H2O, CO2, and a refined, readily available form of energy. In cells, that refined energy is ATP. ATP is Adenosine Tri-Phosphate- it’s a simple molecule with a 3-phosphorus “tail”. Breaking the third phosphorus molecule off this tails is easy to do and releases a relatively large amount of energy. ATP is the energy that powers all of the chemical processes inside the cell. In the Metabolizer, electricity plays the same role as ATP does in a cell- it’s a highly refined and readily available form of energy that can easily and efficiently power the rest of the system.

    In both cases, the energy released from those hydrocarbon bonds is ultimately solar power. All life on Earth, with fascinating but negligible exceptions, is powered by sunlight in one form or another- wind, rain, sun, food, biomass, and fossil...

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  • Don't hate me for going electric.

    Sam Smith10/21/2018 at 00:17 0 comments

    Just had a major "EUREKA!" moment! CLEAN PORTABLE 120V/60HZ POWER ON DEMAND FROM TRASH GAS! One thing that's been bugging me as the deadline for the Hackaday Prize approaches is that the reactor part of the system is very simple to build and requires almost no specialized skills- not even welding or cutting. It can be built entirely out of readily available parts that you can get on Amazon or at any hardware store (detailed BOM coming soon). I did that on purpose, because I wanted this project to be as easy to replicate as possible. But the engine/shredder/generator I built, while a neat proof-of-concept and technically what I had hoped to build, is super-janky, highly technical, and would be very difficult for others to replicate since it's all custom parts and custom attachments.

    Powering the shredder with electricity is much easier to do than direct engine power, and it lets you easily reverse the motor if it gets jammed. It may not be quite as powerful or efficient as direct engine power, but the gains don't really make up for the added difficulty to build. It's also WAY quieter, which is important if you want to be able to actually talk to people.

    So as a last experiment before the deadline, I took a chance and bought a Harbor Freight "Predator" generator for $550 (including the 1-year unconditional replacement policy, of course) to see if I could get it to run on trash gas. I took off the side access panel, and the cover to the air filter, and removed the foam filter that came with it and replaced it with another piece of foam I had- so I could put it all back together and return it if it didn't work.

    I copied the shape of the air filter cover, and used my girlfriend's Glowforge to cut out the parts in clear and black acrylic. The Glowforge has a "trace" function that makes making simple parts like this super easy- no CAD! I had to play around with the air-fuel mixture, and promptly ran out of gas (you can see the barrel emptying in the vid), but I was able to get it to run with enough speed to produce clean, 120V/60Hz house power, which is huge! 

    While there is still a lot of testing to do (total wattage output, long term wear...) this a major step forward! This means that even if you bought all of the parts of the system new on Amazon Prime, which is the most expensive way you could do it, it would all still come in at under $2000 for everything (not including the Shredder ($600-$1200) or 3D printer (>$500)), and it would let you produce around a kilowatt of clean AC power from any reasonably dry biomass- woodchips, pellets, grass clippings, dog poo, cardboard, paper, even the Amazon packaging all the parts came in... AND it produces hot water in the process!

  • Come on zeolite my fire

    Sam Smith10/19/2018 at 23:06 1 comment

    The Metabolizer doesn't require perfectly dry material to make fuel, and in fact I've run it with some pretty seriously wet woodchips, with no problem. However, being able to remove all of the water from incoming material before it enters the reactor to be thermally decomposed would have several distinct benefits. 

    First of all, if you know the material is completely dry, you get a better sense of how much actual biomass you're loading in by weight, which lets you figure out how much energy you put in, versus how much energy you get out, and that lets you calculate the overall efficiency of your system. 

    Second of all, it ensures that the liquids that distill out aren't watered down, which means there is less refining to do, and less liquid to deal with.

    Third of all, if you could remove the water in such a way that you were able to recover it, then the system would actually produce clean water, would be super neat since humans need water to live. 

    So I've been looking into ways to dry out the material before it goes into the metabolizer, that isn't too insanely energy intensive. A simple dehumidifier inside a closed container is remarkably viable considering you get quite a lot of very-nearly-drinkable water out, but it's still a bit too power hungry for my liking, and it requires an extra bit of specialized equipment that is prone to breaking.

    So the most intriguing option I've found is using desiccants, specifically, "zeolite" desiccants, which are a particularly fascinating material and so I wanted to do a log about them.

