Biobased upcycling: From residual to resource

Produce, consume, dispose - many value chains are one-way streets. One goal of the bioeconomy is to establish closed-loop systems in which as few substances as possible are discharged from the cycle. To achieve this, not only must natural raw and waste materials be processed, but ideally they must also be used several times and reprocessed or completely recycled.

In nature, biological resources enter into material cycles. The metabolism of living organisms is part of the larger carbon and nitrogen cycles. The use and regeneration of resources are in balance. No waste or residues are produced in the process.

Biomass, the central raw material of the bioeconomy, is not only a renewable resource. Compared to other forms of raw materials, it is particularly well suited for sustainable use in cycles. This includes both material use and composting. At the end of a recycling chain, biomass can also be used for energy. Bio-based cycles are possible where organic raw materials are already used. Bio-based alternatives to conventional materials and production processes can also be developed.

Resource efficiency as a sustainability strategy

A key to the biobased circular economy is the efficient use of resources along the entire value chain. Generating more from less - this applies to product design, production, consumption and the recycling of waste. The goal is to decouple economic growth and resource consumption.

The concept of cascade utilization is of central importance here. It aims to use existing biobased resources sustainably and as completely as possible - i.e. with all their components. The central objective here is the multiple use of biomass. First, the carbon bound in biobased products is used materially. The material use should take place as often as possible until, at the end of a material use phase that is as long as possible, the carbon is released again in the form of CO2 during energy use. The combined material and energy use of biogenic resources is also referred to as co-use.

Take wood as an example: cellulose is turned into paper, waste paper is further processed into paper, then into insulation material for buildings, and eventually it is burned as a material for energy production.

Biorefineries are an example of resource efficiency in industrial production processes. Here, cascade and co-utilization are implemented particularly consistently. The plant material mixture biomass is converted into a broad spectrum of intermediate and end products with the aid of various technologies and thus utilized as completely as possible.

The potential of agricultural and industrial residues comes into focus

The largely untapped potential of crop residues and residual materials such as straw, forest residues or liquid manure is increasingly coming into focus. In addition, there are residual materials that are produced during industrial production and further processing: These include classic biological waste materials such as rapeseed press cake, algae residue biomass, fermentation residues, whey or fruit peels. But waste streams such as CO2 or sewage sludge also belong to the residual materials. There are promising developments in biotechnology in the direct use of CO2 or industrially produced synthesis gas as a carbon source. For example, carbon-containing gases from steel mills or biogas plants can be used to produce biobased chemicals with the help of microorganisms. This microbial use of CO₂ makes it possible to close the carbon cycle through industrial processes and make it climate-neutral.

Biotechnology for recovery

Microorganisms and enzymes can also contribute to the recovery of rare metals or phosphorus. By breaking down plastics into their basic building blocks, they point the way to biotechnological plastics recycling. Closed nutrient and material cycles also play an important role in innovative agricultural systems such as indoor farms. Here, modern cultivation technologies are cleverly combined and organic waste and residual streams are used in a targeted manner.

For some years now, scientists have been conducting intensive research into the recovery of valuable materials from residual and waste streams, and experts have already been able to develop some processes to the point where they have made it into industrial practice. This topic dossier presents innovative approaches from research and development.

The efficient material and energy use of biogenic residues, by-products and wastes offers numerous opportunities to move closer to the UN sustainability goals and the objectives of the National Bioeconomy Strategy.

The advantages of using residual and waste materials are that many of them are not currently being used and are therefore available at favorable prices. In addition, they provide access to biomass that does not compete with food or feed. Last but not least, the use of residual and waste materials is resource-conserving and environmentally friendly. In order to be able to estimate the quantities of residual materials generated, the German Biomass Research Centre (DBFZ) has compiled a collection on the resource provision and use of biogenic residues, by-products and wastes from five sectors as part of the national bioeconomy monitoring.

