Low tech plastic recycling

Posted on August 15th, 2022 by Nathan Lioret

In this third and last article on the manufacturing and recycling of plastic, we will see different low-tech methods of plastic valorization. We will see the methods we came across during our researches for the Tri-Haut pour l’Everest project, without claiming to give an exhaustive list of all the existing methods neither.

Let’s first look at the preliminary steps of most recycling methods : sorting, shredding and washing. Regarding sorting, we studied it extensively in the previous article, [Sorting plastic], I invite you to read it if you haven’t do it yet.


When shaping plastic objects, the raw material is generally made of small homogeneous plastic flakes that are melted and shaped using different processes (see our previous article [Plastic in all its forms]. Many recycling processes, low-tech or not, use the same shaping principles, but to do this, the waste must be transformed again into small homogeneous plastic elements : the small size of the elements is ensured by the shredding step, performed by a shredder. Check out this rather satisfying video of a shredder swallowing a plastic bottle and spitting it up into small flakes :


There are many shredder technologies, at very different scales because this step is essential for any recycling center, whether it is a small low-tech center like the one we will build with the Tri-Haut, or a large industrial center.

Among all these technologies, we chose the one proposed by the Precious Plastic community, a global community for low-tech plastic processing that greatly inspired us as we will see in a next part. Its principle is quite simple, it involves rotating two sets of curved blades in opposite directions to vacuum while cutting the waste into small pieces.

Tri-Haut shredder
1. Frame Table 2. Shredder box 3. Hopper
4. Transmission 5. Transmission protection
6. Gearbox 7. Motor 8. Electric panel

There are centers only specialized in crushing the plastic wastes, which then sell the small pieces obtained to manufacturers so that they can make new objects from them. It is common for PET plastics (plastic bottles), which are the most recycled, because their purchase is often more expensive new than recycled, which is not necessarily the case for other types of plastics.


As we saw in the previous section, most recycling processes require raw materials (made from plastic waste) made of small pieces of homogeneous plastics. Washing, combined with sorting, ensures the homogeneity of the plastic. It consists in removing the added elements from the objects (labels, aluminum film, etc.) and cleaning it of impurities (soil, dust, food remains, etc.).

Once again, different technologies exist at all scales because it is a step almost as essential as shredding. It is usually done after the shredding so that all surfaces can be cleaned up (for example, the inside of a closed bottle is inaccessible before shredding).

The first step is to clean the plastic flakes, usually with water, either in the style of a washing machine with a rotating drum, or by stirring a tub of water in which the flakes float. It is this second option that Plastic Odyssey, an organization fighting against plastic pollution, which we will describe more precisely later, have chosen with their washing machine. This method works well with lightweight plastics (PP, PE, PS) which float on the surface while impurities sink. It works less well with PET and PVC which are also heavier than water.

A second centrifugation step separates the last impurities as well as the humidity due to the first step. For this, a centrifuge is used, both on a low-tech scale and on an industrial scale. The vertical centrifuge presented by Plastic Odyssey simply consists in rapidly rotating a cylinder surrounded by a hopper large enough to allow impurities and water to pass through but still smaller than the plastic flakes. Thus, pure, dry and dirt-free plastic is obtained, the ideal raw material for the following machines.

Precious Plastic

We already talked about Precious Plastic machines in the shredding part without explaining what this community really was.

Precious Plastic is a low-tech plastic recycling project, meaning on an artisanal scale. It was launched in 2012 by Dave Hakkens and aims to democratize plastic recycling by allowing anyoneto set up his own miniature recycling plant. To do this, plans for inexpensive machines as well as tutorials on how to assemble them and how to operate them, or how to manage different types of recycling workshops, are available in open source on their website (https://preciousplastic .com/index.html). You can also buy the machines directly from people who make them, which is what we did for our project. Finally, the idea of Precious Plastic is to bring people together in local communities for the recycling of plastic.

Precious Plastic presentation

Among the machines presented by Precious Plastic, we obviously find the shredder and the washing machine that we previously saw, but also four machines intended for shaping plastic :

  • The extruder transforms the shredded plastic into a wire in the shape of the mold placed at the outlet. The principle is quite simple : an endless screw heats and conveys the shredded plastic to the mold which, under the pressure exerted by the continuous supply of material, comes to give its shape to the plastic, which cools once in the open air , to freeze its shape. Starting from this wire, or from profiles of different shapes, it can be kept as it is or rolled up on itself like wicker. You can also place another mold, a closed one, at the exit of the extruder to create beams, which can then be twisted and assembled (see the following video).
Creation of beams with the extruder
  • The plastic sheetpress makes it possible to manufacture sheets from palstics, as its name suggests. It is simply a matter of compressing plastic between two plates, heating it so that it can stick together. These plates can then be cut, twisted by heating them locally using moulds, and assembled to create objects, in particular furniture or containers.
  • Precious Plastic’s injection molding machine is a miniature version of those used in industry, just like the extruder. It makes it possible to create small objects by injecting heated plastic into a mould, again using an endless screw. The plastic will then take the shape of the mold and give the desired object once cooled.
  • The compression machine looks a bit like the sheetpress. It involves filling a mold made up of two parts (bottom and top) with plastic flakes and putting the whole thing into an oven between two plates which will compress the whole thing so that the plastic takes the shape of the mold once cooled.

The main problem with Precious Plastic machines is their inability to process PET plastic, which is very difficult due to a very precise melting temperature range compared to other plastics, and a tendency to crumble when cooled down. Only the injection molding machine can possibly be used with PET, for very small objects. Precious Plastic machines work best with PP and PE.

By combining the use of these machines, one can create an infinity of plastic objects : table, spinning top, key ring, chair, basket, crates, bricks, “works”…

Plastic Odyssey

Plastic Odyssey is an organization from Marseille which fights against plastic pollution at sea. To do this, it seeks to act upstream, that is to say directly with the populations who produce the plastic wastes, by encouraging them and helping them build their own low-tech recycling machines. They also work with populations to find solutions to reduce their plastic consumption, particularly regarding the single-use plastics.