    Zeolites are a class of naturally-occurring alumino-silicate clays (although man-made zeolites also exist), that just happens to have a particular molecular structure that gives them some very interesting properties.

    Zeolite means "Boiling Stone" in Latin, because when zeolite is heated to around 300-600F (depending on the type) it expels a large amount of steam- seemingly from nowhere. The reason this happens is that the crystalline structure of Zeolite acts sort of like a cage for water molecules. Water molecules are attracted by the inter-molecular forces inside the zeolites, and at room temperature water molecules migrate into the crystal matrix and just kinda get stuck there. This is called "adsorption".

    There are over 50 types of zeolites, but the kind I'm looking at, 3A (which refers to their pore size- 3 angstroms across), can adsorb roughly 20% of their dry weight in water. For this reason, they are often used in industry as desiccants. They're also widely used in chemistry as "molecular sieves" since only very simple, very small molecules can enter (and get stuck in) their crystal matrix, and everything else just passes between the pellets. So they're often used to selectively remove gases such as water vapor, hydrogen sulfide, and carbon dioxide from gas streams. 

    Zeolites will absorb water from air until they are saturated- and all you have to do put them in the same air-tight container with a wet material, and they will suck the moisture out of the material. Once they are saturated, they can be completely regenerated by heating them up to their recovery temperature. The heat causes the crystal lattice to expand, which eventually allows adsorbed water to escape (which is almost pure water, and easy to capture and condense).

    But the most intriguing part of this thermodynamic cycle (to me, currently) is that it acts as a near-infinitely regenerative heat battery. When you heat up zeolites to their recovery temperature (which is on the lower end of the same ball park as the pyrolysis temperature of biomass- temps the metabolizer can easily reach) they start releasing water vapor, and that takes energy away from the system- it's an endothermic reaction. You have to keep adding heat to the system, but it won't get any hotter until all the water is released. You spend heat energy in order to recover the zeolite, and that makes it more efficient than using a vapor-compression...

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  • The answers are blowin' in the wind

    Sam Smith10/18/2018 at 18:23 0 comments

    I decided to re-design the turbine at the last minute, since the parametric design was a little too complicated to do on the timeline I need to do it in. I still want to try it out, but it'll have to wait for later. But in the process of designing something light and cheap and easy to make, I hit on a much simpler, and apparently effective design! 

    This design only uses a single sheet of coroplast- around $12 in material. I twisted the parts in sketchup, and then made cross-sections for the top and bottom, and cut out the parts on my partner's Glowforge (she makes laser-cut jewelry for a living). 

    I had originally thought that I would sort of sew the top and bottom plate together with wire, but that ended up being pretty tedious, and after play around with the parts a bit, also turned out to be unnecessary. I ended up not using the bottom plate at all, and just used the slotted one. The cuts are accurate enough, and the coroplast is flexible enough, that I could just slide the turbine vanes through the slots, and they would stay press-fit in there.

    This had not been my intention, but what ended up happening is that since the coroplast vanes are twisted and under slight tension, when you align them in a circular array, they end up creating a sort of reciprocal "tensegrity" effect, where they are all pushing out against each other, which makes the turbine remarkably strong and sturdy for it's weight (less than 1lb). I dropped it from about 7 feet twice by accident while figuring out how to mount it, and it was fine- it just kind of bounced.

    I used a gear I had laser cut for a failed prototype earlier in the project, and wedged it into the top of the center tube. This was an inelegant hack, but worked surprisingly well. I'm using a NEMA17 stepper motor as the central bearing- since I need a bearing anyway, and the stepper will produce a bit of power. The neat part about doing it this way is that the power is produced on the rotating part of the turbine, not on the fixed pole.  

    This lets me hook the stepper motor up to some copper "fairy light" style LED strings, and wrap them around the turbine. When the turbine spins fast enough, the LEDs light up and strobe directly from the low-voltage AC power produced by the stepper- visualizing power output with light. The RPMs required for this to happen are still higher than I would like, but it does happen, and that also makes it kind of special, like an achievement to be unlocked. 

    I'm hoping that when the gas mantles are on (did I mention I got the gas mantles running on trash-gas), the hot air will push out the top of the lamp and out through the lower vanes, causing the turbine to spin- eventually fast enough to light up the LEDs. If that works, then the effect will be that as the Metabolizer heats up and starts producing gas, the gas mantles will start to glow brighter and brighter, the turbine will start to spin, and then the lights on the turbine will begin to fade on, a swirl of strobing points of light that get brighter as the turbine spins faster- hopefully to dramatic effect...

