F-Cubed at Venice 2022, the 9th International Symposium on Energy from Biomass & Waste
F-CUBED researcher Lucia Recchia of CA.RE FOR. Engineering presented preliminary results from the project’s environmental life cycle assessment of the hydrothermal treatment and dewatering of paper sludge. The F-CUBED process was compared to the reference case of the sludge streams processed at the Smurfit Kappa paper mill in Piteå, Sweden.
In the conventional process, streams from the paper-making process are fed to a wastewater treatment facility where nutrients, such as urea and phosphoric acid, are added. A biological sludge stream and a clean water stream are produced, the latter being discharged to the environment. Fibre sludge, produced by the paper mill, and the biological sludge are then combined to form a mixed paper sludge, which undergoes conventional mechanical dewatering using a gravity bed and screw press with the addition of polyelectrolyte and ferrous sulphate. Wastewater from this process is sent back to the treatment plant and the solids produced are used for both internal and external energy production.
The F-CUBED process has numerous advantages over the conventional method. The TORWASH® reactor decreases the moisture content of the sludge meaning that less fibre sludge is needed and, therefore, a greater amount can be recycled back into the paper-making process. It increases the amount of nitrogen in the effluent, promoting anaerobic digestion, and it produces pressed cake with reduced biological degradation and an effluent with a low content of heavy metals. The addition of anaerobic digestion to the process allows for the production of biogas and the extraction of nutrients from the digestate which can be recycled back into the paper-making process or utilised for fertiliser applications.
Overall, the F-CUBED process demonstrated a 98% volume reduction in the waste stream of biological paper sludge from the paper mill, without the use of chemicals or dewatering aids. The removal of nutrients from the digestate significantly reduces freshwater and marine eutrophication and ecotoxicity, and metal depletion, fossil depletion and overall climate impact was reduced.
The addition of the F-CUBED technologies and process steps to the treatment of biological paper sludge meant that it caused greater terrestrial acidification and ecotoxicity, agriculture and urban land-occupation and human toxicity. However, it is predicted that upscaling the F-CUBED process can mitigate these impacts relative to the amount of biological paper sludge that can be processed and the climate impact reduction in other areas.
The analysis of the results of the life cycle and environmental assessments are in their early stages and modification to the inventory data and modelisation are still possible. Nevertheless, the obtained results are promising and there are reasons to be optimistic that the F-CUBED process can help significantly reduce the waste and environmental impact of industries that produce large amounts of biogenic waste.
Subtitle: F-CUBED environmental assessment presented at the Venice Symposium
Meta-description: F-CUBED presents their findings on the impact on climate change from the treatment of biological paper sludge waste streams from the paper making industry.