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.

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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 healthy living ecosystems, which regenerate wastes back into living things in an infinite loop powered by sunshine, humans societies mostly just make stuff out of stuff that we've dug up or cut down, and then throw that stuff away. All that stuff is piling up faster than it can be broken down again. Waste plastics are particularly problematic because very few organisms exist (with fascinating but negligible exceptions) that can break them down.

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. For 60 million years trees grew, died, fell over, but never decayed because no fungi or bacteria existed that could break down wood. (slightly oversimplified side note: Thats why we have coal.) It wasn't until white-rot fungi evolved special enzymes that wood became the compostable component of living systems that we know it as today.

Plastics are made of the same stuff as wood (oil is made from ancient living things after all), and it is extraordinarily energy-dense. 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 is eventually going to evolve that can metabolize the vast amount of plastics in our oceans and landfills, and convert the nutrients and solar energy they contain into structures that allow them to continue to live, grow, and self-replicate. It's only natural. But there's no reason that humans can't build systems that do just that, and that is the most intriguing idea I can think of. We built the systems that made the plastic, we can build systems that break them down. 

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. So....

Design Challenge:

Design a machine that mimics the metabolism of a living organism, that:

-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 to build. What I am currently building is a proof of the concept, to see if I can do it with what I know and what I have, and see if I can get other folks to work on this challenge that I think is so fascinating. 

What I am currently actually building a system that uses heat to break down shredded wastes into a combustible gaseous fuel (a mixture of Carbon Monoxide and Hydrogen), and then use that fuel to power an small lawnmower-type engine, then use the shaft power created by the engine to power a plastic/waste shredder and turn a generator to produce electricity, then use that shredded waste to make more fuel, use the electricity to power and control the system, and supply the shredded plastic flakes to a flake-extruding 3D printer head that is attached to a large-format Mostly 3D-printed CNC gantry, so that it...

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  • 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

  • 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 5 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

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

Nice project!

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