  • What is plastic? (It maybe won't hurt me, won't hurt me- I know more...)

    Sam Smith10/13/2018 at 20:13 0 comments

    In the process of learning how to recycle plastic, I've learned a TON about what plastic actually is, how it's made, what it's made of, and why the different types have the particular (sometimes peculiar) properties that they do. 

    It's not only fascinating, it's really empowering! For my whole life, plastic has been a material that I have had zero control over. I couldn't make it, I couldn't work with it, and I didn't get to decide what gets made out of it. When I started this journey, basically all I knew about plastic was what most people "know" about plastic:

    1) It's made out of oil, and oil is both running out AND killing the world, and you should feel bad about that.

    2) It can't be burned, and if it is, it produces a poisonous smoke, and you should feel bad about that.

    3) It doesn't decompose, EVER, and it's piling up in the oceans and killing the world, and you should feel bad about that.

    4) It's everywhere, it's in everything, and is extremely difficult not to use, and you should feel bad about that. Especially straws. 

    5) It's made out of toxic chemicals and is probably leaching poison into our water bottle right now, and you should feel bad about that, and probably buy a new water bottle.

    Our society's relationship with plastic sums up the feeling I get from our entire industrial economy- Nebulously terrifying, clearly unsustainable, manufactured by a corporate system that is entirely outside of my control, but also still definitely MY FAULT for the fact that it's killing the world.

    It's a lot easier to be afraid of things we don't understand, and most people don't really understand plastic. That's why I think the term "Precious Plastic" is so brilliant. In two words it reframes our assumptions about plastic, and refers to it as the precious, abundant, disruptively useful meta-material that it really is.

    And of course, all that being said, plastic CAN INDEED be toxic and dangerous. But that's exactly why understanding how, why, and when plastic is toxic is so important- because plastic is far more benign that people often think that it is. When you understand a material, it empowers you to be reasonably cautious about it and to take appropriate safety measures, instead of just being generally afraid of it. Fire is dangerously hot, but it's really, really easy to take the proper precautions to have a fire and not burn yourself. Plastic is the same way. It can be dangerous, but it's fairly easy to avoid danger if you know what to look out for. 

    SO! This post is going go over all the very-specific ways plastics can be dangerous, so you can take reasonable precautions. It's is accurate to the best of my knowledge, but the best of my knowledge is constantly changing- so revisions, additions, and factual corrections are always welcome. Now, let's revisit over those 5 things people "know" about plastic that I mentioned earlier..

    1) Plastic is made out of oil, and oil is both running out AND killing the world, and you should feel bad about that.

    So to address this, let's start with something a little more basic- what even is plastic? There are many different types of plastics, and they all have different chemical and physical properties. However, all plastics are polymers, which just means that they are long, repeating molecular chains of a base-molecule, called a monomer. Poly-ethylene, for example, is just a long repeating chain (polymer) of the ethylene monomer.

    But where did that ethylene come from in the first place? Most people know that most plastics are made from oil, but are a little sketchy on exactly how. So here's a quick recap- crude oil is ancient organic material, mostly plants (basically fossilized sunshine), that were not fully decomposed by animals, fungi, and bacteria before being buried deep underground by sedimentation and/or plate tectonics, which cooked the material under heat and pressure in such a way that the organic molecules...

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  • [maniacal laughter] (cont'd)

    Sam Smith10/09/2018 at 15:59 0 comments

    Nathaniel and I met up at CTRL+H last night and hacked on the printer for nearly 5 hours. We successfully "printed" our first "objects" directly from shredded trash flakes, and we learned a lot in the process. One of the most promising things we learned is that coroplast sheet can indeed be used as a build plate. For a printer of this size, making a heated bed like a typical printer has is a daunting and expensive design challenge. But without a heated bed, how do you get your first layer to stick? 

    I knew that Polypropylene is very self-adhesive, and my hunch/hope was that maybe I could just lay down a sheet of cheap Polypropylene coroplast and that the molten PP would adhere to that, because they're the same material. That way you could just slide in a piece every time you print, and then cut off your object (and then shred up the scrap and print with it, of course). That part worked out quite well- the PP adhered much more strongly to the coroplast than it did to the wood underneath. That means that a heated bed upgrade isn't necessary- putting the cost to replicate this setup at under $500, using almost entirely 3D printable, laser cuttable, or widely available parts.