Here is a representative selection

There is a technically usable supply of raw materials in the amount of 85 to 140 million tons of dry mass. More than 80% of this quantity comes from agriculture and forestry. The remaining 14 to 50 million tons can be described as mobilizable. The five biomasses of cereal straw, forest residues (needles), cattle manure, cattle slurry and green waste account for the lion's share of the mobilizable potential.

An interactive resource database is available at webapp.dbfz.de, which can be used to research biomass residue streams for different industry sectors and biomass types. The website also allows an impact analysis to show the relevance of single or multiple residues for different applications.

Straw, sawdust or fish excrement: Agriculture, forestry and fisheries produce large quantities of biogenic residual and waste materials, which are often not processed or only processed to inferior quality. Many research projects are therefore working to isolate the valuable substances contained in these residues or to use them directly as raw materials for the biobased production of higher-value compounds.

Straw is a typical by-product of the grain harvest. Germany produces an estimated 43 million tons of fresh straw, mainly cereal straw. Between 20 and 30 % of the straw produced is available for energy and material use, but is not yet utilized to the same extent. In agriculture, straw is used for soil cultivation, as bedding or as animal feed. In addition, straw finds application in the packaging and building materials industries and can potentially be used in biogas plants or for heat generation. However, straw can also serve as a feedstock for platform chemicals in the chemical and pharmaceutical industries or be processed into modern fuels.

The specialty chemicals group Clariant, for example, produces cellulosic ethanol from straw using the so-called Sunliquid process. Both in a demonstration plant in Straubing, Germany, funded by the German government among others, and in a large commercial biorefinery in Romania, the lignocellulose from the straw is broken down into sugar molecules and then fermented by yeasts to produce ethanol. Also based on straw is the pulp produced by the Swedish company Essity in Mannheim. BluCon Biotech, a company funded by the German Federal Ministry of Economics, extracts lactic acid from straw.

The BMBF-funded NPBioPhos project is investigating how phytic acid can be obtained from previously little-used residues from grain processing. This is used as a specialty chemical to refine textiles or to purify industrial wastewater from heavy metals.

The EU research network BIOMAT aims to develop nano-based foam and composite materials for the construction and automotive industries as well as for furniture, at least half of which are to be made from renewable raw materials. Among other things, the researchers are relying on nanofillers from agricultural waste materials such as rice husks, which should also improve material properties such as durability.

From the field back to the field: The ASHES project uses bagasse ash as a raw material for the production of fertilizers. Bagasse is a byproduct of ethanol production from sugar cane. The ABC4Soil project also develops fertilizers by processing biochar enriched with nutrients from manure. The biochar is produced by thermochemical decomposition (pyrolysis) of agricultural residues.

Hamburg-based start-up BIO-LUTIONS and Brandenburg-based Zelfo Technology GmbH use wheat straw, rapeseed straw, reeds or vegetable stalks as a source of fiber to produce packaging and eating utensils by means of a mechanical process. A production facility is currently being built in Schwedt, Brandenburg.

The team behind HanAkku relies on high-tech: The researchers functionalize hemp hurds, the woody pulp of the hemp stalk that accumulates after the hemp fiber is mechanically separated. The hemp hurds are specifically loaded with chemical substances and can release these absorbed substances in a controlled manner in the respective application.

In the MaiD project, corn spindles are used as a raw material for a blow-in insulation material. All these approaches offer, not least for farms, the opportunity to generate additional income with materials that are already being produced today but have so far been considered waste.

In forestry, much of the utilization of residues revolves around the main component of wood, lignin. In general, wood residues are considered chemically interesting raw materials due to their lignin content. Applications range from lignin-based carbon fibers to specialty chemicals. For example, the BMBF-funded FeruBase project is researching how ferulic acid can be obtained from wood waste. Vanillin can be produced from ferulic acid, but some antimicrobial substances for cosmetics are also based on it.

