Metabolizer - A recycling center powered by trash!

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

Similar projects worth following
The Metabolizer is a proof-of-concept waste-to-energy power plant and recycling center that is powered entirely by trash. It is intended to have the same basic metabolism as a living organism, capable of breaking down wastes, including plastics, and turning them into useful things like heat, electricity, fuel, building materials, and 3D printed objects.

This project combines many existing components into a whole system that is more useful than the sum of it's parts. I call it the Metabolizer, because ultimately what we are doing is developing a closed-loop machine metabolism that breaks down complex molecules into simpler ones, inhales oxygen, and exhales CO2- like cyborg mushroom!

This project isn't ready for step-by-step instructions, so instead I layout each component of the system in detail, discuss what it is, what it does, and what it could ideally do, and what design challenges remain to be solved, so that we can all work on solving them together!

Problem Statement:

Unlike all healthy living ecosystems, which regenerate wastes back into living things in an infinite loop powered by sunshine (with fascinating but negligible exceptions), human-designed systems tend to just make new stuff out of stuff that we've either dug up or cut down, and then we just throw that stuff away when we're done with it. The problem is that we're running out of "away", and all that stuff we're making is piling up faster than it can be broken down again. Waste plastics are a particularly problematic example of this paradigm of consumptions, because very few living organisms exist that can break them down again, and none of them 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 produced 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. (slightly oversimplified side note: That's why we have coal.) It wasn't until white-rot fungi evolved special 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 as wood (and all living things), and are extraordinarily energy-dense. A gallon of plastic has roughly the same energy content as a gallon of diesel fuel. So whether humans survive the Anthropocene or not, we'd be flattering ourselves to believe that we could stop ALL life on Earth, and that means that SOME living organism will almost certainly eventually 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 how we got here. It's what life does. But we don't have to wait for humans to go extinct for this to happen! We built the systems that made the plastic, we can build systems that break them down. We can build systems that meet human needs, break down wastes, and fulfill and create ecological niches rather than destroy them. 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 fuel that can power internal combustion engines.

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

It's possible to use electricity and and shredded plastic to 3D print objects into very nearly any shape. 


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:

-is capable of metabolizing all common household wastes (cardboard, paper, plastic, glass, aluminum, etc, etc, etc) into the resources and energy required to power itself as long as there is "food" available.

-that is capable of synthesizing and replicating ALL of it's own parts, enabling it to grow, adapt, evolve, and self-replicate. 

-That is open-source, optimized for easy replication, and that is capable of monitoring and documenting it's own performance using a series of sensors that stream that data to the internet, so that successful systems can be replicated, and the success of improvements and adaptations can be easily quantified and compared by makers around the world.

The Prototype

Of course, what I am actually building is not that....yet. That is what I am TRYING...

Read more »

Adobe Portable Document Format - 142.84 kB - 04/20/2018 at 18:55


Adobe Portable Document Format - 117.67 kB - 04/20/2018 at 18:55


Adobe Portable Document Format - 614.00 kB - 04/20/2018 at 18:55


Adobe Portable Document Format - 22.42 kB - 04/20/2018 at 18:54


  • 1 × "Precious Plastic" shredder box Full plans available at
  • 1 × 5HP Briggs and Stratton engine Easy to come by on craigslist for free- $50 - search for used for lawnmowers, edgers, chippers, and rototillers, or search "Briggs and Stratton"
  • 2 × Band Heater Elements
  • 1 × 3" ABS Y-fitting
  • 1 × Black Steel Pipe Flange

View all 15 components

  • Well, that escalated quickly.

    Sam Smith2 days ago 0 comments

    I spent some time diving into the detail work on my model (which is now available on the SketchUp 3D warehouse), and I really like what I've ended up with. It's admittedly more ambitious, but I always wanted to make this project a work of art, not just engineering.

    I want to build something that embodies the energy flux of solar energy through living systems- a shrine to the chemical process of metabolism that makes all life possible. What better shape for that than a torus? 

    It also doesn't hurt that I built a 30' toroidal steel pavilion for a Burning Man art project in 2016, which has been pickling in playa dust under my porch for the past two winters, and has developed a very nice rusted patina.

    "Entrainment" installed at Shift Festival, 2016

    In fact, most of the components of this new system are cobbled together from bits and part I already have from older projects (seems appropriate). I've already got a Harbor Freight trailer, a 30' toroidal structure made up of twelve 1" steel 6' radius rings that break down into 10' sections, a 4500W propane powered generator I scored on Craigslist for $40, and about 100' of 1" stainless steel gas tubing I got at the Rebuilding Center for $6. 

