A EU-funded project aims to unlock the biogas potential for the pulp- and paper industry while improving its overall energy efficiency. In Sweden alone, the industry has the potential to produce up to 1 TWh of biogas by retooling its wastewater treatment.
Recently, Sweden-based biogas technology developers Scandinavian Biogas revealed it had received EUR 3.1 million in EU funding to build a demonstration plant at a pulp mill. The ‘EffiSludge for LIFE – An innovative concept to improve resource and energy efficiency in treatment of pulp and paper industry effluents’ project is partially funded by the LIFE programme, a funding instrument for the environment and climate action to contribute to the implementation, updating and development of EU environmental and climate policy and legislation.
The core objective of EffiSludge is to build and operate the first dedicated pulp- and paper mill wastewater biogas demonstration plant that will clean as good as or better than conventional pulp mill wastewater treatment processes yet produce more biogas, leave less post-treatment residual sludge while using less energy to do so. By modifying an existing aerobic treatment step and integrating it with an added anaerobic digestion (AD) stage the aim is to demonstrate at scale the technical and economic feasibility of such a treatment plant.
More sludge
Typically wastewater treatment at a pulp mill consists of a primary treatment step such as flotation, sedimentation and filtration to remove suspended solids such as fibre and bark. This is followed by an aerobic treatment stage to remove dissolved organic matter using microorganisms thus reducing the chemical oxygen demand (COD) in the water.
Normally this step is operated to obtain the lowest possible sludge yield, while achieving a high COD-reduction as the residual sludge from this process is seen as a waste to be disposed of and not as a resource. In essence the idea of EffiSludge is to optimize the aerobic stage for sludge production and use the sludge as the substrate for the added AD stage to produce biogas. The final volume of residual sludge will also be less.
Up to 1 TWh potential
The EffiSludge project stems from a recently concluded Swedish Energy Agency funded research project ‘Establishment/optimization of biogas production in the pulp and paper industry’ conducted during 2011-2015 by a consortium with Linköping University, Scandinavian Biogas and Pöyry. The project demonstrated that the Swedish pulp- and paper industry could generate up to 1 TWh biogas per annum by taking a different approach to processing sludge produced as part of mill wastewater treatment while simultaneously reduce energy consumption.
A number of different concepts and investment costs are presented as costs, biogas yields and energy savings in wastewater treatment vary depending on the reactor and mill type, sulfite, sulfate or mechanical pulp. The report suggests that for an average sized Swedish mechanical pulp mill, an SEK 64 million (≈ EUR 6.73 million) investment could yield in the order of 18 GWh of biogas and reduce wastewater treatment energy consumption by 50 percent per annum.
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