Forest waste turns sewage into tiles

Wood Focus magazine
30 Dec 2011
(chair in a forest)

Forest waste is being used by researchers from the Polytechnic University of Catalonia, based in Barcelona, Spain, to manufacture structural ceramics using sewage sludge.

The method involves adding forest waste, such as sawdust from shredded furniture, into a binary mixture of illitical clay, which enables the sewage to be assimilated into an extrudable mix. The use of forest waste enhances the ceramics properties, says Professor Martin Devant. ‘The key is that with the addition of forest waste you can add more sludge.’

The research looks to capitalise on the large quantities of sewage sludge being generated – which is approximately 400g per person every day, according to Devant.

Researchers found the ideal composition to be 10% sludge, 10% forest waste and 80% clay, which yielded a compression strength of 96kp/cm2. ‘This is the bulk compression to finally obtain a perforated brick with 50kp/cm2, which is an acceptable minimum,’ he says.

The mixture would be suitable for producing ceramics with low thermal conductivity and high porosity, which would be the same as a ceramic brick, because all the organic compounds are thermally destroyed, but with a high porosity, says Devant. He adds that the bricks would be perfectly suitable for applications such as thermal isolation walls.

In terms of environmental criteria, Devant says the process is only as energy intensive as a normal brick factory. ‘The method is cost effective, because the brick factory will be paid to recycle the sludge.’ The researchers also tested the environmental aspects of production using leaching and outgassing tests.

Though research in this area has been done before, Devant claims, ‘nobody has used forest waste and sludge at the same time’.

Christopher Hall, Emeritus Professor of Materials at the University of Edinburgh, said ‘It is important to be cautious about the durability of the product. This is an example of a long-term property that is not easy to assess, and if changes are made to composition or firing temperature then there may be unanticipated consequences.’