Sludge Solution
Honext is a building material made from paper sludge (image: Choreo).
Back in 2011, a paper mill approached the Universitat Politècnica de Catalunya with a problem. “A huge problem,” explains Pol Merino. “The primary sludge.”
Primary sludge is exactly what it sounds like. As paper is recycled, the cellulose fibres within the material become shorter. “It’s a really stressful mechanical process for the fibre, which is damaged quite badly,” says Merino. “So after a point, the [shortened] fibre simply falls through the filter and cannot be recycled any further.” This is the primary sludge, a cellulosic slurry to which Honext estimates 10 to 15 per cent of recycled cellulose is lost, causing around 7m tonnes of it to be produced each year. “There are two options,” says Merino. “Incineration or landfill.” Poor sludge.
A problem, then, but one to which a solution began to emerge. “If you take paper, put water on it and shape it, then it has some strength once it has dried,” Merino explains. “That’s because cellulose fibres have a natural ability to form hydrogen bonds. When we saw the waste, it was really the worst fibre you could imagine, but it still had those same properties.” The university’s team knew that the primary sludge could never become paper again, but they still wanted to see whether it could be moulded into something new instead.
The result is Honext, a material predominantly used as a construction board in the style of MDF or drywall, which can be used as either interior partitioning or as interior cladding. Honext has similar functional traits to these competitor materials but differs in that it does not include binding resins, which are non-recyclable and can, in the case of MDF, emit harmful particles such as formaldehyde. By contrast, Honext is entirely recyclable, made using only the primary sludge in conjunction with non-toxic additives to aid with moisture resistance and to ensure fire retardancy. “We love our material, but ultimately it’s a partition in a building,” says Merino, who serves as the company’s managing director. “Honext has to have the lowest environmental impact possible, because otherwise, the building is going to look really nice, but we’ll have destroyed the world to build it.”
The trick, of course, is moving from that primary sludge to the final board. “That’s the work of an enzymatic cocktail,” Merino explains. Enzymes increase the surface area of the damaged cellulose fibres, allowing the matter to be shaped in a press. With the application of heat, the material can then dry into its final form. It is a complicated process, but one which the company is hoping to roll out more widely. Honext’s first plant is based at the Vacarisses Waste Treatment Facility in Catalonia, but the company is now finalising a modular version of their equipment that can be installed directly within paper mills.
“Instead of trying to build a huge site and have the raw materials shipped in, we can go inside paper mills and locally transform waste that would otherwise go into landfill,” says Merino. “We envisage a distributed production network and we want the mills to operate this. They won’t have the costs of incineration or landfill any more, and we’ll pay them to operate the site.” If the plan comes to fruition, it’ll be a lifeline for sludge everywhere.
Words Oli Stratford
Photographs Choreo
This article was originally published in Disegno #29. To buy the issue, or subscribe to the journal, please visit the online shop.