The pulp and paper industry in Europe and globally is a major user of electricity and emits large quantities of CO2 (five per cent of the world’s total industrial energy consumption in 2007, amounting to two per cent of direct CO2 emissions from the industrial sector). The wastewater treatment within pulp and paper industry normally comprises a primary treatment for removal of suspended solids such as fibres and bark particles. Sedimentation, flotation and filtration techniques can be applied. The remaining wastewater needs to be cleaned to remove dissolved organic matter and an aerobic biological treatment is thus applied (high amount of energy and nutrient needed). Chemical oxygen demand (COD) is reduced by the action of active microorganisms, degrading the organic matter in the wastewater. Normally the biological treatment is run to obtain the lowest possible sludge yield, while obtaining a high COD-reduction. One of the reasons is that the sludge is seen as a waste that needs to be disposed of and not as a resource. The waste sludge within pulp and paper production is often dewatered and disposed of by incineration.
The main aim of the EffiSludge for LIFE project was to build and operate the first ever demonstration plant that substantially increases the biogas potential from wastewater generated within the pulp and paper industry, and at the same time lowers electricity consumption by 50% and replacing 90% external commercial chemicals with nutrients from fish waste. The project would introduce an innovative process at industrial scale, by modifying the aerobic bio-treatment for biomethane production from the organic matter in the wastewater first and the increased production of waste sludge. The waste sludge from the bio-treatment would be used as a co-substrate for anaerobic digestion to biomethane of fish waste, with sludge production being optimised for this purpose. The final volume of residue sludge, after implementation of the EffiSludge concept, including anaerobic digestion, would be less than if the actions had not been implemented. Furthermore, residual nutrients from the anaerobic digestion of fish waste would be recovered.
As a result of the EffiSludge for LIFE project, the existing industrial wastewater treatment plant at the Norske Skog Skogn paper mill, north of Trondheim in Norway, was equipped with an integrated and newly-built biogas plant.
The new wastewater treatment cleans process water from the paper mill, while biogas is generated from both the wastewater itself, and using residues from the wastewater treatment process in co-digestion with waste from the Norwegian fish industry.
This symbiosis resulted in multiple benefits:
- Production of renewable fuel (over 13 700 MWh/year as biogas equivalent from the wastewater and the biosludge);
- Energy savings (12% reduction in electricity consumption achieved during the project);
- Recirculation of nitrogen and phosphorus by replacing 90% of urea and phosphoric acids used in the wastewater treatment plant with a liquid fraction of the digestate from the biogas plant;
- Reduction of 96% of the carbon footprint due to substitution and recycling of nutrients, energy savings and production of biogas (decrease from 0.464 kg to 0.018 kg CO2 emission per m3 wastewater achieved).
Further information on the project can be found in the project's layman report (see "Read more" section).