Turning residual streams into soil

- We compost quite a lot of bio-sludge, so part of it undergoes a shorter treatment process – one week instead of three months, says Marcus Åberg, regional manager at Ragn-Sells Treatment & Detox AB.

Every day, bio-waste is fed into the reactor’s drum from one side, and ready-made composted material is discharged from the other side. The next step is to develop the recipe for the mix of waste put into the drum in order to optimise the process.

- We’re looking at how we can streamline the mixing process using the drum paddles. We’re also investigating how we can streamline material handling both in the process and inside the drum, and in the next step we’ll try to recover the heat from the drum, Åberg says.

Thomas Storsjö, CEO of Biocompost, says that the reactor in Umeå can turn 15–20 cubic metres of sludge from process industries into nutrient-rich soil every day.

- Ragn-Sells composts bio-sludge from SCA’s Obbola paper mill in a full-size facility as an alternative to the older method of putting the compost in large piles, called windrows,” Storsjö says. “A drum is much less soil intensive and you keep more nutrients in the material, mainly nitrogen, while you get less emissions of methane gas.

A boost of soil nutrition

- We believe that bio-sludge from process industries is great for composting and can provide good nutrients to the soil. There are so many different types of industrial waste, so there’s much more to be gained from these residual streams when it comes to soil production, Storsjö says.

Priority projects for RISE Processum’s R&D council

Two R&D activities were selected by the R&D council and are being carried out within IB:ACCELL to drive these developments.

The 2019 R&D activity “Peat replacement through composting” was conducted to demonstrate that bio-sludge was compostable. The following year the launch of a follow-up project, “Bio-sludge as growing media”, which looked at the properties of composted bio-sludge and its potential for use in cultivation soil.

- Through these R&D collaborations, we took major steps to show that materials from process industries are good for composting and can provide good nutrients to the soil.

Huge business potential

The peat used for soil today has good properties in cultivated soil: it retains moisture and binds the soil together. But it is a finite resource. This is why demand is increasing for products that can replace peat, with composted material offering a potential alternative.

Biocompost has also sold a reactor to a soil producer in Lund, where horse manure will be composted to reduce the peat content in soil products. With the drum, the waste from horse farms can be processed and managed in a way that reduces methane gas emissions.

- The purpose of these collaborations is to find alternatives to artificial fertilisers and substitutes for peat,” Storsjö says. “In lots of places in the U.S. and Europe where artificial fertilisation has been used for so many years, soil depletion is a problem. The need for compost soil from recovered materials will increase dramatically in the future.

Read more about the R&D-council