You can find on their website (https://plasticodyssey.org/), in the same way as for Precious Plastic, a whole set of low-tech machines in open source. Among them, we find again a shredder and a washing machine, but also an extruder, an hydraulic press, a plate oven, a compactor and a pyrolysis.

  • Plastic Odyssey’s extruder works roughly in the same way as Precious Plastic’s one although it is much more powerful (about 5 kW for Precious Plastic’s pro extruder vs just under 50 kW for Plastic Odyssey’s) , but therefore also more expensive, heavier, more voluminous… A barrel is also offered by Plastic Odyssey, it is a support for the molds making it possible to produce profiles of various sizes and sections, it makes it possible to optimize the use of these molds by avoiding having to stop the extruder each time the mold is changed (but simply to turn the barrel), unlike the Precious Plastic extruder.
  • Plastic Odyssey’s plate oven creates plates from plastic flakes. It is simply a matter of heating the plastic in a mold in the form of a plate. But unlike the Precious Plastic sheetpress, here the plates are not compressed. If you want to obtain smooth and compact plates, you have to place them still hot in the hydraulic press that we will see just after. With Plastic Odyssey’s technology, it therefore takes two machines to do what Precious Plastic does with a single machine. But the hydraulic press can be used differently too, as we will see shortly.
  • The hydraulic press already makes it possible to greatly improve the quality of the plates produced by the plate oven, as we saw ust before. But its scope is much wider than simply creating flat plates. The major interest of the hydraulic press appears when you place a mold (in two parts : fixed and mobile) between the two plates and you put material between these two parts of the mold. Either material coming out of the extruder or a plate coming out of the plate oven, in all cases it must still be hot and malleable. By then exerting a strong uniform pressure on the mould, thanks to hydraulic cylinders, the material is forced to be distributed throughout the mold cavity. One thus obtains, once cooled, very diverse objects according to the molds chosen. It is similar to the compression machine from Precious Plastic, but without heating.
  • The compactor does not really recycle the plastic, it simply makes it possible to compact the waste into compact bales so that they take far less space if we want to transport them or simply store them. This considerably reduces the volume occupied by the waste, but it then becomes more difficult to separate them in order to sort them because they are tangled in the bale.
  • We will talk more about the pyrolysis in a future section, and even more in our dedicated article [The pryolysis].

Polyfloss Factory

Polyfloss Factory is a small British company, initially created by London students, which created a machine for transforming PP and PET plastics into insulating wool for buildings and clothing (down jackets, sleeping back, etc.).

Brut report about Polyfloss Factory

This machine is of great interest for low-tech plastic recycling. It is the only machine to easily and efficiently recycle PET plastics, which are very difficult to process with Precious Plastic and Plastic Odyssey machines due to their very precise melting temperature and tendency to crumble on cooling. However, it is optimized for the treatment of PP. In addition, it makes it possible to process fairly large quantities of plastic (10 kg/hour) and this continuously, we only need to feed it with plastic. It consumes relatively little electricity (600 W, compared to 5 kW for a Precious Plastic extruder for example). Finally, it is easy to use and maintain.

Regarding its many advantages, it is obvious that such a machine will be present in our sorting center at the bottom of Mount Everest !


It is not really a low-tech recycling method, but it’s interesting to see what some people manage to create as works of art from simple plastic waste collected in landfills like we find so much in Nepal, and in many other countries of the world sadly.

The best example for this is the Sagarmatha Next project, which is located in the same valley as our project, a little below. Take a look on there website if you’re interested : https://www.sagarmathanext.com/.

The pyrolysis

With the pyrolysis, we are entering methods that are a little further from actual recycling, but which still allow a certain valorization of the wastes. It makes it possible to treat the waste that are difficult to recycle (too dirty, too mixed, already recycled several times, etc.).

We saw in the first article of this series of three articles on plastic, [Plastic in all its forms], that plastics are in fact an assembly of hydrocarbon molecules placed end to end to form a long chain, namely polymers. The idea of the pyrolysis is to perform the reverse process : by heating the plastic in the absence of oxygen, to over 450°C, the plastic evaporates and its bonds break : part condenses into fuel oil, another part remains in gaseous form, and a last small part forms wax, a solid substance which we do not yet know what to do with.

It is common to carry out the pyrolysis process (heating and condensation) several times in a row using several condensers (3 for our prototype) in order to improve the quality of the fuel oil. The gas produced can also be used to heat the combustion chambers. In our case, as electricity should not be a problem due to the upcoming construction of an hydroelectric power station in the valley, we are trying to recover this gas to allow the inhabitants to heat themselves in particular. Our research continues on this point, and on the wax as well.

The advantage of the pyrolysis is that it requires less pre-treatment phase than for recycling machines : if the shredding upstream is highly recommended, washing is not essential, although it allows to improve the results obtained, as shown by our experiments on the prototype. This is a very efficient process for PP and PE plastics but does not work very well with other plastics like PET…

The pyrolysis prototype developed by the first Tri-Haut team.

As this technology is not yet fully mature, due to difficult industrialization and low oil prices, we are doing a lot of research and experiments on pyrolysis.

If you want to know more, last year we wrote an article dedicated to this process on our website, [The pryolysis]. We will update it as we progress.

The incinerator

Incineration is not a recycling method as such, either, but it can make it possible to recover energy from plastic wastes by recovering the heat produced, either directly by injecting the heat into a heat network, or by transforming it into electricity.

We won’t dwell on this widespread technology because we already did it in a previous article, [The Incinerator], when we were still planning to install an incinerator in the valley.

Plastic sorting

Posted on August 8th, 2022 by Nathan Lioret

In the previous article, we presented to you quite briefly how plastic materials are made, which constitute the bulk of the waste that we will process in Nepal. If the terms polymer, thermoplastics, thermosets, injection, extrusion, rotational molding… are not familiar to you, I invite you to read our previous article [Plastic in all its forms].

