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In theory people can separate waste much better than a machine, since they have more knowledge about the waste itself.

In practice, with all my good will, I find that following the directions for separating is very difficult, since (just one example) paper can be recycled, but not if it is coated, which is not easy to judge sometimes.

Also, many people do not follow the rules, it's life.

Anyway, mechanical separation does exist. While it cannot (I think) surpass manual sorting, it brings reliable results, which it could also be that they surpass not the theoretical, but the actual quality of manual sorting.

My question is: are there studies about the real effectiveness of manual vs mechanical sorting of household waste? I assume in this case only a humid/food vs everything else manual separation, since it's easy enough to do and to understand.

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Where I live we have separate waste streams for things like organic waste, paper, glass, batteries and cloth but for everything else (like plastics, metals, drink cartons, and crisp bags) it's up to each municipality to decide whether people need to separate waste themselves (a.k.a. source separation) or do mechanical separation in a waste processing facility. Most cities here use source separation, but a few larger ones recently opted for mechanical separation.

The big advantage of letting people separate waste at home is that you generally get cleaner plastics and thus a higher quality of recycled plastic. Another advantage is that separating waste requires people to think about their waste and raises awareness how much they generate.

However with source separation, some form of mechanical separation is often still needed. People can be sloppy, or unknowingly throw their waste in the wrong container. Since equipment for mechanical separation is there, it's cheaper to separate all waste mechanically. Also collecting 1 big container is easier, cheaper and requires less space than collecting multiple smaller containers.

It is clear that source separation is best for some materials like organic waste, paper and cloth. If you do not, those types of wastes cannot be recycled properly and become worthless. For the remaining materials there is no clear conclusion. The research (and debate) which approach is best for processing plastics, metals and drink cartons is still ongoing here, but it seems that the effectiveness of each approach differs per municipality.

Sources (in Dutch):

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Yes. I searched for "study consumer recycling separation"

I assume you mean manual sorting by consumers, because an awful lot of recycling is manually sorted in recycling centres. In the worst case things like circuit boards are burned then smelted in terrible conditions by wretchedly poor people to "sort" the valuable metals from the other parts, but almost any recycling centre will have a conveyor belt somewhere with people standing over it picking bits out. The ones that don't typically consume pre-sorted material.

The studies I found are generally comparing consumer sorted vs not, because there will always be a post-consumer sorting stage. Since your question compares "in theory..." I'm going to focus on the "in practice" comparison.

  • as noted in the question, even with the best will in the world there will still need to be a post-consumer separation stage. There will always be mis-sorted and contaminated material in the recycling, even if it's caused by birds pooping on the material as it's being processed (happens!).

  • not all recycleable material is easily categorised. And not all consumers have the proper tools to classify material, especially plastics. But a plastic recycler can justify buying a reflective spectrometer (for example) to better sort some plastics. And not all producers of plastics are honest in their labelling.

  • for practicality/ease of handling it's often necessary or convenient to combine sorted recycling into fewer streams. Ideally this is done with sets than can be trivially separated (think scrap steel + plastic bottles), and it's often done at the customer-sorting stage "plastic and aluminium drink containers".

  • many, many recycleable things are compound objects. At the extreme a smartphone is extremely recycleable, but there are many different materials involved. But even something as simple as glass is generally contaminated with bottle tops (ideally steel, because magnetic separation is easy, but in practice aluminium and plastic are also present).

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The upper echelon of the waste hierarchy is avoidance of products that produce too much waste. As for separation...that's a matter of scale of waste and how much time/effort goes into your routine. Recycling paper is a waste of time. Incineration or composting (if it's doable) is more practical. As for plastic........you can melt down your plastic in the oven or using a simple 30 dollar heat gun. Reduce your trash volume by 90%

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  • 1
    This does not appear to be an answer to the question. – Jean-Paul Calderone Oct 26 at 13:54

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