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Environmental & Energy Systems

Valuable kitchen waste

Researcher:  Dr. Ina Körner, Steffen Walk

Institute: Wastewater Management and Water Protection

School: Civil Engineering (B)

The production of biomethane from kitchen waste offers an as yet untapped potential for the energy transition. So far, only a small portion has been used for this purpose.

Of 85 kilograms of kitchen waste generated in private households per person and year, only about 21 kilograms is collected via the organic waste garbage can so far and used for further recycling into biogas and compost. "In order to generate biogas from kitchen waste, the waste must be properly separated. A large part of kitchen waste mistakenly ends up in residual waste and is thus incinerated and lost for high-quality energy and material recycling," explains Steffen Walk. He is part of the Bioresource Management (BIEM) research group at the Institute of Wastewater Management and Water Pollution Control at the Hamburg University of Technology, which has set itself the goal of recycling biowaste with a project. Up to now, in many places, biogas has not yet been obtained from the portion that goes into the organic waste garbage can, but only compost is produced. Ideally, there should be a process cascade of biogas production followed by composting of the so-called fermentation residue for efficient energy and material use of the biowaste. Biogas contains mainly methane and carbon dioxide. By removing the carbon dioxide, the biogas can be upgraded to biomethane, which has a similar calorific value to fossil natural gas.  "Only about 15 percent of Germany's 120 or so municipal biogas plants operate according to this principle and feed biomethane into the natural gas grid, while the others directly convert it into electricity. So there's still room for improvement," Walk said.

Covering gas consumption for a year

If the biowaste potential of all 83 million inhabitants in Germany were used to produce biomethane, the gas consumption of 2.8 million people could be covered for a year. We can all contribute to this by separating kitchen waste better. The use of small containers with lids is recommended for separating organic waste in the kitchen. Compared to plastic or paper bags, this saves resources and is easy on the wallet. The more that is collected, the greater the incentive for new construction and upgrading of compost and biogas plants for biomethane production. Steffen Walk demands: "Politicians should also demand kitchen waste separation more consistently. Separation rates of 65 percent, equivalent to 55 kilograms per person, are definitely possible." A start here would be the consistent installation of organic garbage cans for all households. So far, only just under 60 percent of German households have an organic waste garbage can.

Project Circular Economy

In order to give people a practical understanding of waste separation and recycling, Steffen Walk founded the "BioCycle" project. "BioCycle" describes the interrelationships of a cycle in which food becomes waste and then becomes new products, such as biogas or compost and soil fertilizer. The idea is that not all waste is avoidable. "You have to throw away a banana peel, but, disposed of properly, it can close the biocycle" explains Walk. In times of scarce energy and degradation of soils due to their over-intensive use, this problem can be counteracted with a circular economy. Biocycle is conceived as a learning opportunity, designed in six stages to show the cycle of food.

The project is also integrated into the "mudflat walks" organized by the Hamburg Open Online University (HOOU). The concept includes hiking or "driving" through places in Hamburg where renewable energies are produced.

More Information

The Tidal Elbe in a changing climate

Researcher:  Prof. Peter Fröhle

Institute: Wasserbau

School: Civil Engineering (B)

How can the consequences of storms and rising water levels in the tidal river Elbe, resulting from climate change, be minimized? This is what the TU Institute of River and Coastal Engineering is investigating for several time frames up to 2200.

"Without flood protection, large parts of northern Germany would already be flooded today," is how Professor Peter Fröhle sums up the situation. This applies not only to the coast from Husum to Wilhelmshaven; high water levels and storms would also change the appearance of the landscape between Hamburg and Brunsbüttel. The areas along the tidal Elbe, which is characterized by high and low tides, would be almost impossible to settle without flood protection with dikes and protective walls. But estuaries like the Tidal Elbe were and are lifelines for the hinterland. Settlements, towns, companies and ports have grown up along these estuaries and in many cases have ensured prosperous economic development. These, as well as the valuable biotopes and ecosystems, must be protected and preserved in the future.

The effects of climate change on this area and which possible flood protection measures would make sense in the future are being discussed in the TideelbeKlima project at the Institute of Hydraulic Engineering at the Hamburg University of Technology, initially from a hydraulic engineering and water management perspective, and evaluated from a geotechnical perspective by the Institute of Geotechnical Engineering and Construction Operations. The Institute for Geo-Hydroinformatics analyzes the effects with regard to groundwater levels and possible salinization of the groundwater. Subsequently, the ecological and economic analyses and evaluations are carried out. At the end there should be concrete options for action. The tools, methods and evaluation schemes developed are to be prepared in such a way that they can also be applied to other German estuaries such as the Weser.