Before starting to recycle plastics, which will be the subject of the next article, we must sort them according to their type because each type of plastic has specific properties which generally do not allow several types of plastic to be mixed in the same recycling process. We can already think of the importance of distinguishing thermoplastics and thermosets : one can be remelted indefinitely and is thus very suitable for recycling, while the other is fixed forever after its creation, which makes it very difficult to recycle. We will also see that it is very important to clearly distinguish the 7 categories of thermoplastics, some more than others, especially due to different melting temperatures from one category to another. We are getting to the heart of the matter.

Thermoplastic or thermoset ?

A first sorting must be carried out between these two extremely different types of plastics that can never be mixed within the same recycling process. Fortunately, it’s easy to tell them apart, using one of the following two methods.

The first, the most logical, is to heat the plastic to see how it reacts : thermoplastics melt (transition from solid to liquid) while thermosets burn, they blacken without changing of state.

The second method is to scratch the surface of the plastic. When the surface of a thermoset is scratched, particles appear, they stay on the finger when we pass it over the scratch. It is not the case for thermoplastics. [1]


Now that we have separated thermoplastics from thermosets, we will sort thermoplastics according to their type. We will not be interested in the sorting of thermosets because it is very little developed. Indeed, it is impossible to recycle them and they generally end up incinerated or put in landfills, so there is no need to sort them…

Sorting thermoplastics is a very complex task that can be approached from different angles, we will see the main existing methods, their advantages and disadvantages and finally which ones will be used for our project.

Manual sorting

The method which requires the least technology is manual sorting, “by hand”, carried out by a human who will recognize, according to its color, its texture, its shape, its added elements (labels, recycling symbol, etc.), what kind of plastic it is. This work can be greatly facilitated, especially in Europe, by the appearance of acronyms designating what type of plastic it is. This method is essentially based on the experience of the person doing the sorting, it can be very quick if several people get involved, but it sometimes happens that two different plastic products have the same appearance and the same texture. Errors are therefore quite frequent with this type of sorting.

To see from what plastics the most common objects are generally made of, I invite you to go back to our previous article [Plastic in all its forms] where the classic uses of each type of plastic are detailed in the section “All the same plastics ?”.

The manual sorting method, which is inexpensive and energy efficient, is the method that we will use the most in the context of the Tri-Haut pour l’Everest project.

Source : https://www.lagazettedescommunes.com/300180/le-centre-du-muy-trie-les-plastiques-souples-a-cout-maitrise/

Sorting by flotation

A second widely used method is the sorting by flotation. It turns out that the density of plastics differs from one type of plastic to another. The idea of the sorting by flotation method is to exploit this property to, using successive receptables filled with different liquids, separate the different types of plastic. Indeed, the heaviest plastics will sink while the lightest will float, they can then be easily separated.

For this method to be effective, the difference in density between the materials to be separated must be at least 0.2 g/cm3, particularly to be able to neglect the effect of additives on the density. We can therefore see that it will be difficult to precisely separate PE from PP and PS, for example. However, this method is widely used to separate PET from other plastics (except PVC), simply with water. Other separations, more or less precise, can be carried out using other liquids but we will not dwell on them further.

Densimetric sorting

There are other densimetric sorting methods, which are based on the mechanical behavior of a solid in a fluid (liquid, gaseous or supercritical) according to its shape, its density and its surface of contact with the fluid. The shredded plastic is sent in a flow (horizontal, ascending, centrifugal…) in order to be sorted. Some examples of processes using this method are given below :

Air Knife (top left), Zig Zag (right), Cyclone (bottom left) and Fluid Bed Density Table (bottom) methods [2]

Burning method

Another fairly simple method to implement is the method of sorting by burning. It simply consists in burning a piece of plastic to be sorted in order to determine its composition according to the properties of the flame (color, volume, appearance). This method presents risks since certain types of plastic release toxic fumes when burned (PET, PVC and PS in particular). In addition to this risk, this method is very difficult to industrialize and less effective than other methods that are easier to implement on an industrial scale, so it is not used in the industry. However, it can be used occasionally in sorting situations with low-tech machines, especially to clear up doubts when sorting plastics manually. It is in this second situation that we find ourselves with the Tri-Haut project.

Flame properties depending on the type of the plastic burned [3]

Optical sorting

Let us now see the methods of optical sorting, they can be distinguished into two categories : optical sorting upstream and optical sorting downstream.

The first type of optical sorting method consists in observing the shape, size and color of incoming waste, not yet shredded, to try to determine its type, just as a human would do. These technologies have developed in recent years with the rise of artificial intelligence.

The second is carried out downstream, generally by Infrared spectroscopy (detection of the vibrations of certain chemical bonds at characteristic frequencies) even if other methods exist. In particular infrared pyrolysis which consists in analyzing by infrared spectroscopy not the solid matter directly but the gases emitted during the pyrolysis (combustion without oxygen) of this plastic material using a laser. But also Raman spectroscopy and in the visible (same principle as in Infrared but for different chemical bonds), X-ray fluorescence (detection of atoms that can fluoresce), ultrasonic analysis (measurement of the attenuation of ultrasonic over a given frequency range)… Each type of plastic has different responses to each of these solicitations. However, it is not always so easy to differentiate them, once again because of the different additives that are very often found in plastics and which affect the properties of the material and therefore its response to optical (but also mechanical) solicitations. , electric, etc.). [2]

Electrostatic sorting

Finally, after the methods of manual sorting, densimetric sorting (flotation, air or water flow, etc.) and optical sorting (burning, upstream, downstream), sorting methods using the specific electrical properties of each type of plastic exist. To exploit these properties, it is necessary to charge the plastic particles, several ways of doing this exist : by triboelectricity (intensive friction of different particles between them, in the manner of a balloon with our hairs), by conductive induction (setting a charged surface with the uncharged particles of the plastic) or by ion bombardment (the reverse of conductive induction : the plastic is charged but the fixed surface is not). Then, if the size of the plastic elements is small enough for the electrostatic forces to be greater than the forces of gravity and inertia, if they are dry and of homogeneous granulometry, then the plastics can be sorted by this method. [2]

Electrostatic charge of the main plastics (charged (-) to the left, charged (+) to the right) [2]
Hamos Electrostatic Separator [2]

Sorting by selective dissolution

The last method presented here is the so-called selective dissolution sorting method. It consists in placing the mixture of plastic that one seeks to sort in different solvents at specific temperatures, in which certain types of plastic will dissolve and not others, to highlight the types of plastic present in the mixture. . By successively applying this method until the mixture is completely dissolved, it determined which plastics are present.

