Urban Biosphere : The manual grinder

BIOSPHERE EXPERIENCE

https://wiki.lowtechlab.org/wiki/Biosph%C3%A8re_Urbaine_:_Le_broyeur_manuel/en

Dernière modification le 18/10/2025

Difficulty

Very hard Very Hard

Duration

2 day(s) day(s)

Cost

60 EUR (€)

Description

This machine has been specially designed to manually grind organic kitchen waste, producing a mash that is easily assimilated by black soldier fly larvae. In just a few hours, these larvae transform this material into a rich, natural organic fertiliser.

Summary

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Introduction

Project

The BIOSPHERE EXPERIENCE association experiments with sustainable and desirable futures in which humans live in symbiosis with other living species. In 2024, Caroline Pultz & Corentin De Chatelperron spent four months experimenting with what a low-tech lifestyle in an urban environment might look like: a lifestyle without waste, reducing water consumption tenfold, meeting the UN's 2050 targets for greenhouse gas emissions, while remaining desirable and accessible to all. With the help of experts, volunteers and interns, they imagined and designed a forward-looking ecosystem apartment called Urban Biosphere, located in Boulogne-Billancourt in the Paris region. To complete the ecosystem, their colleague Emma Bousquet-Pasturel set up a vast network of citizen support around the apartment. At the same time, Emma was tasked with coordinating a participatory science programme bringing together hundreds of citizens from France and elsewhere to test a simplified version of some of the low-tech systems from the laboratory-apartment in their own homes.

This tutorial presents a low-tech module specially designed for the four-month experiment conducted by Caroline and Corentin in a pilot flat in Boulogne-Billancourt.

The manual grinder :

The low-tech flat was designed to recycle every piece of waste produced. In this tutorial, we will focus on recycling organic waste. On average, a person generates around 700 g of organic waste per day (peelings, eggshells, etc.). Instead of throwing it in the bin, this waste can be reused. In the ecosystem flat, this waste was used directly to feed the black soldier fly larvae present in the living toilets. These larvae play an essential role in transforming bio-waste into highly nutritious fertiliser for plants. To facilitate their transformation and enable their rapid use, we prototyped and built a manual grinder with the help of Zoé and Paul from L'Avant d'Après. The manual grinder reduces organic waste to a fine paste, which is more easily assimilated by the larvae. Thanks to this process, they can transform waste into organic fertiliser in just one day.

Improvements to be made: This first version of the grinder still has a few areas for improvement. After several uses, we noticed that organic matter tends to dry out inside the grinder and at the outlet, which slows down the flow and can even block the system completely. In addition, for this version, the pedal assembly was mounted upside down, requiring the user to pedal backwards to operate the grinder. To avoid this error in the future, it is recommended that the right and left sides of the pedal assembly be clearly marked before cutting into the bicycle frame.

User feedback: When the system is working properly, it offers an ergonomic and enjoyable experience. The double cranks allow you to get some ‘useful exercise’ right in your kitchen, and even warm up when it's cold! The resulting mash is perfect: the larvae love it and devour it in no time. It's really impressive!

This tutorial describes how to make a manual grinder in three main steps. The model presented in the tutorial can be adapted, modified, and improved according to your preferences, materials, and skills. The price varies depending on the proportion of recycled materials used (in this case, the bicycle parts are recycled). The price of €60 corresponds to the purchase of the hand-crank meat grinder (approximately €35), wood, and pieces of steel.

In the image above :

1. The double crank pedal installed on the worktop
2. The grinder (meat mincer) installed under the worktop
3. The purée falls through a galvanised pipe into the larvae tray with a drawer (here, it is the same larvae tray as the one in our toilets)

Youtube

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Materials

Here is a comprehensive list of the materials you will need. If you already have some of these items, we recommend using second-hand materials and adjusting their diameters and dimensions as you follow the tutorial.

1. Dismantling the bicycle and recovering parts
   • Bicycle parts to recover (see diagram):
     • Sprockets
     • Chain links
   • In one piece:
     • Chainrings
     • Bottom bracket
     • 2 pedals
     • 2 cranks
     • piece of the bicycle frame to be used as a base
2. Part A:
   • Ergonomic crank
     • 2 pedals
     • Wooden cylinder with dimensions suitable for the pedal support (see photo; here, recycled chair legs were used)
     • 4 screws, size 3.00 x 20 mm
   • Wooden support
     • Wood for machining
     • Wooden dowels
     • Wooden dominoes
     • Glue
     • Abrasive sheets/sandpaper for sanding
   • 3- Assembly of crank block + pedals on wooden support
3. Part B:
   • Welding of outer sprocket part
     • Bicycle cassette (all sprockets)
     • Metal parts (2 metal washers and small steel part)
   • Welding the inner part of the sprocket
   • Assembling the sprockets on the grinder
     • Meat mincer no. 2 (here, obtained from a butcher)
     • Grinder screws
4. Final assembly:
   • Bicycle chain
   • T-TUBE
   • Container for collecting the shredded material

Tools

This is a comprehensive list of tools to adapt according to what you already have.

• Welding machine
• Screwdriver / Drill / Electric screwdriver
• Scissors
• Soldering iron (not essential)
• Hand saw or jigsaw
• Hole saw
• Tape measure or ruler
• Calliper
• Drill bits of various diameters
• Clamp or glue clamp (optional)

Step 1 - Material collection and purchase

1 - Bicycle parts

If possible, collect parts from an old bicycle, or purchase spare parts.