    We decided to try and print out the Hackaday logo [based on this model from Thingiverse], and this the result of our first attempt. It's more of an "ckaday" logo, but it was an encouraging first shot. Nathaniel adjusted the ratio of extrusion to speed, and we tried again. One of the challenges of this kind of printing is that the extrusion is non-linear. It's not moving a spool of solid filament, it's building forward pressure in the extrusion barrel, and so there's a 3-5 second delay between when the auger starts pushing and when the plastic actually starts coming out of the nozzle. Luckily Nathaniel speaks robot quite fluently, and after a bit of arguing, we got this:

    Not bad! Not, you know, great either, but pretty damn good for our second try. Next steps are to rebuild the extruder to be little sturdier (it was wobbling back and forth a little when extruding), mount the thermistors more securely (one of them got pinched and wouldn't read) and build an actual wiring harness and material feed. But all in all, I'm really happy with this test, and I am confident that this approach can produce useful (if not-very-detailed) objects.


  • Start your engines!

    Sam Smith10/08/2018 at 18:32 0 comments

    I had intended to just fire up the new setup to test to make sure my seals and connections weren't leaking (or if they are, where), and it ended up working so well I was able to fire up the engine! Still a very basic test, with no intermediate gas storage, but very promising!

    The last major step to demonstrating a working prototype is connecting the engine to the gear box, and the gear box to the shredder! From there, there are a million upgrades and re-builds I still want to do, but I'm trying to focus on getting a tangible proof-of-concept running in time for the Hackaday Prize deadline! Onward!

  • Throwback Thursday

    Sam Smith10/04/2018 at 17:09 0 comments

    I've been doing these logs sequentially, but today I wanted to do a throwback to highlight some work we did back in February, right before I pitched the Metabolizer to Hackaday in the Open Hardware Challenge. This project has been a huge learning process for me- lot of parts of it are right outside my skillset. 

    I'm a designer/inventor by nature, the kind of person who needs to understand how things work. So I'm really good at understanding what's possible with currently-available tech, but I rarely have the actual technical skills required to make it happen. 

    Luckily, I have very talented friends, who have helped me immensely on this project, and since I can't pay them anything for their help I want to make sure I at least give them proper credit!

    These are my friends Darcy (Hackaday user DRC3P0) and Matty (Hackaday user softjitter) assembling the MPCNC. Darcy works at the FabLab at Portland Community College, and so she help me print all the parts required to build the MPCNC, and Matty helped us get it moving. They are both rad and very accomplished makers, and you should check out their work!

    I had never worked with any kind of CNC machine before, although I've been aware of them and had friends with access to them for years. Without Darcy and Matty's help, I wouldn't have known where to start!

    Here's a funny picture of Darcy. Sorry Darcy. You're great.

  • It's parametric! (cont'd)

    Sam Smith10/03/2018 at 18:11 0 comments

    Dallas and I hacked on this parametric wind turbine design again last night, and made some real progress! The model now auto-generates flattened array of individual layers, and adds number tags, so they can be turned into individual cut-files required for CNC fabrication. I really want to make a turbine that is as tall as the patio heater is (I'm a sucker for symmetry, I'll admit). That's about 7 feet, or 84 inches. At 5 layers per inch, that's 420 layers of 4mm (3/16") coroplast. By my estimates, that would require around 20 sheets of coroplast, which go for about $11/sheet. So a couple hundred dollars, if using virgin material. But coroplast is also easy to find in the waste stream in the form of lawn signs (and there will be lots available come November 6th...) So if I can "recover" a few of those, that should bring down the cost significantly.

    This is my most-current design on Shape diver. You can play around with it too! Check out the live parametric model here! Unfortunately, shapediver doesn't let you download the file, or the cut-files, which would be really epic, but it does at least give you a taste of the power of parametric design, without all the expensive hardware and difficult to learn software. And I'm uploading the Grasshopper definition file to the Files section, so even if you don't have Rhino/Grasshopper yourself, you can find the parameters you like on shape diver, and then send the values and the open .gh file to someone who does, and they can compile the cut-files for you. And of course I will also post the cut files for the version I end up building either way.