Some classical solvent/non-solvent pairs [2]

We can also mention magnetic sorting, which does not directly allow plastics to be sorted among themselves, but which nevertheless allows metal elements to be removed from the waste. It is a method that acts upstream of the actual sorting and is widely used industrially.

Now that we have seen the main types of plastic and the different methods used to separate them, we can now look how to recycle it, and how to apply it on a small scale as in the case of the Tri-Haut project.


[1] https://www.paprec.com/fr/comprendre-le-recyclage/tout-savoir-sur-les-matieres-recyclables/plastiques/le-tri-du-plastique/ 

[2] RECORD, Etat de l’art concernant les méthodes de tri des matières plastiques, 1998, 223 p, n°96-0901/1A.

[3] https://www.boedeker.com/Technical-Resources/Technical-Library/Plastic-Identification

Plastic in all its forms

Posted on July 31th, 2022 by Nathan Lioret

In this article, we will see more precisely what plastic is, how it is made and in what forms it is most commonly found. Indeed, our project essentially concerns the recycling of plastic wastes, and this recycling is not carried out in the same way depending on the type of plastic with which we are dealing. This is why it was essential for us to learn more about the most common plastics and how to recognize them.

What is a plastic ?

Above all, how do we obtain this material that is essential to our modern societies ? The term “plastic materials” refers to polymers, an ordered set of monomers obtained by the cracking (heating then sudden cooling) of naphtha, a liquid resulting from petroleum refining. These monomers are then brought together to form macromolecular chains, i.e. molecules of a sufficient size to be visible by human eye, this is a polymer, which generally takes the form of a little ball (granule) that we will be able to shape afterwards. This polymerization is carried out by using additives (reagents and catalysts) as well as by acting on the temperature and the pressure applied to the monomers. [1] Then comes the last step, shaping, which consists of transforming these plastic flakes into objects. For this, many methods exist, to name only the main ones, here are some examples [2]:

  • Injection molding : the plastic flakes are heated and softened before being sent under pressure into a closed mold using an injection molding machine. This mold gives the shape of the part that will be obtained once cooled. This process is used for objects of all sizes, from plastic bottle caps to garden tables.
  • Injection-blow molding : by combining the principle of injection molding with an air jet allowing the injected plastic to be pressed against the walls of the mould, we obtain the plastic bottles that we know only too well. This is the principle of injection-blow molding.
  • Extrusion : consists in compressing the softened plastic flakes through a mold which will give it the desired shape, whether it is a simple wire, a hollow tube (PVC pipes), complex shapes… We can compare this method to the one used to make churros. Variants exist, such as extrusion-blow molding and extrusion-inflation.
  • Rotational molding : consists in rotating a mold filled with liquefied plastic on itself, then cooling it to obtain the desired shape.
  • Thermoforming : a plastic sheet is softened (it is rolled up if the thickness is small, which is the most common) by heating it before compressing it between two molds which gives it its final shape.
  • Rolling : makes it possible to obtain plates or plastic film by passing the material between two rotating cylinders more or less far from one another (rolling mills).

All the same plastics ?

That would be too easy !

We can already start by differentiating plastics into 2 main categories : thermoplastics and thermosets. Thermoplastics can be remelted indefinitely, which makes them very suitable for recycling, unlike thermosets, which cannot be remelted and are very difficult, if not impossible, to recycle [3]. Fortunately, 80% of the plastic produced in the world are thermoplastics. Also, the methods described above for shaping plastic essentially concern thermoplastics, thermosets being manufactured with more complex methods.

Thermoplastics are once again subdivided into 7 categories, whose properties differ and which are not recycled in the same way, as we will see in a future article [4,5] :

  • Polyethylene Terephthalate (PET) :
    • Properties : light, rigid or semi-rigid, transparent or semi-opaque
    • Advantages : light, solid (impact resistant), impermeable to oxides (CO2) and water, good electrical properties, long service life
    • Disadvantages : high shrinkage during molding, degrades when heated 
    • Hazards : toxic fumes
    • Typical uses : all plastic bottles, food packaging, credit and loyalty cards, stuffed animals and cushions, combs, certain bags, carpets, ropes, etc.
  • High Density Polyethylene (HDPE) :
    • Properties : soft and flexible, high tensile strength, translucent, waxy texture, inert
    • Advantages : thermally stable (resistant to both cold and heat), cheap, good chemical resistance, good electrical properties, resistance to friction
    • Disadvantages : poor resistance to oxidizing agents, less rigid than PP, easy to burn, low UV resistance, high molding shrinkage
    • Dangers : no danger to burn it in itself but the additives can present some
    • Typical uses : pipes, toys, bowls, plastic crates, packaging film, household products, milk bottles, shampoo and medicine bottles, pop caps
  • Polyvinyl chloride (PVC) :
    • Properties : insulating, chemically inert, rigid or flexible, opaque or transparent, non-slip or smooth
    • Advantages : easy to maintain, cheap, resistant to water, fire, acid and alkali
    • Disadvantages : degradation by overheating, brittle below 0°C, discolors if exposed to too much UV, high density
    • Dangers : generates HCL and dioxins when burned (very toxic)
    • Typical uses : Rigid = plumbing pipes, building materials, soles, heat shrink tubing, kitchen utensil handles, patio furniture; soft = cheese and meat wraps, tape, faux leather, gasket, cable sheath, diaper
  • Low Density Polyethylene (LDPE) :
    • Properties : chemically inert, flexible, translucent, insulating
    • Advantages : inexpensive, cold-resistant, resistant to chemicals and hydrolysis, good impact resistance, easy to manufacture
    • Disadvantages : low tensile strength, not very rigid, poor heat resistance, burns easily, poor UV resistance, high molding shrinkage
    • Dangers : no danger to burn it in itself but the additives can present some
    • Typical uses : alimentary film, garbage bags, plastic bags, milk bottle caps, ice cube bags, leaves, plastic bowls, pipes, etc.
  • Polypropylene(PP) :
    • Properties : translucent to opaque, hard to semi-rigid, hydrophobic
    • Advantages : resistant to high and low temperatures, very rigid, very strong, very resistant to abrasion, good mechanical, thermal and electrical properties
    • Disadvantages : more expensive than PE, brittle below 0°C, high gas permeability, low resistance to fuels, low UV resistance, continues to burn
    • Dangers : no danger to burn it in itself but the additives can present some
    • Typical uses : construction plastic, pipes, toys, plastic chairs, kitchen utensils (children’s dishes, microwaveable dishes, drinking straws), butter wrappers, synthetic mats, DVD box, ropes, nets
  • Polystyrene (PS) :
    • Properties : hard, rigid, opaque or transparent, shiny
    • Advantages : cheap, low molding shrinkage, good insulation, good at low temperatures
    • Disadvantages : brittle, low wear resistance, low chemical resistance
    • Dangers : releases styrene when burned (toxic)
    • Typical uses : toys, CD boxes, light diffusers, electrical boxes, cutlery, school materials (square, ruler, protractor), pot of yogurt and fresh cream, styrofoam meat tray
  • Others (OTHER) :
    • Properties : vary a lot from one plastic to another
    • Advantages : very interesting plastics in this category (ABS, PLA, Nylon)
    • Disadvantages : difficult to identify
    • Dangers : difficult to find the melting temperature, we usually end up burning them, so not very safe (some of these plastics give off very harmful fumes, like PC)
    • Typical uses : PC = CD & DVD; PLA = bioplastics; ABS = filament from 3D printers, toys, electronic products; PMMA = acrylic glass; carboys for water cooler, reusable bottles, baby bottles


