From domestic sewage waste to your gas tank: advanced biofuels from sewage
In 2021, fossil fuel-powered cars and vans accounted for 92 % of light-duty vehicle sales globally. Despite the accelerating adoption of electric and hybrid vehicles, these vehicles and many more will be on the road for at least a couple of decades, so a sustainable interim solution for greener transport is needed. Carbon-rich biowaste such as sewage sludge is an excellent source of energy and energy carriers. It is renewably and locally produced with no geopolitical boundaries. Today, most of it is landfilled, incinerated or used in agriculture. The EU wants to convert it into energy. The EU funded TO-SYN-FUEL project is making this possible. TO-SYN-FUEL and its 13-member consortium demonstrated for the first time at a precommercial scale the conversion of sewage sludge into drop-in biofuels at a decentralised location. Abundant toilet waste may soon be powering our cars rather than accumulating in landfills.
From sewage sludge to drop-in gasoline and diesel
First-generation biofuels are derived directly from starchy crops like corn, cereals and rapeseed. Advanced or second-generation biofuels enhance sustainability with feedstocks like residual and waste products from households and industry that are not in direct competition with food production. “In the TO-SYN-FUEL project, crude oil was obtained via thermo-catalytic reforming (TCR®) technology from sewage sludge produced by wastewater treatment plants. The crude oil was converted via hydrogenation and distillation processes into drop-in biofuels that meet European standards for gasoline and diesel (EN 228 and EN 590, respectively),” explains project coordinator Robert Daschner of the Renewable Energy Department at Fraunhofer. TO-SYN-FUEL’s gasoline and diesel have all the properties of fossil fuel-derived counterparts and can be used directly in unmodified vehicles.
Sewage-derived biofuels go for a test drive
From 2017 to 2022, TO-SYN-FUEL converted more than 0.5 million kg of sewage sludge into approximately 50 000 l of oil, from which 40 000 l of gasoline, diesel and kerosene can be obtained. EU funding of the TO-SYN-FUEL supported the team in increasing efficiency through energetic and thermal process coupling and integrative products use and subsequent technology scaling. While sewage waste was the focus of TO-SYN-FUEL, as its disposal is particularly problematic, the TO-SYN-FUEL process can convert almost any biomass, including the organic fraction of municipal waste, agricultural residues and garden waste, into gasoline and diesel. TO-SYN-FUEL’s biofuel was on display throughout Europe. The team took an unmodified Volkswagen Passat for a road trip fuelled with biodiesel from the project’s plant. “TO-SYN-FUEL demonstrated for the first time on an industrial scale that biogenic residual and waste materials can be converted into thermally stable liquid bio-oils. Our high-quality drop-in biofuels will enable the substitution of fossil carbons with a wide range of petrochemical products obtained from biogenic residues via conventional refinery processes,” states Daschner. The team is now working on demonstrating its technology for other biomass feedstocks.
Sewage sludge prepares to take flight
A Bavarian refinery is planning the first industrial application of the technology. Sustainable aviation fuel will be derived from processing up to 400 000 metric tonnes of sewage sludge (100 000 metric tonnes of dry matter) by 2030, around 40 % of Bavaria’s total sewage volume. ‘Renewable’ sewage could soon be powering vehicles on land, air and sea.
Keywords
TO-SYN-FUEL, fuel, sewage, biofuels, biomass, crude oil, refinery, transport, thermo-catalytic reforming, wastewater treatment