    So I think I can put together an impressive installation for not that much money.

    The basic idea is that the machine will use computer-controlled heating coils (Ni-Chrome or Induction) to heat up 5.5 gallon kegs that are filled with compressed, shredded, and dried biomass, such as woodchips, yard waste, food scraps, and eventually even sorted non-recycleable or degraded plastics (HDPE, LDPE, and PP). 

    The application of heat in the absence of oxygen causes the hydrocarbons in the material to break apart and vaporize into smaller hydrocarbon chains, and escape from the keg in the form of a thick hot smoke. That smoke is directed into a series of stainless steel condensers (the smaller torus in the center of the structure), and as the smoke is pushed through this condenser it cools back down to ambient temperature, causing the hydrocarbons that make up the smoke to condense into liquids as they cool. These liquids drain back via gravity to the bottom of the torus, where they can be tapped off and collected to be refined into biofuels, or simply safely recirculated into the reactor.

    After the gas has been cooled back to room temperature, the only 2 gasses that remain are Hydrogen (H2) and Carbon Monoxide (CO), both of which are invisible, odorless, colorless, and highly flammable. When introduced to oxygen, they readily combust into Carbon Dioxide and Water Vapor, releasing heat in the process. An interesting property of Syngas (which is what the mixture of CO and H2 is sometimes called) is that unlike propane (C3H8) or gasoline (C8H18) or other complex hydrocarbon fuels, Syngas is made up of such simple molecules that when it burns, it should not produce soot of any kind. You know that kind of wavy, perfectly clear, hot exhaust that jet engine makes? It should look like that.

    And that's kind of a neat idea, I think, since people are (rightly) conditioned to not burn plastic or trash, because doing so without proper containment, condensation, and filtration IS very dirty and very toxic, and produces a toxic smoke. So the central hearth of the Metabolizer is designed to be made out of CNC-cut folded sheet metal polygons that glass panels will fit into, making the structure into 360 degree a viewing window that allows people to see the combustion going inside (which will hopefully take the form of a fire tornado). If the machine is built and operated properly, there should be no soot build up of any kind on the glass- which is sort of a showy way to prove to everyone that the machine is not releasing any toxic compounds into the air (Look ma, no VOCs!).

    Speaking of Jet Engines, I am suspicious that the two cones that make up the inside of the torus could be made into a sort of low-pressure jet engine,...

    Read more »

  • Party Time! Keg-cellent!

    Sam Smith06/05/2018 at 18:12 0 comments

    This project requires reaction vessels that can handle high temperatures, and are corrosion resistant. My original idea was to use 5-gallon stainless steel "Cornelius" style kegs as the reaction vessels to produce syngas, because kegs are readily available, and stainless steel can handle the temps I'll be working with. But I soon found out that the rubberized handles on Corny kegs are very difficult to remove- you basically have to burn them off, which is, uh, kind of the opposite of what I want to do (I would like the toxic smoke to stay INSIDE the machine, thank you very much). So I put out a call to facebook for REAL kegs, and my friends came through! I now have these 3 slimline style Sanke kegs to experiment with!

    When I got home, I started trying to figure out how to make a secure and gastight, but also quickly removable connection to the top of these kegs to collect the gas, and once I realized the taps I thought I could use weren't going to be secure enough, was afraid I would have to custom machine something, which is not only tedious and expensive, but also makes the project that much more difficult for other people to replicate.

    (this screenshot is from

    So I jumped on google, and was very pleased to discover that there is a HUGE range of every possible stainless steel fitting and connector I could possible hope for, readily available for not that much money, because of the home-brew industry. You can get stainless steel fittings in every shape and thread, butterfly valves, sight glasses, check valves, manifolds, and basically any other connection you can imagine, all with inter-compatible 2" tri-clamp connectors. Unnnnnng I'm in maker heaven. It's like a lego set for building complex, modular, high-temperature and corrosion-resistant machinery. 

    I ended up ordering a clamp system and this 1" NPT pipe thread fitting. This should let me securely and quickly attach my Corrugated Stainless Steel condensers to the kegs, without worrying about gas leakage or fabricating my own janky connectors. Once these parts arrive, I can start experimenting with making fuel! I'm going to start with wood pellets, because of their high energy content, flowable shape, and low toxicity. Stay tuned!

