2017-05-24 11:38

New method for classifying ash important to energy companies

The ash from burning waste is classified either as non-hazardous or hazardous waste. Now researchers from the University of Borås together with three other labs will make parallel attempts to develop a new method for classifying bottom ash – an issue important to energy companies in Sweden.

Leach testsPreviously, this type of methods for classifying bottom ash has not been regarded necessary. Instead, it has been assumed that the material is stable – non-hazardous – since the material is tightly bound in the ash and does not dissolve. But the proposal now with the EU would mean that all bottom ash would be classified as hazardous waste.

– If you used this method on natural stone, it would become hazardous waste since you dissolve the entire stone and don’t care if that which is in the stone is tightly bound and stays there or not. That’s why it’s not dangerous, explains Anita Pettersson, Associate Professor in Resource Recovery at the University of Borås.

Leach tests are part of the new methods. This means that the researchers put ash in water, in this case, but there can also be other solutions, and stir.

– At the moment, we’re testing 50 mg of ash in 5 litres of water and then we test it after 2, 4, 7, 14, and 28 days to see what has dissolved into the water. It’s primary copper and lead we investigate but other metals too.

If the ash is considered hazardous waste depends on whether the metals dissolve or not and in what amount.

Anita Pettersson– For example, if you see that almost no copper dissolves, and after a week it has stabilised and nothing more dissolves, that’s fine. Bu then all elements must be weighed into the final assessment. That's quite complicated, and different elements are weighed differently depending on how dangerous they are considered to be in the environment, she says.

All four labs make the same leach tests but with different ashes. The ashes come from different boilers from different companies that incinerate waste.

– Even though all boilers are waste boilers, the ashes turn out differently depending on the boilers being different and all waste comes from different companies and cities etc. We try to make these tests in parallel because they take a lot of time. We have contact at least once a week to exchange experiences and work as similarly as possible. 

– We hope to present a new test method for bottom ash before the end of this year, Anita Pettersson says.

The other labs participating in the project are Vattenfall, the Swedish Geotechnical Institute, and Renova. Anette Hälldal at Vattenfall is the leader of the project.

The project is funded by the Swedish Waste Management Association, Vattenfall, the Swedish Geotechnical Institute, Eurofins, Renova, Sysav, E.ON, Fortum, and Tekniska verken. 

Text: Anna Kjellsson
Photo: Anna Sigge
Translation: Linda Lindstedt