[1] https://www.paprec.com/fr/comprendre-le-recyclage/tout-savoir-sur-les-matieres-recyclables/plastiques/la-fabrication-du-plastique-l-extraction-des-matieres-premieres/

[2] https://www.paprec.com/fr/comprendre-le-recyclage/tout-savoir-sur-les-matieres-recyclables/plastiques/la-mise-en-oeuvre-des-matieres-plastiques/

[3] https://www.paprec.com/fr/comprendre-le-recyclage/tout-savoir-sur-les-matieres-recyclables/plastiques/la-classification-des-types-de-matieres-plastiques/

[4] https://www.paprec.com/fr/comprendre-le-recyclage/tout-savoir-sur-les-matieres-recyclables/plastiques/

[5] https://community.preciousplastic.com/academy/plastic/basics

Plastic processing around the world

Plastic processing around the world

Posted on 01/12/2021 by Valentin GIRARD

In our previous article, Valentin presented incineration, a technical waste management process for treating waste that cannot be recovered by other means of recycling or recovery.

Finding solutions to deal with the accumulation of plastic waste is becoming essential. It is estimated that 8 million tons of plastic end up in the ocean each year, leading it to contain 150 million tons today. Doesn’t the weather look great for a beach vacation will you tell me ? The problem is not there. It goes much further : plastic breaks down into small particles called “microplastics”. These microplastics are toxic. On the one hand, this causes contamination of drinking water supplies upstream from the ocean. Then, living organisms in the ocean are victims of this contamination. The resulting loss of marine biodiversity causes imbalances, which causes a collapse in marine biomass. This collapse also has a direct impact on continental territories, for many reasons related to global ecosystem mechanisms. To name just one : the effect on plankton. 70% of absorbed greenhouse gases end up in the ocean thanks to plankton. If its biomass collapses, the amount of greenhouse gases absorbed would fall drastically, thus causing an acceleration of global warming, of which we already know some disastrous consequences (more regular and intense natural disasters, rising sea levels and many others).

Hoping to have convinced you that plastic is not a good thing for the planet (and hoping to have given you some new arguments to convince the skeptics around you), let me now take stock with you of what is currently done about the treatment of these plastic wastes on a planetary scale, while explaining to you how our project is positioned in this spectrum of solutions.

Methods to tackle plastic pollution can be divided into 5 major parts, ranked in the figure above from “worst” to “best”. I suggest that you analyze with me each of these methods in the order mentioned.

1- Burial / Burning / Accumulation

Principle : The principle of this method is to get rid of these waste either by piling it up, burying it, or burning it. For the accumulation, we speak of an open landfill. This is often done near the site of consumption, but you should know that many northern countries (including France !!) export their waste to southern countries, Africa or Asia, to landfill them. . Burial, meanwhile, can sometimes be framed with large means, for example nuclear waste which are buried in fairly substantial concrete structures (we go a little outside the framework of plastic but it can also exist for this type of waste). It can also be a simple hole dug and covered. Finally, for burning, the primary goal is to drastically reduce the volume of waste by incinerating it.

Geographic scale : These methods unfortunately have the distinction of being the most widespread. They are widely applied in southern countries, but not only (hello China). The majority of plastics are buried or burned on a small scale (home, neighborhood, even small village). For the large scale, we most often find large landfills, or large-scale landfilling.

Advantages : These methods do not have many ecological advantages, the advantage is economic and logistical. Indeed, it is very easy to practice these methods, and it remains less expensive than recycling for example.

Disadvantages : These methods are very harmful to the environment for several reasons :


  • Open air burning leads on the one hand to a conversion of plastic into water but also into CO2 which is a greenhouse gas, but also has the unfortunate tendency to produce Nox, furans and other dioxins which are very toxic gases. . All the additives and substances contained in the plastics are also released into the air (Mercury and arsenic to name but a few). We therefore have both an amplification of the greenhouse effect and disastrous health consequences (1 death in 5 in the world is due to air pollution according to a study proposed by Harvard).
  • Burial and accumulation causes plastics to degrade into microplastics and contaminate soils and oceans with the consequences seen in the introduction. Another consequence not mentioned in the introduction is the contamination of soil and water by the additives contained in the plastic (see the section on burning).