Sea levels are rising

Without sufficient protection by dikes, walls and flood plains as well as barrages and drainage structures, storms and floods would cause enormous damage. This has been painfully demonstrated time and again in the past. "As a result of climate change and the associated rise in sea level, storm surges will accumulate much higher in the future for the same storm intensity. Water levels that used to occur on average once every hundred years will then also come upon us much more frequently, for example every five years. In addition, storms may become even more intense as a result of climate change, which would then further increase the extreme water levels," says Fröhle, the institute's director. The TideelbeKlima project therefore wants to define protection lines to form safe zones that can withstand higher mean water levels and more frequent floods. In addition to dikes and flood protection walls, there are a variety of concepts to protect against flooding. These range from adapted construction methods and the creation of more space for water to dams or barrages that can prevent a flood wave from entering.

Raising dikes, reinforcing protective walls

Just a few decades ago, experts assumed that the average sea level would rise by 25 centimeters in a hundred years. Climate change is having an accelerating effect, so that sea levels are now expected to continue to rise by one meter per century. Every ten years, planned flood protection targets and measures are re-evaluated so that protection measures can be adapted if necessary. In the current construction program for the Hanseatic City of Hamburg, for example, it is planned to expand dikes and flood protection facilities to a height of at least 8.30 meters above sea level.

One measure is to keep water out, another is to give it more room to flood. Especially on the coasts, such polders can serve as retention areas to prevent water from causing further destruction. "Ultimately, flood protection can even go as far as dredging areas that have already been diked. In the area of the Tidal Elbe, however, the effectiveness of such measures from a hydraulic engineering point of view is comparatively low," explains TU scientist Fröhle. Quite the opposite is true of the extremely costly but effective measure of erecting a barrage. This has already been done for the neighboring smaller Elbe tributaries, such as the Este or the Krückau, and the Eider, which flows into the North Sea. If such a structure were built on the Elbe, however, it would be several kilometers long and much larger and longer than the existing barrages. Its construction would cost billions of euros. The advantage would be that storm surges could be kept out of the Elbe and damage avoided from the outset.

In addition to the Institute of River and Coastal Engineering at TU Hamburg as coordinator, the TideelbeKlima project also involves the TUHH-Institutes of Institute of Geotechnical Engineering and Construction Management and Geo-Hydroinformatics and the Institute of Geoecology at the TU Braunschweig and the Institute for Ecological Economy Research (IÖW) in Berlin.

Energy storage in the basement

Researcher:  Nico Weiß
Institute: High-Frequency Technology
School: Electrical Engineering, Computer Science and Mathematics (EIM)

Hydrogen is a promising energy carrier, but explosive and difficult to store. But with a new method, households can even produce and store the gas without it becoming dangerous.

On the table are five small vials filled with a viscous liquid ranging from almost transparent to a strong yellowish color. The special thing about this liquid is that it can hold hydrogen. The darker, the more hydrogen atoms it contains. "With the help of a measuring device called a resonator, I can determine the hydrogen content. I do that by measuring the electrical propagation capability in a vibrational field. The resonator tells me what percentage of the carrier medium is loaded with hydrogen," says project manager Nico Weiß, explaining his activity and the idea of using this method to use hydrogen on a larger scale for domestic use. Hydrogen is a gas, therefore requires a lot of volume and can only be stored efficiently with great effort. It is usually stored under high pressure or in liquid form in tanks. The good thing is, by means of wind or solar power, hydrogen can be produced regeneratively and can be used well as a CO2-free fuel for drives. However, due to the potential danger under the Compressed Gas Ordinance, the use of hydrogen to generate heat in homes has so far only been permitted to a limited extent.

Inert like diesel

At Hamburg University of Technology, research is being conducted on an alternative in which households can generate and store hydrogen themselves without it becoming dangerous. Nico Weiß explains why: "The hydrogen atoms are chemically bonded in the process. The main role is played by hydrocarbons, so-called LOHC - Liquid Organic Hydrogene Carriers. This is a synthetic substance that is predominantly produced from petroleum." The idea is that hydrogen atoms can dock onto the organic molecules of LOHCs and be released when needed. White is a research associate at the Institute for High Frequency Technology (IHF). He points to the variously colored vials. "In this storage form, the highly reactive hydrogen becomes tame to the touch and inert, somewhat like diesel oil," says Nico Weiß, describing the process. Via a temperature-controlled reaction, the hydrogen can be separated from the LOHC again and reused in gaseous form.