Utilize marine residues

The utilization of aquatic residual biomass is a focus of the innovation space "BaMS - Bioeconomy on Marine Sites". For example, researchers want to use the residues from mussel and algae farming - such as too-small mussels and macroalgae pomace - to produce fish feed for aquaculture facilities. Another project in the innovation space is developing integrated farming of grouper and saltwater plants in closed marine aquaculture loops and converting the residues into biochar. And another project is using nutrient-rich wastewater from fish farms to feed floating constructed wetlands.

The Cubes Circle project is about fish farming in combination with insect farming and plant cultivation. The aim is to network the various agricultural production systems in closed energy and material cycles in such a way that plants, insects and fish are co-cultivated in production units that communicate with each other and residual materials from the respective other production processes are used.

The fashion industry is also increasingly discovering sustainability. The Kümmersbruck-based company Qnature, for example, is generating interest in the industry with its Qmilk fiber. Qmilk is obtained from lactic acid from whey that cannot be marketed. Fibers made from pineapple leaves, which are not otherwise used, are now also being processed by several fashion labels. Also new to the fashion industry is a bio-based artificial leather. It is obtained from the mycelium of fungi that feed on molasses or other agricultural residues.

By-products and waste streams from food production are often not edible or at least not attractive enough to market. Nevertheless, they usually contain valuable ingredients such as proteins or fatty acids. As animal feed or chemical raw materials, these residues can therefore be used to add value and close material cycles.

Insect larvae as recyclers

What is no longer edible for humans is still tasty to insect larvae. For example, participants in the InProSol research project feed the black soldier fly with food waste in order to use its larvae as a protein source for fish feed. The fly larvae build up biomass very quickly and also have a high-quality protein composition. In the innovation area NewFoodSystems, the reKultI4Food project also follows this approach and aims to optimize processes to make them economically competitive. The Competitive Insect Products project, on the other hand, is looking not only at the protein content of insects but also at possible applications for their fats. For example, olefins could be obtained from insect larvae as biobased and biodegradable high-performance lubricants.

What is no longer edible for humans is still tasty to insect larvae. In the InProSol research project, for example, the black soldier fly is fed with food waste in order to use its larvae as a protein source for fish feed. The fly larvae build up biomass very quickly and also have a high-quality protein composition. In the innovation area NewFoodSystems, the reKultI4Food project also follows this approach and aims to optimize the processes to make them economically competitive. The Competitive Insect Products project, on the other hand, is looking not only at the protein content of insects but also at possible applications for their fats. For example, olefins could be obtained from insect larvae as biobased and biodegradable high-performance lubricants.

Residual material streams from the food industry, provided they are not processed into animal feed, should instead be refined into high-demand chemicals. For some time, there has been an approach to process old cooking oil residues into biofuels, for example kerosene. PHABIO's goal is more ambitious. Here, those involved want to use bacteria to produce the biodegradable plastic polyhydroxybutyric acid from animal waste fats from slaughterhouses - in a process that is as sustainable and economical as possible.

The target product of the BranLact research project is lactic acid, the raw material of the important biodegradable bioplastic PLA. Together with a Chinese project partner, the research team from the Leibniz Institute of Agricultural Engineering and Bioeconomy used defatted rice bran, a residual material from rice processing, for this.

The TaReCa project revolves around leftover peppers. A harvested bell pepper plant is up to three meters high. From this extensive biomass, basic chemicals such as various sugars and polyphenols can be extracted in a biorefinery. In an intermediate step, secondary plant compounds can also be isolated. Specifically, the project is interested in the flavonoids cynaroside and graveobioside A. The former is of interest to the cosmetics, food and pharmaceutical industries, while the latter is an insecticide suitable for crop protection.

The BioLyte project addresses the increasingly important energy storage devices - batteries and accumulators. The electrolytes they contain are often not environmentally friendly or sustainable. As biobased alternatives, the research team intends to use plant anthraquinones on the one hand and flavonoids also derived from plants on the other. These compounds are to be obtained from residual and waste streams from the food and animal feed industries.

