Last one cleans up the earth

How to deal with the garbage problem on earth?

We separate our household waste, prefer deposit bottles to disposable ones, and avoid plastic packaging. Even though many people have already changed their thinking, too much waste is still produced and too little recycled – with fatal consequences for people and the environment. According to the German Environment Agency, 230 kilograms of packaging waste were produced per capita in this country alone in 2018, of which around 40 kilograms were plastics. Supposedly for further recycling and processing, plastic waste is exported – not infrequently to countries with barely existing environmental standards – and ends up in the world’s oceans by the ton. To date, more than 8.3 billion tons of plastic have been produced, much of which has never been recycled and will not be in the future. Forecasts predict an accumulated plastic waste volume in the environment of twelve billion tons by 2050.

It is not only politicians who are trying to get to grips with the problem, which has long been a global one. Researchers are also looking for ways to eliminate or use waste sustainably. “Our topic is clean water, which is a vested human right according to a UN resolution from 2010, but is still not realized – especially globally,” explains Prof. Dr. Marcus Halik from the Department of Materials Science and Engineering. Together with his team, Halik has spent the past few years at FAU researching how smart rust can be used to remove plastic from water. To this end, the researchers have developed new materials and a concept based on them that makes it possible to efficiently capture highly problematic water contaminants magnetically using special nanoparticles. The developed nanoparticles bind contaminants and can be easily magnetically collected together with them. “The materials are inexpensive, non-toxic, recyclable, can be produced in large quantities and thus allow the removal of contaminants in all relevant concentration ranges, from oil spills to the smallest glyphosate contaminants,” Halik says.

Generate energy with waste

The smart grate has already proven itself scientifically in the removal of nano- and microplastics, liquid hydrocarbons such as benzene or petroleum, weedkillers or toxic chlorine compounds from rivers, lakes or the sea. “We are currently developing the transfer of the concept to contaminants such as hormones or drug residues, as well as the so-called PFAs,” explains the materials scientist. PFAs, polyfluorinated alkyl substances, are a large group of chemical compounds used in lubricants and impregnating agents that are very common. Just how promising Halik’s research projects are is also shown by the fact that they are funded by the German Research Foundation and the German Federal Environmental Foundation.

Another approach to tackling the problem is called “waste-to-energy,” the environmentally friendly utilization of waste for energy. Generating energy from waste is now standard practice in waste incineration and biogas plants. In Germany and other countries with developed waste management systems, waste is therefore of great importance for the supply of electricity, heat and process energy. The European Waste Framework Directive ranks this energy recovery of waste fourth in its waste hierarchy, behind waste avoidance, preparation for reuse and recycling. Much of the waste is incinerated. However, especially in the case of regenerative raw materials from biomass, this is only the very last step. Increasingly, the principle of cascade utilization is being pursued, in which the biomass is first to be recycled as long and as often as possible. Especially in decentralized processes, energy recovery can also be achieved by means of non-thermal technologies.

Garbage, too, can be of value

Prof. Katharina Herkendell is conducting research on so-called bioelectrocatalysis at the Chair of Energy Process Engineering. This involves the low-emission energetic residual use of waste materials by means of enzymatic and microbial catalysis in electrochemical cells: Biological materials are thus used as catalysts in electrochemical processes. “In biofuel cells, for example, we generate green electricity from the oxidation of organic compounds such as those present in regular household waste, in biofluids or in wastewater. This is also called waste-to-energy,” the scientist explains. Furthermore, it is also possible to practice bioelectrochemical “power-to-X”, i.e. pumping the generated renewable surplus electricity from solar or wind power into an electrosynthesis, in which the electrons energetically upgrade residual streams of carbon dioxide, for example. Here, with the right biocatalyst systems, a valuable material synthesis of, for example, biomethane, -methanol or other e-fuels can be operated. The main goal is always to maximize the use of energy sources in material cycles that are as closed as possible, i.e., to contribute to a circular bioeconomy, Herkendell says, because “our waste is still valuable.” Here, research into recycling in enzymatic systems is still in its infancy.

