Recycling Plastic Waste

Perjantai 14.10.2022 klo 15.16 - Nikk Nikinmaa

One of the biggest problems with recycling plastic waste has been that a mixture of different plastics cannot be used as a feedstock for generating new plastic products. This means that either the consumers have to be quite careful and knowledgeable in sorting plastics or recycling stations need to carry out expensive sorting of plastics for further use. In a recent article in Science (October 13, 2022; DOI: 10.1126/science.abo4626) Sullivan et al. present a method that can be used for a mixture of plastics to generate starting material for commercial use. The method is comprised of two steps: first oxidizing the plastic mixture with metal-based catalysis (Co and Mn) to intermediates that can be digested by engineered bacteria to produce a feedstock for new commercial products. By varying the way that the bacteria are engineered, different starting products can be generated.

To my eyes, this method is quite safe and practical. It avoids the inherent problem with plastic-eating bacteria. I remember the book Mutant 59 by Kid Pedler and Gerry Davis (from 1971) where the plastic waste was planned to be eaten by bacterial mutation, which was very effective in consuming plastics, favoring them over any other foodstuff. The mutant naturally got accidentally free and started devouring everything made of plastics. Planes started crashing down, because all the plastics covering electric leads were eaten up and motors short-circuited. Most things in our houses became non-functional or half-disappeared etc., naturally, if you look around: most things are at least partly made of plastics. Since in the method described by Sullivan et al. the engineered bacteria eat only the oxidized end product of catalysis, they can only live in the recycling plant. By combining this method with effective collection of plastic waste, much of the plastics problem can be removed.

However, even if we get smokers to put their cigarette butts to waste bins, there will be one significant source of small plastic particles. Almost half of the microplastics in the environment is tire wear particles. They are impossible to collect. Thus, even if the recycling of all other plastics were more than 90% successful, this source would remain. It can only be reduced by drastically reducing road traffic. In this regard, electric cars are not a solution, the only solution could be using rail traffic and public transport more generally.  

Plastics - not an environmental problem as the material but because of consumption habits and waste management

Perjantai 8.7.2022 klo 19.16 - Mikko Nikinmaa

After plastics were invented, they started appearing everywhere from packaging to toys. One can say that since 1970’s we have lived in plastic age. Pretty much everything has been made of plastics or wrapped in plastics. For years we have carried our shopping home in plastic bags, drunk from plastic bottles and used plastic single-use utensils.

A few years back one started noticing the huge amount of plastic waste accumulating in the environment. As the extreme huge plastic gyres have formed in world’s oceans, the Pacific as the worst example. We have all seen pictures of birds and fish getting stuck in plastic bags or fishing gear, and microplastics are found in every aquatic environment. As a result, a movement considering plastics as one of the most important environmental problems has emerged. However, stating that plastics are bad and should be banned does not address the real problems, overconsumption, cost minimization and waste management problems.

Plastics as materials are cheap, durable, malleable, inert and recyclable. Those properties make them ideal for many uses, and are the reason for plastic age. For example, the Lego bricks, which I got 60 years ago have not aged at all. Indeed, it is estimated that no aging occurs for at least 500 years. This durability is invariably said to be a problem, but I would say it is a good thing. In the following, I go through the questions associated with plastics and point out which changes and solutions would be available to us.

Traditionally plastics are made of oil. As our dependency from fossil fuels must be decreased, this requires that oil-based plastic making is reduced and finally stopped. However, since the material is durable, even oil-based plastics have small carbon footprints. Exactly the same plastics can be made using, e.g., wood as starting material: they look the same, are equally durable, and cause similar contamination if thrown in the environment. However, since they are not made from oil, their carbon footprint is smaller than that of oil-based plastics.

The real reason why plastics have become an environmental problem is our overconsumption. As a consequence, plastics, being very cheap, have been added as wrapping materials to everything. Extreme examples are biscuit boxes, which are enclosed in plastic and each individual biscuit is also enclosed in plastic: wouldn’t a single cardboard casing suffice? We have taken plastic bags for granted. Since we consume a lot, every time we go to buy clothes, a lot of plastics follows home with the shopping. If the use of unnecessary plastic were discontinued, a large portion of plastic contamination would disappear.

Much of the plastic is recyclable. Although this is the case, the efficiency of recycling is not more than 50 % even in the best countries. This is far from the 95 % efficiency of glass bottle recycling in Finland. If the efficiency of recycling were improved, plastic pollution would be much decreased. In waste collection, many companies are saving money by transporting plastic waste to poor countries for nominal fee. As a result, plastic contamination in rich countries disappears. However, the treatment of plastic waste in most poor countries is to throw it in the rivers where the float to the oceans, out of sight and out of minds, contributing to the garbage gyres of the oceans. It would be very simple to stop this kind of “saving”. One could make international agreements that transport of plastic waste across national boundaries was forbidden. Burning plastic waste is a much better alternative than its transport and consecutive appearance in garbage gyres. Plastic burning could substitute the use of fossil fuels for heating.

Today most plastics are nontoxic. Earlier toxic components were much more common. The problem is that plastics are hydrophobic, and most toxicants are also hydrophobic. Because of this microplastics can act as carriers of toxicants into animals in the aquatic environment. The toxicants are taken in together with the microplastics. The most effective way of decreasing such toxic impacts would be to decrease the amount of toxic chemicals, such as insecticides and other pesticides, released in the environment. The two major sources of microplastics in the environment are tyre wear particles and cigarette butts. Both contain a plenty of toxic compounds making the microplastics released quite toxic. The tyre wear particles could be decreased by decreasing car and truck traffic. Thus, exactly the same action would combat microplastic pollution and climate change. With regard to cigarette butts all that would be required would be for smokers to use cigarette trays or waste bins to dispose of the cigarettes, not throw them to the environment.

Thus, all the aspects of plastic pollution are solvable. It is only the matter of actions; one could demand that they are done.