New technology increases phosphorus recovery from sewage sludge

With the threat of phosphorus deficiency before our eyes, Ragn-Sells AB, Easy Mining Sweden AB and a researcher at the Swedish University of Agricultural Sciences, have proven through new technology that it is possible to extract phosphorus from sewage sludge with low quality.

– Now we are planning for a large-scale production plant, says Anders Kihl, Development Manager in Ragn-Sells, in an interview on

In the last decades the environmental threats has increased, as has the knowledge of our resources’ finitness. Many companies have gone from thinking traditional linear economy, from raw material to product to waste, to circular economy, recycling and new business models where you want to minimize the waste and transform it into new raw materials. Products are designed so that they can easily be recycled.

Low quality sewage sludge is a source of phosphorus

Ragn-Sells is one of the companies that has adopted the new economic world order. Together with Easy Mining Sweden and Dr Yariv Cohen at the Swedish University of Agricultural Sciences they have proved in a project that it is possible to extract phosphorus in a cost effective manner from sewage sludge with low quality.

– We want to close the loop between country and city, and the new method is based on sewage sludge being incinerated along with recycled wood chips. From the ashes we can extract different phosphorus compounds, Anders Kihl explains.

Ragn-Sells handles the main part of the phosphorus-rich sewage sludge being spread on our fields. The sludge that the company returns to agriculture is of high quality and approved for distribution. But the company has noticed an untapped phosphorus availability: the sewage sludge with low quality which is also produced at our sewage treatment plants. The sludge may contain high levels of heavy metals that are not suitable for returning to fields.

– In such cases only sludge incineration remains, and if you don’t take advantage of the phosphorus from the ashes, it will disappear out of circulation, says Anders Kihl.

Adding wood chips in burning

Anders Kihl says that it is Dr. Yariv Cohen who has developed the innovative method for the phosphorus and other substances to be separated from the ash, sewage fractions and mining waste. The ash is dissolved in sulfuric acid and by chemical methods iron, aluminum, heavy metals, gypsum and phosphorus will precipitate from the solution. Phosphorus is then extracted as ammonium phosphate and calcium phosphate.

– Together with Easy Mining Sweden, we have demonstrated that it is possible to burn sewage sludge, even with low quality, along with wood chips and take care of the phosphorus. Without it becoming odor problems, says Anders Kihl.

– In addition, the combustion destroys the contaminants, toxic substances and drug residues. All heavy metals are collected and deposited in modern and safe landfills, as well as the energy of the sludge recovered through the incineration.

Large scale production plant are being planned

Ragn-Sells is now planning a large-scale production plant to exploit the untapped resource, and in the plant process some 30 000 tons of ash per year.

– For the process to be profitable, the phosphorus content needs to be about 5 percent in the ash, and we have that now. We hope that future rules and regulations in the area will be designed to demand phosphorus extraction in sludge incineration. Without clear national guidelines there is a significant risk that the sludge is incinerated without any phosphorus being recovered, concludes Anders Kihl.

Facts about "peak phosphorus"

Access to phosphorus is a precondition for global food production. Nearly 90 percent of the phosphorus that is extracted is used in fertilizers, animal feeds and pesticides. But phosphorus is becoming a global shortage and the concept of "peak phosphorus" is a reality, as the demand for phosphorus is greater than the supply. Calculations show that the peak phosphorus may occur within approximately 80 years, and that the total recoverable reserves will run out in about 350 years.

Facts about Ragn-Sells

Ragn-Sells AB is a family company and a business group, operating in Sweden, Norway, Denmark, Estonia, Poland and Latvia. The company has worked with recycling in various forms for over 40 years. Some of the company’s expertise areas are collection, clean up and disposal of household waste, as well as commercial waste, hazardous waste and contaminated soils.

The Group has approximately 2,500 employees and sales of around 4.5 billion per year.

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