    But I really like the idea of letting people play around with the parameters of this design. This will not be an efficient wind turbine, and efficiency is not my top priority at this point. But I think it's cool that people could tweak the design to suit their preferences and then test their results against mine, and together we could find more-and-more efficient versions moving forward. It's sort of a microcosm of how I hope this whole project could be improved systematically over time by a community of folks, like the Precious Plastic machines have been. 

    But if that's gonna happen, I've got a lot to do in the next 3 weeks!


View all 34 project logs

  • 1
    Building the Hearth

    The words 'heart' and 'hearth' share the same root. The hearth is the heart of the Metabolizer. It's primary sub-systems are a reactor, a reaction vessel, a distillation tower, and a support structure.

    The Support Structure:

    The support structure I used is a 7' tall "lava" style patio heater. Patio heaters with glass tubes like these break fairly often, and people often don't want to fix them, and so they are easy to find used for cheap or free. I got mine at a goodwill outlet for $15. You don't need to use a patio heater like this, but you do need something sturdy to hold the distillation column in place securely, and this works kinda perfectly. All you have to do is remove the propane regulator, catalytic burner assembly.

    The Distillation Column:

    The purpose of the distillation column is to cool and refine the hot gasses as they escape from inside of the keg and it heats up. The distillation tower needs to make a secure, but pressure-releasable seal to the top of the keg, and it needs to cool the gas flowing through it. 

    There are lots of ways to do that- copper tubing, CSST gas tubing, but I ended up using Tri-Clamp fittings because they are easily available (they are commonly used for homebrewing) and because they are highly modular and easy to reconfigure and prototype with. It's like playing with legos.

    I used both TC2" and TC1.5" fittings in my build, but in retrospect, I wish I'd just gone TC1.5" for the whole tower. The 1.5" parts are cheaper, and you can fit more distillation stages in the same space. TC 1.5" ferrules also make a perfect seal with the neck of a Sanke keg, so it just makes sense to make the whole tower 1.5" fittings. 

    I have some alternative AliExpress links in the "Hearth" tab of the BOM spreadsheet in the Files Section. You could fit in 4 condenser cups instead of the 2 I have now, which would mean more control over the fractional distillation process, and potentially the ability to select for higher-grade fuels. More testing is needed here.

    When I fire a keg, I pack a bit of wet sand around the neck of the keg and the tower base, and between that and the weight of the tower resting on the keg, that makes it gas tight. When I'm done firing and want to unload a keg, I can pull down on the pulley line, and it lifts the column up and off the keg, and can be locked in that position, so that you can easily unload the spent keg and load a new one.

    The Keg

    I am using 1/6th Barrel Style Sanke Kegs as "fuel cartridges". These can be bought new for around $100, but are also commonly available used/free. Check craigslist. I got like 4 just by asking my friends on facebook. The more you have, the better. You can fill them up with shredded burnable fuel material, dry them, fire them, cool them down, clean them out, and then refill them...

    The Keg simply acts as a relatively high-temperature resistant reaction vessel, that can contain the hot biomass without letting any air in. I'm using them because they're widely available, and can handle temperatures higher than biomass needs to be to pyrolize.

    The Reactor

    Is actually just a nearly-unmodified Char-Broil Turkey fryer. They cost $100 or so new, but can often be found used. I got mine for $5. It works well because it keeps the heat contained and directed without adding much weight, it allows you to heat kegs with an outter ring of charcoal, and it also has a built in propane gas burner, which can can be used to start charcoal with propane, or to feed syngas back into the reaction chamber once the reaction is going. In bio-char making, this is called "retorting"- and if you don't want to store the gas, you can simply retort it and make biochar from woodchips.

    You don't need to use a turkey fryer for this, but I had one and it works fairly well. Primary desing concerns are that you need to keep the reactor hot, you need to be able to set the keg securely in the center, and you need to be able to apply heat effectively from the bottom. I could imagine lots of other ways to do this, so maybe just use what you have! I was also experimenting with using a full-size keg as a reactor, which might work but needs more experimenting.

    The Connectors

    I used standard 1/2" appliance hoses for the water lines, and 1/4" compression fittings and copper tubing for the distillation cup lines. If you don't want to deal with capturing and storing liquid hydrocarbons, you can simply not use the distillation cups, or cap them, and that will cause the tars to flow back into the reactor and break apart into smaller molecules. The way you do the connectors will depend on what kind of TC fittings you get. I used brass tees with 1/2" copper adapters in order to spiral the tubing around the center column.

