Conversion of waste products creates climate benefits
The project Rest to Best started with Markus Paulsson at Lund Municipality was looking for a technology to care for sewage sludge. It turned out that the pyrolysis method could be a possibility. Pyrolysis is the heating of organic matter in an oxygen-free environment to usually between 500 — 1000 degrees so that the material is broken down into gases (which are burned) and into the solid biochar. In connection with this, the municipality of Lund came into contact with a group that wanted to test different uses for biochar.
- We decided to put our bags together and look at the whole value chain of biochar from raw material to end use, says Markus Paulsson, energy strategist and project manager at Lund Municipality. We applied for Vinnova's call for challenge-driven innovation and received an initial funding.
The Project Travel to the Best started with a preliminary study in 2017, in 2018 it was completed with step 2 and step 3 will run until November 2023. In the project, they wanted to try to make the graphic-like substance biochar from four common residues. It is waste from parks and gardens, sludge from wastewater treatment, clean from seed production and seaweed washed up on beaches.
The materials are handled in a pyrolysis plant where they are heated to high temperatures. In this way, biochar is formed — at the same time that, for example, the heavy metal cadmium evaporates and can be collected in another chamber. This results in a relatively clean product that has proven to have very many uses with very good climate effects. In Rest to Best it has already been seen that it is possible to make biochar from all four residues. What sometimes poses problems is the pretreatment, such as drying the sludge or removing rocks from park waste.
When the project started, there was no possibility of pyrolysis of its own. There are now three facilities in the project; one at Skåneseed in Hammenhøj, a hos VegTech in Vislanda and one on Telge Recycling in Södertälje. During the same period, many new pyrolysis plants have also appeared around Sweden, including in Helsingborg at the city's waste company NSR. Potentially you could have facilities both in municipalities and on larger farms, but it is an expensive investment. The municipality of Lund calculates what it costs to start biochar production, either by itself or together with another partner.
Biochar is a very stable substance that can retain water and make it accessible to the roots of plants. It can also bind nutrients and is an environment conducive to microorganisms. Therefore, it is perfect for everything from green solutions in urban environments to agriculture and horticulture. Since the biochar easily binds various molecules to itself, it is also suitable for water purification.
- Something we have learned is that biochar is not one thing, but there are different qualities with different properties depending on the raw material you have and how you process it, continues Markus Paulsson. There can be large differences in water holding capacity, in the properties of carbon sink, in density and in carbon content. In the third part of the project, we are now trying to match the products so that they are suitable for different applications.
Around Sweden, tests are being conducted on how best to use biochar. Stockholm is far ahead and has a method where biochar is always used for newly planted trees and Malmö has its own soil recipes that should fit particularly well in Malmö's crops. In Lund, they have tested using biochar to make football pitches drought-resistant. A spinoff to the Rest till Bäst project in Lund is that VA SYD has built a test bed in Ellinge for working with sewage sludge. Lund is also testing biochar for solutions in urban environments.
- We have planted rain beds in the plantings on the recently tapered Byggmesteregatan. The idea is for the rain to flow into a planting that can store a lot of water. To create this, we have used biochar macadam, which consists of macadam, biochar and compost. Another good effect is that the water is filtered and purified as it flows through the plant beds.
In addition to all the uses already mentioned, biochar is also carbon dioxide negative. Making biochar is a way of sequestering the carbon that plants have accumulated during their growth. Had the plants been allowed to decay, the carbon would have reverted to carbon dioxide, which is released into the atmosphere, but biochar retains carbon. Biochar has a half-life of 150 — 5000 years — and is therefore very stable. Biochar is therefore considered a climate sink and has since 2018 been classified as a Negative Emission Technology by the IPCC.
How much will Sweden work with biochar in the future?
- I see that the area is still immature, says Markus Paulsson. There are strong developments on the technology side and I hope that can bring prices down. Sweden is far ahead in the use of biochar and we see that production is growing every year by 60 to 80 per cent. One trend is that many large tech companies buy biochar as a carbon sink for climate compensation and that price has gone up. When the price of carbon sink has gone up even more and when the production price has gone down sufficiently, it will lead to a rapid development. This, I believe, will happen in the not too distant future.
What is the most interesting thing you have come up with?
- What I like a lot is that we have a circular system. We recycle materials and obtain a treatment method to create a sought-after material to use in our cities. The result will also be a carbon sink, so there are many advantages of the material. It's great that we can do such a project in Lund. Our vision is that “Lund creates the future — through knowledge, innovation and openness” and this is a good example of that.
Read more
In this article, we only scratch the surface of the rich material that exists about the project Rest to Best and about the work with biochar. The Rest to Best project has a very informative website that explains the whole process from residual product to biochar, about pyrolysis and climate benefits and much more. You will find it here.
The project has developed a manual on biochar and worked to harmonize the European certification and Swedish regulations and laws with each other. Here are handbook.