First of all, it is important to understand that the manual shredder consists of two parts. Part A is a set of components including a crank connected to a bicycle wheel resting on a wooden support. This part is then connected by a chain to part B, which consists of sprockets welded onto a grinder. You can see them in the first image, on which the worm gear inside the grinder, connected to the bicycle sprocket, and the hole mouth are missing in transparency.

Part A

If you are collecting parts from a bicycle: saw through the frame at the bottom bracket to obtain a single piece comprising the bottom bracket, chainrings, crank and part of the frame. Then collect the central part of the pedal, shown in red in the photo.

Otherwise, purchase a pedal crankset, pedals, and a cylinder to connect the two arms of the crankset.

Reminder: It is recommended that you clearly mark the right and left sides of the crankset before cutting into the bicycle frame to ensure the pedals are facing the correct direction.

Part B

Obtain or dismantle a bicycle cassette (set of sprockets).

2 - Ergonomic Pedal

Measure the diameter of the central part of the pedal with a calliper.

Starting from this diameter, choose a hollow wooden cylinder (see illustration). Here, we used recycled chair legs that were the right size.

Step 2 - Assembling the pedals (Part A)

1 - Drilling holes in the wooden cylinders

In each of the wooden cylinders, use a drill bit to drill two holes with a diameter suitable for your screw (here, a 3 mm diameter screw) and corresponding to the notches in the pedal support.

2 - Assemble the pedal shafts to the cylinders

Assemble the pedal support with the wooden cylinder by screwing in two 3.00 x 20 mm screws.

Repeat the process to make the second crank.

3 - Screw the pedals onto the cranks

Step 3 - Construction of the wooden support (Part A)

1 - Cutting the pieces

Shape the wood into different pieces (numbered in the image) to create a support:

• Piece 1 x2
• Piece 2 x1
• Piece 3 x1
• Piece 4 x1
• Pieces 5: Collect wooden pegs to fasten the pieces of wood together.

2 - Assembly of parts

Assemble the pieces using wooden pegs.

To assemble the different wooden parts, you can also use dominoes (piece 6), which you position in the oblong holes. This provides a better hold but is more difficult to do.

3 - Optionnal Step : glue the wooden parts together

This step is optional if you want the grinder to be demountable. Finish the assembly by gluing the last parts of the base with wood glue and leave to dry, pressing down with clamps or glue clamps.

Step 4 - Assembly Crank and wooden support (Part A)

1 - Drill the wooden support

Mark the spot where you will need to drill into the support to pass through the crank (marked in red).

Drill a hole in the wooden support using a “”'hole saw'“” so that the first crank can be inserted.

2 - Insert the bicycle frame with crank into the wooden support

Close the wooden support, which now encompasses the entire bicycle frame.

Step 5 - Machining the cassette (Part B)

1 - Carefully identify the parts to be machined

• Metal piece A with a diameter equal to the diameter of the smallest sprocket
• Bicycle cassette
• Metal rod
• Grinder screw

2 - Welding metal part A to the cassette

Weld metal part A to the cassette on the side of the largest sprocket, ensuring that the part is centred.

3 - Drilling the assembly

Start by locating the centre of metal part A using the teeth of the large sprocket: draw a line between one tooth and its symmetrical counterpart relative to the centre, then repeat the operation for greater accuracy.

Once the centre has been marked, gradually drill with different drill bit diameters, increasing in size to make a clean hole, until the metal rod B fits.

4 - Welding the second metal piece to the cassette

Repeat steps 3 and 4 on the small gear side.

5 - Welding the metal rod to the assembly

Insert the metal rod into the centre of the sprocket, between the two metal parts A and C.

Weld a piece of metal (D) onto part A in order to secure this metal rod in the pinion shaft.

Step 6 - Assembling the cassette to the grinder

Now assemble the sprocket onto the grinder using the grinder screw. Screw the sprocket onto the grinder.

Pay attention to the direction of assembly: the sprocket with the smallest diameter must be in contact with the grinder.

Step 7 - Installation of the assembly

In the low-tech flat, we installed the cranks at arm height on the worktop for ergonomics, then adjusted the chain to connect it to the grinder under the worktop. The purée falls through a galvanised pipe into the larvae tray with a drawer (here, it is the same larvae tray as the one in our toilets). The drawer (opening towards us) allows us to monitor the transformation of organic waste, with a view of the larvae.

1 - Carefully check the assembly

On the first image :

1. The double crank pedal installed on the worktop
2. The grinder (meat mincer) installed under the worktop
3. The purée falls through a galvanised pipe into the larva tray with a drawer (here, it is the same larva tray as the one in our toilets)

2 - Install the assembly

Provide a hole in the worktop for inserting organic waste, and another for passing through the bicycle chain.

Install the entire assembly, including part A connected to part B using a bicycle chain, by embedding part A into the worktop using a T-shaped steel tube (see photo in the list of materials).

Provide a container to collect the shredded material.

Notes and references

The prototype was developed in collaboration with L’Avant d’Après and Jérôme Lhommeau (Contes et nerfs d’acier) as part of the Urban Biosphere experiment.

Tutorial written by Bertille Maria, with help from Paul Mouraz (l’Avant d’Après), Enzo Audion and Caroline Pultz, published by Agathe Meurisse. Translated into English by Eva Joskin.

To learn more about breeding black soldier flies: https://wiki.lowtechlab.org/wiki/Elevage_de_Mouches_Soldats_Noires

To learn more about living toilets : Sciences Participatives : Toilettes vivantes

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