Share article
Pulp and paper mill sludge
Material description and quantity estimation
Pulp and paper mill sludge is sludge that is produced during the treatment of wastewater derived from a paper mill. The pulp and paper mill sludge from different paper mills varies in consistency. Pulp and paper mill sludge that mainly consists of potassium carbonate and cellulose fibre is produced at Stora Enso Oyj’s Oulu mill during the mechanical pre-sedimentation, which is a wastewater treatment process. Of pulp and paper mill sludge, approximately 85% consists of potassium carbonate and 15% of cellulose fibre. The dry matter content of the sludge is 30%. (Pöyry 2007.) 
At Stora Enso’s Oulu mill, approximately 25,000 tonnes of pulp and paper mill sludge is produced annually. The corresponding amount for the rest of Finland is difficult to determine, as the consistency varies. There are, however, no paper mills operating in the regions of the rest of the six largest cities in Finland, so the pulp and paper mill sludge was deemed a relevant material flow only for the Oulu region. Kiertokaari has previously utilised pulp and paper mill sludge in earth construction by applying it to the compaction layer of a landfill site’s base structure instead of virginal raw materials. Due to the Government Decree on Landfills (VNA 331/2013), which bans the dumping of organic waste at landfill sites, it has been forbidden to dump sludge at landfill sites since the decree entered into force at the beginning of 2016, and there is no need to construct new landfill areas in Oulu. Due to the soluble nickel and fluorine contained by the material, pulp and paper mill sludge cannot be utilised in other types of construction applications (e.g., in side banks and noise barriers) to a significant degree (Pöyry 2007; VNA 403/2009).
Innovation needs
The large amount of pulp and paper mill sludge, the landfill ban on organic waste, and the loss of the previously used recovery method create a need for new innovations.
- Need for developing new applications and treatment methods
- Limited storage space at the waste treatment areas increases the pressure to develop a quick and effective sludge treatment method
Need for reducing the amount of soluble substances contained by sludge under the limit values, as these substances currently restrict the utilisation of pulp and paper mill sludge in earth construction
Business-related challenges and opportunities
Even though the volume of paper production has decreased in Finland over the past ten years, still 10.3 million tonnes of paper was produced in 2017 (Metsäteollisuus ry 2018). In quantitative terms, large amounts of pulp and paper mill sludge will be produced in Finland in the future, as well. If solutions to the innovation needs arisen during the review are found in the future, the costs incurred by treatment can be reduced while improving the business potential of pulp and paper mill sludge.
References (mainly in Finnish)
Valtioneuvoston asetus kaatopaikoista, 331/2013.
Valtioneuvoston asetus eräiden jätteiden hyödyntämisestä maarakentamisessa annetun valtioneuvoston asetuksen liitteiden muuttamisesta, 403/2009.
Pöyry, 2007. LAANILAN VOIMA OY, STORA ENSO OYJ JA OULUN ENERGIA – VOIMALAITOSTUHKIEN LOPPUSIJOITTAMINEN, YVA-SELOSTUS
Metsäteollisuus ry 2018: PAPERIN JA KARTONGIN TUOTANTO SUOMESSA.