  • 2
    Building the Printer

    The best instructions for building the MPCNC are available at I will not try to improve on their documentation, because I can't. I will make the following notes about what we learned during our build, though.

    1. We printed the 1"/25.4mm version of the MPCNC parts, which lets you use exactly 1" OD tubing. If you want to use conduit, you have to make sure you print the right size parts. 3/4" EMT conduit is something like .94" OD, and so we had to use 1" aluminum tubing instead, which increased the cost a little.

    2. Wire the steppers in parallel! I bought the parallel wiring kit from V1 engineering, and got their nicest control board. It helped a lot!

    The Extruder:

    Find the BOM in the Components Section, and the exploded annotated assembly model in the Files section. This design works but could be drastically improved. The goal was to do large-format 3D printing directly from recycled flakes, skipping the filament step. We've proven thats possible with this simple extruder, but lots of upgrades could be made to reduce weight, increase stiffness, and ease-of-mounting. 

    The extruder is designed to receive plastic flakes through a hopper connected to a cyclonic filter and vacuum system, that sucks plastic flakes up from a bucket, and drops them into the feed hose. It can also note enough material for small shapes, without refilling.

  • 3
    Building the Shredder

    The shredder I'm using is a "Precious Plastic" open-source shredder. The shredder box cost me about $400 to get the parts cut, and a few days to assemble. The electric motor and gear reducer was the hardest part to source, and cost me another $300. You don't have to use a PP shredder, but they're the best open source option I know of. An industrial shredder might work a bit better if you can find one, but the scale of the PP design is ideal for backyard processing. Wood chippers don't really work well enough for our purposes, as they are designed for wood and tend to try to "whack" things apart, which doesn't work well for plastics. Industrial paper shredders are and option, but their motors are often under powered and must be modified. Don't even try using a cheap paper shredder.

    Find full plans at, or in the files section. I highly recommend reading the Precious Plastic forums before building- you'll find a lot of improvements and hacks there.

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Jan wrote 02/05/2019 at 20:39 point

Hey there. Is the project halted? I'd love to see some updates and upgrades :)

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Sam Smith wrote 02/05/2019 at 22:13 point

Hey Jan, thanks for the reminder. I took a breather after making a sprint to make the Hackaday Prize deadline, but the project is still very much alive. There is additional info at, if you haven't checked that out yet, although I would like to add more to that as well. The project is in my backyard, not a shop, and so the cold weather has hindered my ability to tinker on the mechanical bits, so I've been focusing on instead on teaching myself how to set up IoT sensors so that I can start getting real numbers on the energy conversion (energy in v energy out). Based on my experience and research, and I am convinced that the process is very energy-positive, but I also understand that most people are rightly skeptical of experimental energy systems until there is hard data behind it, so I'm trying to get that data. I bought some ESP8266 boards and sensors, and so now I'm trying to get some friends who speak robot to help me program them. If you have specific questions about the project, feel free to ask them here and I'll do my best to answer.

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Tony wrote 06/25/2018 at 16:07 point

I'm afraid Manta103g has a few good points, but I don't think they're show stoppers. For instance, it'd be great to have this machine fuel itself off the plastics, but, if that's gonna spew toxic gasses then maybe we can find a way to just compress waste plastic into bricks. In fact I think they're already starting to make houses that way, so, theoretically we could start pressing plastic into slabs that a table top CNC machine could cut pieces that snap together to make tiny houses, or even little bike trailers people can sleep in and lock their stuff in for security... 

Then we'd have something we could get known for, enabling us to garner the attention and social capital to build something even more sophisticated, such as a robotic decomposer.  What do you think?

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Sam Smith wrote 06/25/2018 at 17:00 point

Manta103g does have a few good points, but they're not show stoppers, and it annoys me when people tell me so authoritatively that something isn't possible. 

To be fair, I'm learning too and by no means and expert, but I disagree with Manta103g's hot take, and with the caveat that I very well could be and am willing to be wrong, here is why: 

It's true that some plastics off-gas toxic vapors even when melted (not even burned). This is NOT true for all plastics, but it is for ABS, and it's true that ABS fumes from 3D printers are dangerous. It turns out that's actually caused by nano-particles or UFPs.