Comment : In some parts of the world such as Nepal, a popular method is to dump your waste in nature, but not in a wild dump (directly in the torrent for example). This practice is even worse because the degradation of the plastic is then done more quickly and in a less controlled way.

A factor influencing the wide use of these methods (in addition to its low cost and simplicity) is awareness. Taking the example of Nepal again, we went to some villages where the inhabitants are not really aware of the consequences mentioned above. These people, from my point of view, would gladly adapt their practices if awareness campaigns were put in place (and also some rudimentary means provided).

Link to the project : In the Khumbu region, the most common practice is to accumulate waste in pits (around 80 pits in the valley), and then burn the waste with kerosene. It is this practice that we are trying to eradicate with our project.

2- Energy recovery

Principle : The purpose of this practice is to transform waste into energy for useful use. The most common method for this category is waste incineration. The goal is then to produce thermal energy : i.e. hot water or steam. But there are also other methods, for example to generate electricity. Anaerobic digestion (applicable to biodegradable waste, not plastic) or pyrolysis can produce biogas and fuel oil respectively. These two methods can be classified as between energy recovery and recycling.

Geographic scale : Energy recovery is extremely common in developed countries, especially with incineration. When our garbage are picked up, we send a good part of these to the incineration plant, which generally supplies a district with heating. Anaerobic digestion is also beginning to develop on a larger scale, but remains fairly minor. As for the methods of producing electricity or fuel oil, they currently only exist on an experimental scale.

Advantages : The main advantage is that this method makes it possible to see plastic no longer as a burden but as a resource, and this motivates to better manage waste locally. We create wealth with waste, therefore jobs, energy, in short economic and social development. In addition, these infrastructures often need to be on a fairly large scale (at least a district) to be profitable. This requires large investments. Negative point ? Perhaps not if we consider that these large investments are made by influential players who will take care to put in place good security measures for these machines (I am thinking of anti-pollution filters in particular).

Cons : Whether we speek of incineration, biogas or fuel oil, there is always something burning. This produces CO2 which is a greenhouse gas. There is a drawback seen above. However, this often avoids burning an auxiliary fossil fuel. For example, the fuel oil produced by pyrolysis replaces that which would have been purchased otherwise. Or the heating produced by incineration avoids burning wood or fuel oil to heat your home, …

Another disadvantage remains the toxic products. Even if the anti-pollution filters prevent them from ending up in the atmosphere, they form what is called refiom, a very toxic powder that is very hard to process.

Déchets : une étude mesure la part renouvelable de l'énergie produite par  les incinérateurs

Finally, since these infrastructures are on a large scale, they are expensive and require large logistical and financial resources for their use and for the collection of waste, and this prevents its development in the Southern countries.

Comment : A challenge for our century is to develop these methods of waste treatment (as well as recycling) in the Southern countries for non-recyclable waste, because although they remain low in the qualitative scale, they represent very important development compary to burning, burial and accumulation methods.

Other energy recovery methods exist, but remain on an experimental scale. The same goes for recycling.

Link to the project : One of the machines we will bring to the Khumbu region is a pyrolysis system. This solution is particularly suitable for this region because it makes it possible to process a quantity of plastic adapted to the waste production there, and brings added value to the inhabitants, who currently have to import their fuel oil by helicopter from the capital (in this region, a lot of kerosene is used for heating and cooking). This avoids many helicopter flights : a plus for the planet and for the bill of the locals.

3- Recycling

Principle : We all have a more or less clear idea of what it is. According to the dictionnary : “A set of techniques aiming to recover waste and reintroduce it into the production cycle from which it comes”. For plastic, the most popular methods are based on the following principle :

  • For PET (e.g. plastic bottles), it is often transformed into fibers, to make clothes, carpets, sleeping bags, etc..
  • For other plastics (notably PP and PE), they are melted and remolded to make new objects.
The range of Precious Plastic machines (top) and examples of produced... |  Download Scientific Diagram

These methods are often economically viable on a large scale, but some initiatives manage to make smaller machines for more local uses, for example Precious Plastic.

Comment : Plastic is not infinitely recyclable… Much of it is lost as the recycling process causes the plastic to lose its useful properties.

Apart from plastic, recycling works for paper and cardboard, glass (which recycles very well), metals, electronic waste, and even green waste if we consider compost as recycling (recovery as fertilizer). There are also initiatives on a smaller scale, such as the company Fabrick, which offers thermal insulation bricks made from clothing.

Geographical scale : Again, recycling remains marginal in southern countries due to lack of means, but is very widespread in northern countries.

Advantages : Here, we do not produce (a lot of) greenhouse gases, and we avoid producing plastic from oil.

Disadvantages : The main disadvantage is that this method encourages (especially Westerners) to consume plastic. For lack of information, many see plastic as the miracle method. Once in the yellow bin, this plastic will be used again, so we have a clear conscience. But plastic is not infinitely recyclable, and recycling it still requires a lot of energy, and generates pollution.

In addition to this, due to the size of the infrastructures, for the same reasons as energy recovery, these technologies are struggling to develop in southern countries.

Link to the project : The problem with the pyrolysis machine is that it does not process PET. We will be inspired by the machines offered by Precious Plastic to provide a second machine capable of transforming PET into a useful object for the inhabitants of Pangboche and the surrounding villages.

4- Re-employment

Principle : The principle is to find a second use, or another user for a plastic product that we no longer use. Transforming a plastic bottle into a wasp catcher, audio discs to scare away birds, reselling your coffee maker on Leboncoin or giving your cousin your undersized clothes, we have all already experienced it… But do we do it enough ?

Geographic scale : This practice exists all over the world because it costs nothing and is easy to implement. But it is (I think) less well applied in Western countries, because it is even easier to throw away your waste.

Advantages : This method avoids consuming plastic from petroleum manufacturing, or recycling. 100% of the product is reused, there is no loss here and no large carbon emissions.