  • Oh shit, now I have to actually build this.

    Sam Smith05/30/2018 at 19:21 2 comments

    Welp, I just received my $1000 from Hackaday for being a finalist in the Open Hardware Challenge, and now I have to figure out what I'm going to build with it! I can't help but turn this machine into an art piece, not just a bit of engineering. I want to build something that will get people's attention and demonstrate what this thing is capable of. 

    What better shape than a torus to represent the infinitely reciprocal nature of living systems? The picture below is the concept I'm currently working with- a 4x4 harbor freight trailer carrying an engine, generator, battery bank, charge controller, gear reducer, and shredder, and a biomass reactor that produces the gas that runs the engine. The shredder shreds pre-sorted trash, the trash is fed into the reactor which breaks it down into gaseous fuels, gas is run through the condenser that collects and sorts fuels by their molecular weight, until the gas is clean enough to power and internal combustion engine. The gas powers the engine, then engine turns a common shaft, and off of that shaft rotational power is converted into 12VDC electricity by car alternators, which charge the batteries, which gives the machine the ability to constantly monitor its power output and turn the engine on and off as needed.

    The inner torus is a condenser coil that distills out volatile tars and heavy hydrocarbons, and sorts them by their molecular weight, hopefully this will produce fuels that are useful on their own. I'm planning to do this with a series of mason jars (because they are cheap and can handle relatively high temps). They aren't pictured yet in the sketch above, but it would look something like this:

    The outer torus is mostly just for show and structure (and to keep folks from getting too close to the reactor), but I'm going to put addressable LEDs along the poles so I can get a nice swirling light effect. I already have this structure from an art project I did for Burning Man in 2016, and it's currently just rusting under my porch, so I'm excited to get to use it again.

    The goal is to build a machine that can run all night long on the gas produced from thermally composing shredded burnable trash, including non-PVC plastics, in the absence of oxygen.

    It will start on propane, which will produce hot exhaust and electricity to power water heating elements inside the reaction vessel. Once the reaction vessel is warmed up the system will transition over to syngas fuel. New fuel material will be fed via vacuum lines and a cyclone filter to the top of the reactor, where it will fall down into the reaction chamber and turn into ash and gas, and the ash will be removed from the reactor every morning with a shop vac.

    That's the plan for now! Stay tuned! 

  • You condense if you want to, you can leave those tars behind

    Sam Smith05/01/2018 at 23:57 0 comments

    You condense! You condense! OK that's enough of that. Let's talk about condensers. A big part of this project is the condenser system. When you heat biomass or some plastics (imagine a keg filled with woodchips for now) in a closed vessel without access to oxygen, the molecules that make up the wood will start to decompose into smaller molecules. Here is the chemical structure of Lignin- one of the primary components of wood.

    Notice how this molecule is just a crazy arrangement of Carbon, Oxygen, and Hydrogen? It's made up of the same molecules that oil and gas (and you) are, but it's much larger and heavier. In order to use it as a fuel, we need to break it down into smaller bits. In a perfect reactor, these wood molecules would get so hot so fast that they would all break ALL the way down to their simplest possible components- Hydrogen gas (H2) and Carbon Monoxide (CO), which is what we will use to run our engine.

    In practice, however, there will always be uneven heating, especially when the reactor is just heating up. So complex hydrocarbons will tend to break apart into slightly-less complex hydrocarbons, which looks like a thick, acrid smoke. These complex hydrocarbons are gaseous at high temps, but will condense out of the smoke at lower temperatures. So if you can heat up biomass, and then cool the smoke that comes off ALLLLL the way down to ambient temperatures (around 70F), all of the gummy, nasty, sticky, and sometimes toxic tars and solvents will condense out of the gas, and the only gasses that remain gasses at ambient temps are the CO and H2 that we will use to run the engine.

    So we need a cheap, safe way to condense out these tars. You can create a system that captures these molecules and sorts them by their molecular weight, which allows you to produce analogs for diesel and gasoline, but that's a phase 2 project. For now, we want to build a system that will:

    -Be able to handle high temps without corroding

    -Be readily available so that people can replicate it

    -Be easy to work with and require minimal tools or welding

    -Have a high surface area and/or thin walls for high heat transfer

    The best solution I have come up with to solve this problem is using "CSST" flexible gas tubing. This stuff is so great. It's marketed as a flexible piping system for natural gas, and you can buy it in 75-ft rolls at home depot or lowes. But the great thing about this stuff is that once it is removed from a house, it generally can't be re-installed to code, so if there is a ReStore or other material salvage spot in your city, it's pretty easy to find used. I scored a huge roll of it at the Rebuilding Center in Portland.

