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Designing ash for the world’s food and environment

As a rule, farmers are sceptical towards fertiliser that uses slurry from waste treatment plants, even though it is rich in phosphorus – one of the most important nutrients for improving harvests. But what potential does the slurry have if it is incinerated? Anita Pettersson's Researchers’ Grand Prix-winning research is looking for a cost-effective method to create designer ashes that can be spread directly onto fields.

Global stocks of phosphorus for use in mineral fertiliser are running out, some prognoses even suggest there will be none left in 30 years. Furthermore, modern mining alone places a strain on the environment and a large portion of phosphorus contains high levels of heavy metals and radioactive substances that pollute the ground.

Slurry from sewage is controversial

The Swedish Environmental Protection Agency believes that human waste has the potential to create 90 tonnes of phosphorus per year, and so the Agency has set a target where at least 40 per cent of phosphorus from sewage will be used for fertiliser in Swedish agriculture by 2018.

At the same time, slurry from sewage is controversial. Dioxins, heavy metals, viruses, polymers, traces of medication and microplastics have led to several German states banning the use of sewage slurry on fields. Food companies in Sweden no longer purchase goods that have been fertilised using slurry from sewage.
“It is only a matter of time before an epidemic breaks out because of contaminated foodstuffs. Sewage slurry must be treated using methods such as incineration. It isn’t possible to measure the levels of bacteria, viruses and pharmaceuticals, no matter how much work is done to stop these harmful substances before they reach our water and subsequently our waste,” says Anita Pettersson, Docent within the area of resource recovery at the University of Borås.

For Anita Pettersson, phosphorus is a vital element in the broadest sense; It was here that the research track once started, and it was the research into reclaiming phosphorus from the ashes of sewage slurry waste that helped her take home the Researchers’ Grand Prix in 2016. Anita Pettersson can even amaze those outside the research world. Perhaps because when all is said and done, she talks about how people all over the world would be able to eat their fill and the environment would improve.
“Our research is more important than ever. Designer ash is one way to effectively recycle phosphorus and therefore we can become more economical with resources and food supply, as well as reduce algal bloom caused by phosphorus leaks,” she explains.

Collaboration with industry

In 2015, Borås Energi och Miljö began a four-year sponsorship of doctoral student Andreas Nordin and the Ryaverket combined heat and power plant has supplied Andreas Nordin and Anita Pettersson with the lab samples. The investment goes a lot further than just financing.
“One of our tasks as a public environment company is to minimise waste. This means making behavioural changes, but also stopping the cycle in a safe way. Therefore, it is beneficial to us that the University of Borås is just around the corner. The University has enormous expertise in resource recovery and social structures that contributes to upgrading our leftovers. We also receive direct dividends via the researchers’ participation in workshops, seminars, partnership discussions and monthly newsletters,” says Pär Carlsson, head of Strategic Development at Borås Energi och Miljö.
“The broad scope of activities at Borås Energi och Miljö provides a comprehensive view of environmental issues, which is an advantage to research. Their specialists serve as supervisors for Andreas Nordin. Understandably there is a commercial aspect – we are of course researching for industry – however the technology will be made available to all. The plan is to develop something that will benefit the whole world,” says Anita Pettersson.

Both Pär Carlsson and Anita Pettersson confirm that there is large interest for a safe product, and they mention both Federation of Swedish Farmers and the eco-profile Slätte gård as potential partners.

Collaboration with other higher education institutions

The results can be revolutionary, even though at first glance the research methods may seem conventional. To simplify, waste incinerators burn at 850° C, which purifies but does not destroy the waste. Between 2015 and 2016, Andreas Nordin and Anita Pettersson analysed the leftovers from incinerated sewage slurry – bottom ash, pulverised fuel ash, recycled sand, recycled ash, ash from cyclonic separation, ash from textile filters and smoke filtered at Ryaverket.

Questions to be asked
• What will the incineration processes look like?
• How will fuel optimisation take place with optimising phosphorus recovery in mind?
• How can the best vaporisation of heavy metals be achieved, and how can the additives contribute to improving growth access to phosphorus?
• Which temperatures and flows create the best energy, emissions and phosphorus effects? 

Samples have been taken both periodically throughout the year and intensively at certain intervals. We have studied how the mixture of slurry, biofuel and waste as well as the processes can be optimised with the incoming materials in mind, the incinerators’ performance and wear, plus the outcome of the usable phosphorus,” says Anita Pettersson. Laboratory studies have included everything from analysing the elements in microwave plasma to modelling programs.
“Thanks to large investments together with other research groups here at the University of Borås and at Chalmers, we have the unique opportunity to investigate structures, compounds, leaching and more,” says Anita Pettersson.

A project that has only just started

Full-scale trials using the designer ash will be carried out during 2017 by E. ON in Mora, on behalf of Borås Energi och Miljö.
“We’re still at the start of the project, and this is a real push forward. I’m very happy to have a doctoral student with both a Master’s in resource recovery and a solid background in chemistry. Together we will experiment our way to the best type of ash from biofuels and slurry until 2019, one that can be beneficial out in the fields. But we’ll never finish – there’s always room for improvement,” says Anita Pettersson.

In addition to Borås, Swedish research into phosphorus recovery is being carried out at Chalmers, Umeå University and the Luleå University of Technology.
“Unfortunately acquiring funding is difficult. We need more visionaries like Borås Energi och Miljö,” Anita Pettersson concludes.

Phosphorus
• P in the periodic table
• A finite resource
• Essential plant nutrition, included in mineral fertilisers.
• Currently, phosphorus is extracted from mines in China, USA and Morocco. However, its quality and purity varies considerably. Moroccan phosphorus is the purest.

Winner of the Researchers’ Grand Prix

The Researchers’ Grand Prix 2016 placed all eyes on phosphorus research. Facing tough competition, Anita Pettersson’s passionate four-minute speech brought home the victory, meaning that the University of Borås won for the second year running.
“What an amazing experience! At first I was sceptical, but after Almedalen Week, I gave it my all. I really hope this will mean that more people take note of the benefits of designer ash,” Anita Pettersson concludes.

Read more about Anita Pettersson.

Read more about the Combustion and Thermal Processes research group.

Read more about research at the Swedish Centre for Resource Recovery.

Text: Jessica Cederberg
Photo: Anna Sigge
Translation: Semantix