This process is based on the basic idea of generating a house's energy requirements CO2-free. First, by using a photovoltaic system on the roof to generate electricity, which then uses electrolysis to separate water into its constituent hydrogen and oxygen. For a household, the idea then functions as a heat and energy storage concept. The LOHC is reusable and can probably be charged and discharged up to 1,000 times. "Old petroleum tanks, for example, which can still be found in many basements, serve as storage tanks," says Weiß. Sounds simple and practical. Once the LOHC is old and used up, it can be replaced with the help of a tank truck. "You can think of it like a circular pledge system," explains Weiß, providing a non-hazardous way to store energy. In this way, the regeneratively generated energy can be consumed when it is needed. Even if you come into contact with the oily substance, nothing happens; it is non-toxic.

Increasing efficiency

Currently, one challenge with this concept is determining the hydrogen loading of the LOHC in the process. And this is the task that IHF and Nico Weiß have taken on in the VisPer project. "Because only if you know how much hydrogen is stored in the LOHC can you control the reaction rate and realize efficient storage and release," explains engineer Weiß. Together with the Chair of Process Machinery and Plant Engineering at Friedrich-Alexander-Universität Erlangen-Nürnberg (FAU), he is researching the sensor concept based on the interaction of LOHC with electromagnetic waves in the VisPer project funded by the German Research Foundation (DFG). So far, the efficiency is 30 to 40 percent, but LOHCs can store hydrogen for a long time. Disadvantage: Even though the "loaded" LOHC can be stored well, a relatively large amount of it is needed. One kilogram of carrier fluid contains a maximum of 6.2 percent hydrogen.

In the long term, the idea of "refueling" LOHC with hydrogen can also be transferred to other applications. For example, there are offshore wind farms equipped to convert the green electricity produced there directly into hydrogen. "Stored in LOHC, the hydrogen could be transported by ship to a terminal," says Weiß. Again, a sensor will help measure the degree of filling of the LOHC. "We have now reached the next stage with our sensor research. We are still in the planning phase. After that, we'd like to build a prototype of how it could actually be used in a single-family home." And perhaps soon the first households will generate and store their energy in this way.

VisPer is the name of the project in which TU Hamburg is collaborating with Friedrich-Alexander-Universität Erlangen-Nürnberg (FAU) to research a sensor concept for alternative hydrogen storage based on the interaction of hydrocarbons with electromagnetic waves.


Agriculture - ecological and sustainable


Researchers                 Prof. Ralf Otterpohl

                                     Dr. Tavseef Shah

                                     Durga Prasad Babu Nasika

Institute                        Wastewater Management & Water Treatment

School of Studies         Civil Engineering

Funding                         Private, TUHH & FHH Hamburg

By 2050, the global water demand is expected to increase by 55 percent, much of which is attributed to agriculture. No wonder, since a good 40 percent of all food worldwide is grown on artificially irrigated land. Any savings in agricultural water use can free up water for other pressing needs like drinking water. A TU Hamburg-project shows how water and fertilizer use can be drastically reduced with a new cultivation concept.

Peas, beans, potatoes, and rice. Agriculture feeds us, but it pollutes groundwater with “unhealthy” nutrients especially nitrates and a variety of biocides. These are used in farming to control the growth of harmful organisms. But that also makes them potentially dangerous to humans, the environment and other organisms beneficial for plant growth. At the same time, agriculture worldwide uses about 80 percent of all freshwater withdrawals. Of this, about 40 percent is used in rice cultivation alone. This is a trend that has been going on for a long time. In the densely populated regions of South and Southeast Asia in particular, huge investments were made in additional irrigation systems between the 1960s and 1980s in order to keep increasing yields.

Dr. Tavseef Shah, with the help of his team from Hamburg University of Technology, has tried out new cultivation methods on site and in field trials in Kashmir in northern India. His idea is to significantly improve the dry rice cultivation (System of Rice Intensification, SRI) propagated mainly by Cornell University in the USA. At Hamburg University of Technology, he developed an intercropping concept that involves the simultaneous cultivation of different crops in one field. He combined SRI rice with bush beans. In this way, the nitrogen requirements of the rice plants could be supplemented with the help of the beans, which bind it to their roots. If this type of cultivation were used worldwide, it would save about 20 percent of the world's water needs as well as some of the fertilizer requirements.

