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Oskar Öberg, Adam Rönnbäck and Jacob Sundberg Photo: Åsa Stubbfält
Oskar Öberg, Adam Rönnbäck and Jacob Sundberg, three of the students who have studied the strength of the compost bags. Photo: Åsa Stubbfält View original picture , opens in new tab/window

Compost bags that break – here's the explanation

Published: 23 July 2019

Are you one of those who throw your food waste into flammable instead of using compost bag? Have you experienced that the compost bag broke down on the way to the garbage can? Five students at Luleå University of Technology have investigated the factors that make the compost bags not, even though they are made for the purpose.

Norrbotten residents have for ten years used biodegradable compost bags from the supplier BioBag to sort their food waste. Today, about 30 percent of all compostable food waste from households in Norrbotten is mis-sorted, even though the compost bags are distributed free of charge. One of the reasons is that the compost bags can break so that the food waste ends up on the floor.
– It is very common for households to mix the compostable food waste with combustible household waste, which creates great social losses. If everyone were to sort the right, many more buses would be able to go on biogas produced by the food waste, and we would get a more circular sustainable society, says Adam Rönnbäck, a student at the Master Programme in Industrial and Management Engineering, who completed the project together with the students Oskar Öberg, Jacob Sundberg, Peter Andersson and Simon Larsson Turtola.

Examined three factors

In the course "Experimental Planning", five students from the MSc Industrial Economics got the chance to investigate the strength of the compost bags in a collaboration with BDX who buys and manages the compost bags in large parts of Norrbotten.
– Our mission was to investigate and ensure which factors affect the BioBag bag's strength by performing a separate experiment where we examined how three different factors influenced the compost bag's strength: what type of vessel you have the compost bag in, how long the food waste is in the bag and bag design, says Jacob Sundberg.
"We encountered many challenges during the experiment and we had to perform many pilot tests to ensure that our measurement method worked and had high statistical reliability," says Adam Rönnbäck.

The design is important

An underlying explanation for the large proportion of mis-sorted food waste is considered the tendency of the BioBag bags to rupture and break. The bag's ability to break down in a short time also makes it sensitive. How to use the bag in the household is therefore crucial for how well it holds together.
– For example, many households use a closed vessel instead of a ventilated vessel recommended by the supplier. In combination with allowing food waste to remain in the bag for a long time, the strength can be adversely affected so that the bag breaks, says Oskar Öberg.
The study showed that the bag's construction is of great importance for the strength and that a longer time in the vessel has a negative effect on the strength of the bag. The compost bags stored for two days kept better than those stored for five days. The study also showed that the vessel used has a small effect on the strength of the bag, but on the other hand, it is of great importance when it comes to mold and liquid formation and odor. A closed vessel creates much more mold, liquid and odor than a ventilated vessel.

Guidelines for consumers

One challenge was to obtain a large amount of food waste for the experiment. The students turned to Ica Supermarket at Porsön, which sponsored with 100 kg food waste from fruit and vegetables.
The result of the study will form the basis for future guidelines that BDX can convey to consumers regarding handling of the compost bags. The guidelines are expected to provide greater opportunities for Norrbotten's residents to be able to sort and manage food waste without problems and consequently reduce the proportion of mis-sorted waste.
Also, the supplier BioBag, which produces compost bags in large parts of Norrbotten, should look at the results of the study and then review the design of the compost bags to assess whether there is anything they can improve to increase the strength.