    Cut away the plastic sheathing (and keep it, I think it's Polyethylene, and we can shred it later...) and you've got an uncoated, high surface area hand-flexible stainless steel condenser! For simplicity's sake, I'm going to try and build a back-flow design, where the gas is cooled in an upward spiral, and the condensed tars drip back into the reactor. But in the future I'd like to design a multiple condenser system that collects the tars as they cool, to harvest valuable liquid fuels and chemicals. But doing so is complicated and dangerous (some of these compounds are VERY VERY toxic. Please don't f*ck around with them, or, if you do, please at least be professional about it)

  • Scooooore!

    Sam Smith04/25/2018 at 07:57 0 comments

    I just scored this working propane-powered electric-start 4500W generator unit on craigslist, including a new starter battery and a 1/2-full tank of propane for $60! Apparently there is an issue with the generator unit that makes the breaker trip- seems like an internal short. It might be fixable, but the guy didn't want to have to deal with it, so he sold it to me cheap. This is a huge score for me, because I was going to remove the generator part anyway, at least to extend the driveshaft so I could also connect the gearbox and shredder. 

    So if I can get generator part working, that's a bonus. But the reason I'm interested in this engine specifically is that it's already set up to run on gaseous fuels, which makes it much easier to run it on charcoal, syngas, or biogas without having to modify the carburetor or air intake.  It also has a 1- 1/2" NPT threaded pipe fitting already fitted onto the exhaust, which makes it easy to just screw on my own fittings and capture the waste heat from the exhaust stream. It also gives me the option of recirculating the exhaust gases into the biomass reactor, which allows for precision control of the air -fuel mixture within the reactor. 

    Here's a photo of the engine I've been working with so far- notice the janky pipes I've stuck on there- none of them are very secure. This is a major upgrade for $60! Stay tuned!

  • It lives!

    Sam Smith04/24/2018 at 04:19 0 comments

    It doesn't run on char-gas yet, but it does power the shredder no problem. And later (not pictured) I hooked up the generator and was getting around 40VDC at full throttle, 20ish at idle. Those are promising voltages because they can easily be handled by a charge controller designed for solar. 

  • First test of char-gas

    Sam Smith04/24/2018 at 04:17 0 comments

    This is just a short (kinda poorly thought out) test of using charcoal to produce a flammable gas. It works! But I need to redo my fittings.

  • Troubleshooting the MPCNC Gantry

    Sam Smith04/24/2018 at 04:16 0 comments

    Troublehsooting the gantry! It moves...kinda!

View all 8 project logs

  • 1
    The Engine

    What it does: The engine turns chemical energy into rotational shaft power (and heat). 

    What it is: I'm currently using a 5HP Briggs and Stratton go-kart engine. These engines are cheap and they're everywhere- usually attached to go-karts, lawnmowers, chippers, etc. You can find them on craigslist for $0-80, and new from places like Harbor Freight for $100-200 Get one that doesn't require oil mixed in, and if you can find one with easy-to-modify exhaust and air-intake ports, that's a big plus, because we're going to be modifying them so that we can run the engine on a gaseous fuel.

  • 2
    The Gearbox

    What it does: The gear box takes the 2000-3000RPM shaft power from the engine and uses a series of gears to reduce the speed and multiply the torque. A gear ratio in the range of 30:1-50:1 is ideal, with an output RPM in the ballpark of 100RPM. This gets us the torque we need for the shredder to shred right through anything.

    What it is: There are many strategies for gear reduction- car transmissions, gear and pulley systems, hydraulics, worm drives.... It's a whole thing. I'm using a worm-drive style 40:1 industrial gearbox I found at salvage yard for $5. That was a lucky score- finding a good gearbox is one of the more difficult/expensive parts to source. Check craigslist.

  • 3
    The Shredder

    What it does: The shredder shreds up waste into small bits so that it is easier to process, and reduces waste volume significantly. Think of it as the metabolizer's teeth. It mechanically decomposes incoming feedstock to prepare it for further chemical decomposition.

    What it is: 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. 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.

View all 5 instructions

Enjoy this project?



manta103g wrote 13 hours ago 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.

  Are you sure? yes | no

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

Nice project!

  Are you sure? yes | no

Does this project spark your interest?

Become a member to follow this project and never miss any updates