And the bush beans provided an additional effect: the weeding requirement, which is otherwise very considerable for dry rice, fell by about 70 percent. Shah expanded his research even further for this purpose and founded the “Environmental Robotics” working group last year in 2021. In parallel with the development of rice cultivation in Kashmir, the group invented and built a selective weeding robot that has automatic plant recognition and is thus able to mechanically remove only the weeds that are harmful to the crops without chemicals. This development is in prototype status and is led by doctoral student Mr. Durga Nasika.


3 Questions for Dr. Tavseef Shah of the working group Environmental Robotics at the Institute of Wastewater Management and Water Protection about the project:

How does intercropping work, alternating rice and bush beans?

In intercropping, we plant rice and beans together in one plot. The beans are sown between the crop rows two weeks after the rice is sown. Since we use the dry rice cultivation method, the beans find good growing conditions. We have tested this method in fields in Kashmir with success. We observed reduced weed infestation, better and more diverse crop yields, and thus diversified income streams.

How much water can be saved with dry farming?

The SRI method can save up to 40 percent water in rice cultivation. We have observed this time and again in our trials at the TU Hamburg and in our field trials in Kashmir. We have to consider that on average 5,000 liters of fresh water are consumed to produce 1 kilogram of rice using the conventional flood rice method. Even if this method is slow to spread, the water savings will be significant. With intercropping, the dry rice cultivation method provides an added incentive to the farmers and the environment! We are currently looking at the possibility of using this methodology to grow rice in saline soils.

What has been the reaction of farmers to the weeding robot?

The farmers we talked to here in northern Germany were really excited about such an agricultural aid that eliminates weeds without the use of agrochemicals. For them, it's the kind of environmentally friendly and cost-effective solution that they're hoping for from a technical university. The idea was initiated by Prof. Otterpohl and Mr. Nasika has been working on this project since the very beginning.

Coupling energy networks - concept for tomorrow


Researcher             Prof. Christian Becker

                              Prof. Arne Speerforck

                              Prof. Kathrin Fischer

                              Prof. Volker Turau

Duration                12-2019 – 11-2022

Institute                 Electrical Power and Energy Technology

                              Engineering Thermodynamics

                              Operations Research and Information Systems


School of Studies   Electrical, Engineering, Computer Science and Mathematics (E)

                               Process and Chemical Engineering (V)

                               Management Sciences and Technology (W)

Global climate targets call for rapid decarbonization of energy generation and increasing integration of renewable energies. But the wind doesn't always blow or the sun doesn't always shine. To ensure a secure supply, electricity, gas and heat grids must be coupled.

On the one hand, the energy system of the future will be determined by the increasing electrification of the consumption sectors of transport, industry, commerce and households. On the other hand, the volatility of renewable energy generation and the different dynamics of energy consumption require a high degree of flexibility and thus energy storage capacity of the overall system. This is the only way to ensure a resilient energy supply. It succeeds when the systems and networks of the energy carriers electricity, gas and heat are coupled with each other. And at the same time, intelligent networking takes place to control the plants, generators and consumers of the energy system. The idea is to convert energy flexibly between the energy carriers according to demand, for example, to convert energy from renewable electricity production into another form of energy, store it on a larger scale and convert it back into electricity when needed.

Ensuring grid stability

An example of such coupling effects is the use of cogeneration plants that feed energy into both the heat and electricity grids. For example, if there is a high demand for heat and at the same time a large supply of electrical energy, these plants cannot be down-regulated to ensure that the heat demand is met. This may result in less power being fed in from renewable energy sources such as offshore wind farms to ensure the stability of the electrical power grid. The transient, i.e. temporary, consideration also creates the possibility of creating a temporal balance through the targeted use of storage technologies. These considerations can also be used to answer the question of what type of storage, in what size, and at what location are sensibly deployed.

Reliably integrating renewables

Based on different scenarios using the model just described, we will look for ways to reliably integrate renewables into an existing energy supply structure. The final evaluation of the different scenarios is based on the CO2 emissions per year, which allows a direct conclusion on the goals of the energy transition. The results of this research contribute to securing society's growing energy needs and to the greatest possible environmental and climate compatibility.

Example projects with TU Hamburg participation:

TransiEntEE: Transient behavior of coupled energy grids with a high share of renewable energies, ResiliEntEE: Resilience of coupled energy grids with a high share of renewable energies, CyEntEE: Cyber Physical Energy Systems - Sustainability, Resilience and Econimics, funded as I³-Lab of TU Hamburg, EffiziEntEE: Efficient integration of high shares of renewable energies in technical-economic integrated energy systems, iNeP in NRL: Integrated Network Planning of the Sectors Electricity, Gas and Heat in the North German Real Lab.