RemErgy - Biogas production from fiberbanks: combining sediment remediation and energy production

The overall aim of this 4-year FORMAS project is to limit both contaminant dispersal and uncontrolled greenhouse gas (GHG) release from contaminated fibrous sediments to the atmosphere. To achieve this aim, the project will combine the remediation of fiberbanks with its valorisation to biogas. The work is structured in 4 work packages (WP), each addressing a specific objective:

1. Reaching an efficient biogas production from different types of fiberbank sediments (WP1)
2. Quantifying degradation and emission of contaminants during the biogas production (WP2)
3. Characterizing the organic matter (OM) in the various fiberbank types and understanding how it is impacted by anaerobic digestion and biogas production (WP3)
4. Identifying the microbial communities responsible for gas production and possible other chemical transformations, to understand the changes following biogas production (WP4).
    

Environmental pollution from the pulp and paper industry

The paper and pulp industry used to be one of the most polluting industries. The factories used to reject both contaminants and large amounts of wood products to the aquatic environment until a new regulation came into force in 1969. The fibrous material that was rejected before has sedimented and built up large banks on the seafloor, so-called “fiberbanks”. Fiberbanks are highly contaminated with organic pollutants and metals, and they have been found in large volumes in the few places that have been surveyed so far. It is suspected that fiberbanks can be found in more than 380 sites in Sweden. They have also been identified in other countries.

Converting waste to energy

The organic material in the fiberbanks degrades continuously (through microbial anaerobic digestion), generating large amounts of gas released, which limits in-situ capping remediation solutions. Dredging followed by on-land treatment can therefore be a more efficient remediation action for fiberbanks. The gas produced within the fiberbanks is composed of methane and carbon dioxide, which are greenhouse gases contributing to climate change. However, methane can be used for producing energy such as electricity, fuel and heat, via biogas production. Therefore, this project aims to investigate whereas fiberbanks can be a sustainable source of biogas after dredging.

Optimisation of the degradation process

In RemErgy we are testing three different typical types of fiberbank material, sampled from three sites in the Ångermanälven river estuary. We investigate in the laboratory how the anaerobic digestion can be optimised in order to produce as much gas as possible. This can depend on the additives used but also on various parameters such as temperature, bacterial community, and fibre type. The anaerobic digestion can also influence the sediment in different ways, which can have more positive effects than the only production of energy. While the fibrous material is consumed, its volume should decrease, which would lower the amount of material needing to place in landfills. Anaerobic digestion can enhance contaminant degradation into less toxic products, thus reducing the contamination levels in the treated sediment. Finally, this solution will limit the non-controlled greenhouse gas emissions from the seafloor. All these effects will be studied in the laboratory, aiming to improve the effectivity of the process.

Dredging - remediation - energy recovery

RemErgy aims for a better use of our resources through combining remediation dredging and energy production, which should have positive effects on both the economy and the environment. Considering the negative impact that fiberbanks have on the aquatic and atmospheric environment, through the dispersion of contaminants and greenhouse gases, it is important to find sustainable remediation methods for fiberbanks. The production of energy through biogas is a bonus that can help balancing the costs for dredging and monitoring post-dredging, which could lead to a higher number of sites being remediated. This would help Sweden reach the environment quality objective “a non-toxic environment”, but it will also contribute to “a balanced marine environment, flourishing coastal areas and archipelagos” and “a reduced climate impact”.