To date, enzymatic biofuel cells have been used primarily in medical technology, where they have a wealth of applications. Microbial systems in biogas plants and sewage treatment plants, where electrochemical elements are already being successfully implemented in pilot studies, are considered more feasible and established for the energetic use of residual materials. “In general, the research field is still quite young, lacking long-term stable and scalable systems as well as techno-economic studies. So it is not yet possible to make any generally valid statements about the profitability of these energy systems. In the long term, the combined systems of renewable catalyst materials and green electricity have captivating advantages in decentralized energy process technology,” Herkendell explains.

When enzymes eat garbage

Enzymes are also used at the Chair of Biochemical Engineering (BVT) to decompose waste, or more precisely, plastics such as polyethylene terephthalate (PET). We associate this primarily with plastic bottles. But PET causes problems even in the smallest denominations and threatens the environment. The deposition of macro- and microplastics is dangerous not only in waterways, but throughout nature. Most plastics are highly persistent and therefore cannot be degraded in a definable period of time. “To counteract accumulation of plastic waste in nature and to save resources for the production of new plastic materials, increased recycling or ideally the complete degradation of plastics is necessary,” explains Stefanie Fritzsche, a research associate in the Department of Chemical and Bioengineering (CBI). There are enzymes in various microorganisms that are basically able to break down polymers such as PET. The natural function of these enzymes is to attack the waxy protective layer of certain plants. “However, it has so far proved disadvantageous that the reaction rates of the natural enzymes with the non-natural PET are comparatively low, and so degradation takes a very long time, complete degradation is not possible, or the use of large quantities of enzymes is necessary, making the processes uneconomical on a large-scale. Therefore, the focus of our research is to improve the activity as well as the stability of these enzymes by so-called protein engineering,” explains the scientist.

In protein engineering, the DNA coding for the enzymes is modified to optimize their desired properties in such a way that large quantities of plastics can be degraded within the shortest possible time spans. This is forward-looking for waste management: a French company has already been able to show that large-scale application of this recycling strategy is also possible. “At the Chair of Bioprocess Engineering, with its interdisciplinary orientation and fully equipped molecular biology laboratory, the basic research of protein engineering on a molecular biological basis can be combined with actual biotechnological implementation,” says Fritzsche, whose first research project phase was supported by the Alfred Kärcher Förderstiftung.

The willingness to change

But can science ever get to grips with the waste problem despite even the most generous and targeted funding? For Professor Halik, one thing is certain: “We can make a contribution to this with our method – in particular to reducing new pollution by removing pollutants from the water. Of course, no technical process is suitable for cleaning the entire 1.4 billion cubic kilometers of water on earth from micro- and nanoplastics or other pollutants. However, the technical implementation of magnetic water purification offers the possibility of minimizing future pollutant inputs, which are essentially via rivers.” Ultimately, Marcus Halik believes, in a global context, only a paradigm shift can lead to success when it comes to combating waste: “The very use of the word ‘wasteʻ implies our admission of failure, because there is de facto no waste. All things consumed come from natural resources and are thus transformed recyclables – this even applies to CO2. Resource-neutral economies and living through complete material cycles and energy-efficient processes seem to be the only models for living in a truly sustainable way.”

Researcher Herkendell sees consumers in particular as voters with a responsibility: “It is dawning on many people that we are facing some uncomfortable changes when it comes to sustainable consumption. The issue is getting more and more attention. We need to invest where we can in research that offers long-term economically attractive alternatives to today’s waste production and recycling.”

For Stefanie Fritzsche, the fact that there are now many research groups working on this issue and attacking it at very different points is crucial: “While some research approaches focus on avoiding the creation of waste, for example by developing new types of materials or processes, other research groups like us try to efficiently break down waste that has already been created. Although the waste problem seems insoluble at the moment, I therefore think that the issue can be contained in the future through more conscious behavior on the part of humanity as well as scientific progress in particular.”

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