Stora Enso Barcelona SA is a company dedicated to the manufacture of cardboard for several applications in the packaging sector. During the process of manufacturing cardboard from recycling, significant quantities of wastewater with a high content of solids (sands, fibers, mineral charges) and organic material are generated. These waters are treated in a treatment plant that has a primary treatment (physicochemical) and a secondary treatment (2 biological reactors). From these treatments, purified water and sludge are generated (13,000 t/ year).

Thanks to the composition of the sludge, with large amounts of carbonates and kaolins, these can be managed as by-products in the Catalan regulatory framework by different industrial sectors, since they can substitute some of the raw materials used in other production processes. These by-products can be used in some of the manufacturing processes pointed below:

• Manufacture of ceramic material for construction, as a substitute for a part of the clay.
• Cement manufacturing, as a substitute for a part of natural calcareous stone.
• Manufacture of cellulose, as a substitute for part of the virgin cellulose fiber.

This substitution represents a saving in the consumption of natural resources and a reduction in the disposal of waste in the landfill.