Another place where residual biomass streams are generated is in mills. The EcoWashCycle project is developing a process to produce customized enzymes, soaps and biosurfactants from wheat bran and husks in a waste-free biorefinery as ingredients for ecologically certified detergents and cleaning agents. Biorefineries are also the focus of the CichOpt and ProWaste projects.

Platform chemicals from leftover chicory

In ChicOpt, the researchers plan to produce platform chemicals such as hydroxymethylfurfural from beets and roots of chicory species on a pilot plant scale. The furfural is used in particular for the production of bioplastics.

In ProWaste, proteins and dietary fibers are to be extracted from food industry by-products of different compositions in a biorefinery in order to use them as high-quality nutrients for other food or feed products. Possible side streams for this could be rapeseed press cake, oat bran or brewer's grains.

And there are more residual materials from the food industry that may be suitable again as a raw material for food. Knärzje, a bread beer, is already on the market. The Frankfurt-based startup uses organic bread scraps as the basis for the fermentation process, which is why it calls it "zero-waste beer." The CocoaFruit project, on the other hand, is still in the research stage (read more in this multimedia episode). Here, researchers are aiming to make holistic use of the cocoa fruit, only one-tenth of which is often used for cocoa today. However, the aromatic pulp and shell of the cacao fruit could become innovative foods and ingredients: Mushroom mycelium could be grown on the cocoa fruit skin to produce a protein- and fiber-rich food ingredient. After certain processing steps, the pulp could be used as a raw material for fruit preparations and beverages.

Municipal waste streams will play an important role in the bio-based circular economy because large volumes of different biomass residual streams converge there - from biowaste to green waste to wastewater. The latter contain large amounts of nutrients - so many that they need to be degraded to prevent pollution of aquatic ecosystems. Precisely this is the goal of the Hypowave and SUSKULT research projects.

In Hypowave, researchers have shown that the use of recycled wastewater can reduce the high water consumption in agricultural production and that nutrients such as phosphorus and nitrogen recovered from the pretreated wastewater can be used for the production of lettuce - but probably also for various vegetables and ornamental plants. SUSKULT - a collaborative project from the Agrarian Systems of the Future funding measure - is building a demonstration plant at a wastewater treatment plant on the Emscher River that will produce vegetables on a ton scale in greenhouses in the medium term. The sewage treatment plant supplies the indoor farm with nutrients, carbon dioxide, heat and water.

The participants in the DemoBioBZ project want to obtain not nutrients but energy from wastewater. To this end, the researchers have developed a biofuel cell that can be used to generate electrical energy directly from organic material such as wastewater. In the Gülle-2-Laub project (Manure to leaves), liquid manure is combined with shredded leaves from municipal collections to create a recycled fertilizer. The effect is that the slurry in this form leaches less nitrate into the groundwater while loosening the soil and improving its quality. A corresponding pilot plant is already under construction.

Thematically broad, but with the idea: small rather than large and therefore flexible - that is the approach of the FLEXIBI project. It will provide a decision-making tool for implementing efficient and sustainable processes in small-scale biorefineries. The aim is to be able to consider individual solutions for municipal waste streams as well as for agricultural residues, based on the local availability of the respective biomass.

In addition to its importance as an energy source, crude oil has played a role primarily as a raw material for the plastics industry. By no means all plastics can be efficiently and sustainably recycled or are rapidly biodegradable. Therefore, waste streams are also generated here, which should be used as raw materials as far as possible in the sense of a circular economy. Incidentally, this challenge also applies to biobased plastics. After all, the goal of replacing all fossil raw materials used today with biobased alternatives also means that these biogenic resources must be used efficiently: The amount that can be sustainably formed per year is limited.