To go further, thinking about reusing allows you to change your mentality with regard to plastic. This promotes the circular and local economy. Reuse is the archetype of sustainable development :

  • It avoids plastic pollution and the carbon emissions associated with it
  • It creates links at the local level (resale of goods, DIY workshops, etc.)
  • It saves money on expenses

Disadvantages : It is not feasible on a large scale, and only applies to certain rather specific wastes. For example, it is difficult to apply this to plastic packaging.

A second small drawback is that it can overshadow the next category a bit.

5- Reduction to the source

Principle : All of the above methods, although some are more acceptable than others, are based on the principle of plastic consumption. But given that oil is a fossil resource, and that most plastic ends up in the oceans, the best thing is to limit its consumption. There are many ways to do this : buy your products in bulk, use metal or wooden products rather than plastic (cutlery, bottles, etc.), etc. There is already enough content on this subject on the internet.

Geographic scale : This method applies everywhere, but is much more prevalent in developing countries. This time it is the Westerners who are showing the bad example, by consuming much more than the Southern countries. But unfortunately, overall, this often remains a sudden phenomenon (due to a lack of financial means, for example), rather than a well-considered choice.

Advantages : This principle allows to reduce one’s carbon footprint, because it is not necessary to resort to the previous methods. It also allows you to save a lot of money.

Disadvantages : An a priori undesirable consequence that one could evoke would be the decline in economic activity. But we know very well that GDP is well correlated with carbon emissions. Real downside ? I don’t think so… On the other hand, this raises systemic questions : the decline in growth or decline must be accompanied by public aid for the reconversion of jobs in carbon-intensive sectors towards professions in the sectors most in harmony with a world more sober.

Link with the project : During the 3rd phase of the project (sustainability phase), we would like to carry out an awareness-raising action for the locals but also and especially for tourists, to encourage them to reduce the amount of plastic in Khumbu, and so that the remaining waste is brought down to the Kathmandu valley as much as possible.

Perhaps there is no great conclusion to be drawn from this observation, it is indeed an overview of the current global situation of the treatment of plastic waste.

However, there is a major trend : due to a lack of means, the countries of the South have difficulty in procuring large waste treatment infrastructures, because they are expensive and require large logistical means that are sometimes complicated to set up in these countries. In a village where there is no road access, the garbage truck struggles to pass every week…

I was talking earlier about the challenge of this century to bring these great structures to these countries. Perhaps the solution would rather be to find solutions adapted to these countries : recycling on a smaller scale. This would allow southern countries to have easier access to recycling.

Another finding is to see that Western countries globally prioritize energy recovery while less developed countries prioritize burning and landfilling. Awareness and information remain the only way to change mentalities and move the world to reuse and plastic sobriety, hence this article… To think about, to share !

The pyrolysis

The pyrolysis

Posted on 18/10/2023 by Pierre Jaraud

The principle of plastic pyrolysis

The aim of this article is to explain how a plastic pyrolysis machine works, and why it’s so useful. It also explains the difficulties that Tri-Haut has faced in implementing pyrolysis as part of its plastic waste treatment solution. 

Plastics pyrolysis uses the reverse process used in the plastics industry: its aim is to break up chains of molecules – known as polymers – by cracking, in order to return them to a state close to their initial state. This is how liquid and gaseous hydrocarbons are obtained at the end of the process.

Before starting the pyrolysis cycle, waste preparation is essential. Plastics of the PE and PP types are sorted out, as they are the only ones suitable for the process. This is followed by washing with water and drying to obtain the best possible quality products. Finally, the plastics are shredded to accelerate thermal degradation in the reactor.

Prolysis involves initiating oxygen-free combustion in the reactor (P). This is achieved by heating the reactor to a temperature close to 450°, as our pyrolysis is categorized as low-temperature. The plastic will rise in temperature in the reactor, until it reaches its melting point. After melting, the plastic will continue to rise in temperature and finally begin to vaporize. The plastic in the form of gaseous vapour passes through the pipes connecting the reactor to the condensers (C1). These pipes act as a cooling system, enabling liquefaction to take place. The liquid phase is then collected in the various condensers, depending on the temperature of the different products.

Illustration du procédé pyrolytique

At the end of the pyrolysis cycle, two types of products are recovered:

  • Fuel oil. In the various condensers, the liquid phase, also known as “pyrolysis oil”, is collected during the cycle. It is directly flammable, even if its quality requires pre-combustion or flue gas treatment.
  • Gas. The gas phase has not fully condensed and can be recovered downstream of the plant. A storage system (gasometer) is usually used.

However, the process also produces two types of waste:

  • Wax. This is the solidified form of pyrolysis oils, visually similar to a paste. It is not easily flammable, and its production is highly likely to clog the machine and lead to its breakdown.
  • Coal. This is the ultimate waste product. In concrete terms, it’s a kind of burnt dust, which concentrates all the elements and additives in the plastic that can’t burn. This waste is very difficult to recycle.

Tri-Haut’s work on pyrolysis

Tri-Haut’s approach to plastic pyrolysis was initially empirical. Right from the year the association was founded, a team worked on the subject with the aim of building a pyrolysis plant in Nepal. To fully understand the stakes involved in such a project, we need to take a closer look at the conditions under which the machine would be set up.

The pyrolysis machine is intended to operate in Pangboche, a remote village 4000 m above sea level in the Everest valley. The machine will be operated by a local operator trained by the association, not an expert in industrial processes. Having these constraints in mind is important for understanding the Tri-Haut approach.

After deciding to abandon work on the incinerator (see related article), the first team turned their attention to pyrolysis for the added value it could extract from plastic waste. Time-pressed, they adopted an empirical approach, building a prototype in Kathmandu.
This prototype, with a capacity of 5 litres, was built in a factory with limited technical resources, compared with what is done in France, for example. The idea was to build the pyrolysis system on site, so as to be able to find the materials needed to repair it.
This first team carried out a battery of tests to study the influence of various parameters on product quality and quantity. These included: final heating temperature, type of plastic, quality of plastic preparation, etc. This test phase also highlighted a number of areas of concern and difficulty, such as leakage zones and conditions leading to machine clogging.

