Sludge2Fuel – The first full-scale demonstration for producing biofuel from sewage sludge
Aarhus University
It sounds almost too good to be true: we can convert sewage sludge, a hazardous waste product from wastewater, into a green and renewable biofuel that can replace fossil fuels in planes, ships, and trucks.
Challenge
Sewage sludge is a problematic waste stream from wastewater treatment. Although it contains valuable materials like nutrients, minerals and carbons, it is considered as a hazardous waste because it contains a wide range of pollutants such as heavy metals, organic contaminants such as pharmaceutical residues and PFAS. Denmark is one of the last European countries where it is still a common waste management practice to spread sewage sludge on agricultural fields. This is not only an environmental issue, but also a loss of valuable nutrients and energy-rich carbon.
Solution
The Sludge2Fuel project will validate the world’s first full-scale implementation of conversion of sewage sludge into sustainable biofuel and fertilizer. This will be achieved using hydrothermal liquefaction (HTL), a disruptive technology out of the labs of Aarhus University, that may change the way we look at revolting waste streams such as sewage sludge. Much like the geological formation of fossil oil, in HTL, biomass is heated to high temperatures of 200-350°C at high pressure of 150-350 bar converting the organic carbon into biocrude.
If upgraded, the oil can be distilled into drop-in fuels that replace fossil fuels. Phosphorus, an essential nutrient for food production, can be fully recovered, extracted and turned into a clean fertilizer. Furthermore, environmentally hazardous heavy metals are concentrated in a minor solid fraction, and microplastics and organic micropollutants such as drugs residues are destroyed. Our recent research shows that even PFASs can be degraded. One of the last challenges that we need to deal with, is the treatment of a process water produced by HTL, containing high concentrations of organic compounds. As part of the Sludge2Fuel project, we showed the treatability of this process water in conventional activated sludge and assessed the biodegradability and environmental impact of a wide range of HTL-derived organic pollutants to ensure no negative impact of the effluent on the environment.
Implementation
In the Sludge2Fuel project funded by EUDP Denmark, Leendert Vergeynst, Patrick Biller and Kostantinos Anastasakis from Aarhus University collaborate with the company Circlia Nordic producing HTL reactors to demonstrate the first full-scale implementation of HTL. Krüger A/S supports the technical implementation, and Crossbridge Energy refines the biocrude to drop-in fuels.
The new demonstration plant is the size of two 40-foot containers producing 1400 tonnes of biocrude oil per year and will be implemented at the wastewater treatment plant of Fredericia (Fredericia Spildevand og Energi). In theory, all the sludge from all Danish wastewater treatment facilities would correspond to approximately two per cent of the nation’s total consumption of fossil fuels. HTL can’t produce oil for running all the cars in Denmark, but it could produce substantial volumes of biofuel for heavy transport such as aviation, trucks, and ships, which are difficult to electrify. Sludge2Fuel expects to produce the first biofuels from sewage sludge by end 2024.
Results
Researchers at Aarhus University have spent thousands of hours on developing the technology, and together with daring industrial partners, this will culminate soon into the first full-scale production of biofuel from the sewage sludge at the wastewater treatment plant of Fredericia.
In the future, HTL may be relevant not only for management of sewage sludge, but also for management and recovery of resources of other hazardous waste streams such as manure, slaughterhouse waste and other industrial wastes. If we can fulfil HTL’s promises, there is a great potential for growth and export to many other countries where management of sewage sludge poses challenges.
Partners
Aarhus University, Crossbridge Energy A/S, Circlia Nordic ApS, Krûger Veolia, and Frederecia Spildevand og Energi A/S.
Contact
Leendert Vergeynst
Associate professor, Aarhus University
leendert.vergeynst@bce.au.dk
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