Munich Robert Daschner lifts a bottle in which a black liquid is sloshing. “The appearance and chemical properties are comparable to crude oil,” says the 37-year-old mechanical engineer proudly. Daschner and his employees at the Fraunhofer Institute “Umsicht” extracted the oil from sewage sludge, which the municipalities would otherwise have burned at great expense.
Daschner points to the system behind him. In this “snail reactor” in Hohenburg, Bavaria, the researchers first heat the sewage sludge to more than 450 degrees. During pyrolysis, steam and char are produced. The scientists then direct the steam over the “coal bed”. During cooling, process water and oil are produced, which the researchers separate. In the end, what remains is a stable “bio-crude oil”.
Just a few years ago it would have been unthinkable to produce such a high-quality substitute for crude oil in large quantities from residues such as sewage sludge, says Daschner. But his plant can convert up to twelve tons of sewage sludge into 1,200 liters of biogenic crude oil per day. That in turn is enough for 950 liters of fuel: kerosene, gasoline – and about 370 liters of diesel. Depending on consumption, a car can cover more than 6100 kilometers.
Climate-neutral gas from leftovers
1.9 million tons of sewage sludge are available throughout Germany, a potential raw material for around 200 million liters of oil. And the process can be used to process many other organic residues and waste materials. For example for raw materials in the chemical industry. Or as a drive for airplanes or ships. “For everything that is currently difficult to electrify,” says Daschner. The advantage: The biogenic fuels are climate-neutral, so unlike fossil fuels they do not emit any additional CO2.
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Nevertheless, unlike in many European countries, diesel made from biogenic residues and waste is not permitted in its pure form in Germany and may only cut fossil fuels by up to 26 percent. Probably also because energy sources from biomass have had a difficult time in Germany since the “tank-plate debate”. The concern that persists to this day: The area under cultivation could displace that of food. Advanced biofuels are now based on residues.
Christoph Spurk, Vice President of the Biogas Association, says: “Although our biogas plants today ferment a large proportion of waste and residues in addition to renewable raw materials, bioenergy is still reduced to corn. That no longer corresponds to the state of the art”. Karin Naumann from the German Biomass Research Center (DBFZ) also complains that “in few countries bioenergy is viewed as critically as in Germany”. So far, the moment has been missed to conduct the discussion about competition for use objectively.
Biogas, which is produced by fermenting manure, for example, can be converted into electricity, heat and biomethane, a renewable alternative to natural gas. According to the Biogas Association, around 9,000 systems in Germany ensure a feed-in of 3,800 megawatts (MW). That’s just a little less than the last three German nuclear power plants produce and covers around five percent of Germany’s electricity consumption. According to Christoph Spurk, the systems could produce 1000 MW of additional electricity throughout the year. But that complicates the bureaucracy. The federal government recently lifted a capacity cap for biogas plants. But not for all standards, as implementation questions remained unanswered.
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Germany is one of the largest bio-energy producers and is considered a technology leader. Still. “In the meantime, we’re going to France with our biogas customers to show the state of the art in the large plants that are in great demand there,” says Spurk. He looks at his neighbors with envy. Every year, 200 new biomethane plants are built there, and by 2030 it is expected to be 2,000. In Germany there are a total of 250. Or Denmark: By 2034, the country wants to cover all of its gas requirements with biomethane, mainly from domestic residues.
Spurk fears that as long as Germany slows down the industry, it will continue to generate 90 percent of its sales abroad. He is hopeful that the EU Commission intends to double its biomethane production to 35 billion cubic meters per year by 2030.
The position of the Ministry of Economics and Climate Protection (BMWK) is different: It finds a “substantial increase” in biomethane production to replace natural gas “hardly possible in the medium and long term and also not necessarily sensible”. Because the amounts of biomass that do not have to be cultivated separately are limited.
78 terawatt hours are unused
On the one hand, that’s true. But why do without unused leftovers that could immediately reduce emissions? Fraunhofer researcher Daschner speaks of the “Eh-Da-Potential”. The Bayernoil refinery also wants to produce oil from sewage sludge in the future. And Daschner receives inquiries from all over the world, for example from Canada. There, vast amounts of unusable wood rotted in Canadian landfills and emitted methane.
In Germany, too, there is still a lot of “Eh-Da-Potential”. According to FV-Biogas, 400 biowaste fermentation plants currently generate 350 megawatts, mainly in electricity generation. That could be doubled if one were to use four and a half million tons of organic waste that ends up in the residual waste or is heavily contaminated. That could cover the electricity needs of 360,000 four-person households, Spurk explains.
And the DBFZ also sees large amounts of “mobilisable biomethane potential” from waste and residues. According to this, up to 78 terawatt hours (TWh) are idle, which corresponds to about a third of German heavy goods traffic. The total energy consumption in road traffic in Germany in 2020 was 565 TWh. But how these substances are used is a political question, says Naumann. The environmental engineer hopes that the biomass strategy envisaged for 2023 will lead to an “appropriate discussion on the development and use of this potential”.
Not only can fuel or biogas be produced from biomass, but also CO2 for the production of hydrocarbons such as methanol or ammonia. In the future, these are to replace crude oil-based fuels, for example in heavy goods traffic. “If the CO2 for production is not to be fossil, it will initially be biogenic,” says Naumann. Filtering CO2 out of the air is considerably more expensive and complex. So far, however, politicians have hardly kept an eye on this synergy.
Kerosene from deep fry fat
In addition to such synthesis processes, there is an important area of application: extracting and storing CO2 from the atmosphere. Daschner grabs a glass with small black chunks. “With our pyrolysis, part of the carbon remains firmly bound in the carbonate.” The carbonate could be spread over the fields as fertilizer, as long as it doesn’t contain any heavy metals – but that is the case with coal from sewage sludge. According to the UN Climate Change Council, huge amounts of CO2 must be removed from the atmosphere. If the carbonate is not burned, the CO2 remains bound in it.
But there are other criticisms of bioenergy. According to Carla Vollmer from the Federal Environment Agency (UBA), the energy required for generation, production and transport is often disproportionate to the yield. For example when using low-energy liquid manure or algae. In addition, leftovers can often still be used as material. For example, wood chips as building material for chipboard to bind the CO2 in the wood in the long term.
Vollmer also sees the risk of misguided incentives: that “not just leftovers” end up in plants, that energy crops displace food and land in distant countries. That biogenic fuels inhibit investments in “more promising” fuels produced with renewable electricity such as “Power to Liquid” (PtL) kerosene.
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Objections that Mercedes Alonso from Finnish company Neste, the leading manufacturer of renewable jet fuel and diesel, cannot understand. Neste researches “low-quality raw materials” and mainly uses waste and leftovers such as used oils and fats from the catering trade for its production. Airports such as Munich, Frankfurt or Cologne already offer Nestes aviation fuel. In addition, the renewable raw materials for the plastics and chemical industries are found in coffee capsules or cups, for example.
“We will not be able to refuel all aircraft worldwide with the available quantities.” But just waiting for electric or hydrogen drives, where emissions can already be reduced with bio-based fuels, is a “missed opportunity”, according to Alonso. In its pure form, the “sustainable” aviation fuel reduces greenhouse gas emissions by up to 80 percent over its life cycle compared to fossil kerosene.
Robert Daschner also doubts that investments in biogenic fuels stand in the way of other technologies. “We can’t afford either/or. We now need interim solutions that replace fossil products. We need everything, and fast.”
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