A year later, the second team was able to carry out further tests on the same prototype, with different objectives. The influence of the length of the cooling pipe and the types of plastics processed were studied.

However, it was the third team that decided to make pyrolysis its priority from the end of 2022, with the aim of building the final version in Nepal during 2024. To compensate for the lack of knowledge highlighted, and to complement the results obtained during the two years of experimentation, a theoretical approach was favored.
Over a period of several months, the Tri-Haut team synthesized the state of the art and made numerous contacts with professionals in the field, in order to increase its expertise in the subject. The actual dimensioning work began, and despite the numerous aids provided by experts in the field, the work proved tedious.

With hindsight, this can be explained in several ways:

  • Pyrolysis is a relatively young and not yet mature technology. Its use in industry is mainly oriented towards biomass pyrolysis, so resources on plastic pyrolysis are rare.
  • The team were novices in the field, and had to learn on the job on their own.
  • The desire to focus development on low-tech added further constraints, which were not mastered by the companies in the sector who were asked to help with development. Indeed, Tri-Haut pyrolysis differs in many respects from the pyrolysis processes developed in industry.

Despite these difficulties, Tri-Haut’s work resulted in an almost complete dimensioning of the pyrolysis system. This meant that only a few details remained to be ironed out, and the equipment list could be sent to Nepal to prepare for the team’s arrival.

Reasons for stopping development

However, during an exchange with Earthwake’s R&D team and management, Tri-Haut was warned about the feasibility of its pyrolysis project.

A number of comments were made, which are summarized below:

  • Despite all our efforts, the fuel obtained will be of poor quality, so that it cannot be burned in an engine, at the risk of clogging it and leading to its destruction. What’s more, burning it by any means releases toxic fumes that require extensive treatment at every point of combustion.
  • The extraction of these pyrolysis oils remains dangerous, as the slightest imperfection in the process leads to the formation of gasoline vapors with a high flammability potential.
  • Cleaning the tank at the end of the cycle to remove the carbon requires the use of tools. Even the slightest spark can cause an explosion, as dense, flammable gases stagnate at the bottom of the tank.
  • It is not possible to ensure the absence of oxygen in the pipes. This poses risks of auto-ignition, particularly at the beginning and end of the cycle. The only way to inert the pyrolysis is by injecting nitrogen, but this solution is not feasible in the geographical context of the project.
  • Pressurizing the pyrolysis gas requires very expensive ATEX compressors. If non-standard compressors are used, there is a risk of explosion. Gas at too low a pressure burns poorly and risks fouling the boiler.


In short, Tri-Haut was confronted with the risks posed by low-tech pyrolysis, which is far less safe than the industrial models that served as inspiration. These risks are not only limited to potential material damage, but can also endanger people’s health. With 10 years’ experience in the field, it would have been irresponsible and presumptuous to ignore Earthwake’s warnings. Not wishing to endanger the health of the sorting center’s staff or its members, Tri-Haut took the difficult decision to suspend the development of pyrolysis.
However, the work carried out is not lost, as it will be passed on to Madindra, a Nepalese engineer wishing to develop this technology in Kathmandu, in a more suitable context.

The incinerator

The incinerator in 2 minutes

Posted on 27/12/2020 by Valentin Girard

So what we are going to do is that we will first explain to you how an industrial incinerator works, and then why we will have to adapt ours and how. Okay with you ? Here we go.

A short video is better than a long speech, right ? We found a super well done one for 1 minute 15 (in French) :

For those who were lazy, here is a little recap in pictures

Schéma d’un incinérateur
  • The waste is pre-sorted. Excessive waste and large metal waste are discarded.
  • The rest goes into the storage pit. A clamp supplies the combustion chamber.
  • The combustion chamber has previously been heated with town gas, and is always maintained above 850°C for complete and clean combustion of the waste.
  • What has not burned is called clinker. It is composed of ashes and metals. They are stored, and can be reused to stabilize land for example.
  • The fumes are very hot. This heat is often used to make electricity with advanced steam engines, and/or to heat water for the city’s heating network.
  • The fumes are filtered with lime and coke to pollute the atmosphere as little as possible. What is recovered is called the refiom. This powder is very toxic to the environment. It must be treated with great care.
  • The rest of the fumes are evacuated by high cooling chimneys.
  • If the combustion chamber must be stopped, it must be done gradually so as not to produce too much smoke and solid waste.

Sounds easy on paper, right ? But hey, you can imagine, we won’t be able to make an industrial incinerator at 4000m. This would be well above our budget, but also unsuitable for the terrain, and the amount of waste to be incinerated. We have another problem : the environmental conditions. This puts a spoke in our wheel for 3 main reasons :

  1. Firstly, there is less oxygen at this altitude. And lack of luck, it is very important for the combustion. It will be necessary to bring more air inside the combustion chamber to have enough oxygen.
  2. But that poses a second problem : it’s freezing in the mountains. And you remember, we said above that the combustion chamber must be at least 850°C to ensure good combustion, which does not pollute too much. Not easy if you bring in a lot of cold air, and the walls of the incinerator are cold.
  3. Finally, in Nepal, and in addition at 4000m altitude, it is impossible to imagine someone picking up bottom ash and refiom, and treating them in good conditions. A solution will have to be found.

So what are we going to do ? Or at least what would we like to do ? Well, a bit like an industrial incinerator, but integrating low-tech technologies, and smaller. We have a little less than a year to design an incinerator which :

  • Burns all non-metallic waste that would end up in the rivers else.
  • Limit air pollution.
  • Recycles waste by producing electricity and/or hot water.
  • Is the easiest to manage for local people.
  • Can be installed at altitude, and which adapts to the climatic conditions of Khumbu.
  • Produce as little residue as possible (bottom ash and refiom).

To help us integrate all this, we benefit from the work carried out by the Falchen Kangri association. It is an association of INSA Lyon which went to install an incinerator in the Himalayas at an altitude of 5000m.

It is therefore a great challenge that is offered to us today.

But we accept this challenge with open arms, and we are sure that with our motivation and your support, we can do it !