Breaking down plastics with the aid of enzymes

Since microorganisms can use many different carbon sources as food, some are able to degrade plastics for their metabolism. In the EU-funded collaborative project P4SB, the researchers want to use synthetic biology methods to optimize the bacterium Pseudomonas putida so that it can degrade the petroleum-based plastic PET or polyurethane (PU) and, at the same time, produce the basic building blocks for a bioplastic - so-called polyhydroxyalkanoates.

The European-Chinese research project MIX-Up also aims at the circular economy of plastics. The main goal is to eliminate the sorting process, which has made recycling costly up to now. With the right enzyme mix, the unsorted plastics are to be broken down into their building blocks. These building blocks will then serve as food for microorganisms in a bioreactor, which in this way will produce new valuable materials - for example bioplastics. To this end, the project participants not only want to use naturally existing metabolic pathways, but also develop completely new biological processes.

From exhaust gas to raw material

Last but not least, the greenhouse gas carbon dioxide (CO2) is often produced in industry as a waste or side stream. Some processing operations fall within the scope of the bioeconomy, as numerous microbes can use carbon dioxide as a raw material to form higher-value chemicals.

The BMBF supports these efforts within the framework of several funding initiatives, including "Chemical processes and material utilization of CO2". A new funding measure on biobased CO2 utilization was recently launched. The Kopernikus projects, whose aim is to drive forward the energy turnaround, are also conducting research on this topic. The P2X project, for example, is looking at how green hydrogen and CO2 can be converted into polymer building blocks that the chemical industry urgently needs, and how microorganisms can be used to convert CO2 on an industrial scale into chemicals that provide the cosmetics industry with basic materials for care products.

The Fraunhofer-Gesellschaft conducts cross-institute, application-oriented projects on the question of how carbon dioxide from industrial waste gases can be recycled using microbial fermentation processes. The Evobio project, for example, focuses on wastewater treatment plants in order to close material cycles and recover CO2 as well as nutrients and put it to direct material use. The ShaPID research project aims to use CO2 and biogenic raw materials to produce new polymers for the plastics industry. New and cost-effective approaches are the focus of the CELBICON project. Here, researchers combine the absorption of CO2 from the air with electrochemical CO2 conversion to carbon-based intermediates and a final microbial fermentation of these intermediates to produce higher-value chemicals.

With biogenic raw materials to a sustainable, circular economy - this is one of the two guidelines of the German government's National Bioeconomy Strategy. It aims to map nature's carbon cycle in a future bio-based industry. It is not simply a matter of replacing fossil resources with renewable raw materials. Rather, the aim is to exploit the potential inherent in biomass much more effectively through cascade use and to develop the resulting material flows in a resource-efficient and sustainable manner for different branches of industry. Whenever competing uses arise, food security always takes priority.

The Strategy for Research for Sustainability (FONA) and the German Sustainability Strategy also emphasize the role of more efficient use of biomass residue streams. At the European level, the European Bioeconomy Strategy and the European Green Deal pursue numerous approaches towards a resource-efficient and circular economy.

Network activities from the economy

Science and industry have also long since established initiatives and networks on the path to a circular economy.

The Federation of German Industries has founded the Circular Economy initiative. In the Rhine-Ruhr region, an association is driving forward a regional network characterized by innovative companies from all over the world, the Circular Valley. A German-Dutch Interreg association has launched the Circular Bio network. Biorefinery operators, for whom resource efficiency has always been a core concept, are also increasingly relying on residue-free processes, as in the Elbe-NH project, and on the principle of the circular economy by using biogenic residues and waste materials as raw materials, as in the Fraunhofer CBP plant in Leuna or the planned plant on the BioCampus in the port of Straubing-Sand.

The concept of the zero-waste city makes it clear that waste recycling is not just about technological processes: residual materials and waste streams must be collected, processed and marketed. Municipal collection of recyclables is likely to become increasingly important in this context. More than 400 European municipalities have now joined the Zero Waste Initiative, including Munich.