From wikipedia "ABS is stable to decomposition under normal use and polymer processing conditions with exposure to carcinogens well below workplace exposure limits.[20] However, at higher temperatures (400 °C) ABS can decompose into its constituents: butadiene (carcinogenic to humans), acrylonitrile (possibly carcinogenic to humans), and styrene.[20]

Lower temperatures have also shown that ultrafine particles (UFPs) may be produced at much lower temperatures during the 3D printing process.[21]Concerns have been raised regarding airborne UFP concentrations generated while printing with ABS, as UFPs have been linked with adverse health effects.[22]"

And all plastics, not just ABS, will decompose into a toxic smoke when heated.

But that doesn't mean that ABS cannot be safely decomposed into into a fuel, and in my mind, it actually is a decent argument for why ABS should be decomposed into fuel instead of being recycled, since melting/recycling it releases dangerous compounds whereas when used for fuel those compounds can be more easily contained. 

Check it out- ABS is Acrylonitrile Butadiene Styrene, chemical formula: (C8H8)x·(C4H6)y·(C3H3N)z). It's chemical structure is composed entirely of Carbon, Hydrogen, and Nitrogen. If you throw it onto an open pit fire, it will decompose into short-er but still fairly complex hydrocarbons, which can be all sorts of toxic compounds- styrene, benzen, toulene...

So don't do that! People have this idea that burning plastics is toxic, because it is when you do it in an open fire, at low temperatures.

If instead you shred ABS and heat it inside an air-tight reactor vessel, such that it gets hot and decomposes in the absence of oxygen, it will still break apart into smaller hydrocarbons, and some of them are toxic, but none of them are gaseous at atmospheric temperature and pressure.

If you cool the gas stream boiling out of the reactor in a condenser that cools the gas ALLLL the way back down to around 70F, which is what my condenser coil does, the only 2 compounds that remain gaseous at that temperature are Hydrogen (H2) and Carbon Monoxide (CO). 

H2 and CO are both combustible, and when mixed with O2, they combust into CO2 and H20- both non-toxic and 100% bio-compatible compounds. Now, I'm in favor of burning wood chips until I can guarantee the system is 100% safe and air-tight before working with more dangerous feedstocks, and I'm not there yet.

But ABS can in fact be thermally decomposed ALL the way back down to CO2, H20, and N2, and that makes those elements available to build built back into living things again. It essentially frees those organic elements so they can participate in the cycle of life again. 

And doing so releases heat, and also accumulates liquid hydrocarbons that condense out of the gas. I'm working on a centrifuge design that will sort them by their molecular weights, and then pump them into separate storage containers, so even the potentially dangerous ones can be stored without ever coming into contact with humans. 

The undesirable compounds- the ones that are either too heavy or too light to be useful by themselves, can simply be reflowed back into the reaction vessel, where they will break apart further into even smaller compounds, over and over, until they make it to CO and H2. And the desirable compounds- including analogues for gasoline and diesel fuels- can be filtered, stored, and used later as bio-fuel.

And the process necessarily produces waste heat and energy, which I intend to use to recycle as many of the other common recyclable and non-toxic plastics (HDPE, LDPE, PP, PET) into new objects- using molds, 3D printers, and extruders- which we could turn into building materials, and I think turning them into snap-together tiny homes is an awesome place to start!

Hope all that helps! Again, I'm not saying that doing any of this is trivial or easy, but I am saying that it is definitely possible, and I intend to figure out how to do it as best I can. 

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manta103g wrote 06/18/2018 at 23:35 point

No way to accomplish your target since some plastics, decompose to highly toxic gases, if heated. This is the reason, you should never print anything 3D in closed space to avoid inhaling highly toxic vapour gases. Many ppl are not aware, 3D printer should be operated in large,  ventilated space only.  Interest in ABS is below zero, since you cannot process ABS into fuel and workshops prefer clean ABS granules on input. Seperation of plastics is highly complicated issue, what comes next is cleaning and washing, just another highly expensive process. This is the reason China factories showed interest in PET bottles only, since PET can be processed alike nylon into usable PET yarn. I can tell you more and more and more about why the world doesn't love plastics processing. We have too much raw oil and gas to manufacture clean raw plastics, so interest in used plastics is low. What is hot today are metals and metals processing.

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Michael Barton-Sweeney wrote 05/02/2018 at 16:56 point

Nice project!

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