Hamburg Wasser: Technical Managing Director on water reserves, investments and challenges in wastewater treatment

Since April, Martin Gerhardt has been responsible for important areas of the municipal utility as technical managing director of Hamburg Wasser. He previously worked in the wind power industry at Siemens Gamesa. In the interview he talks about Hamburg's reserves in dry times, rising prices, errors in the VERA sewage sludge incineration plant and substances in the wastewater that will remain there forever if a fourth treatment stage is not introduced.

WELT AM SONNTAG: Mr. Gerhardt, in dry summers, cities and water suppliers elsewhere call on people to stop watering their gardens. Why does Hamburg not yet have such restrictions?

Martin Gerhardt: Hamburg is fortunate in that we have very deep and rich aquifers. Added to this is the technical performance of the waterworks and the network. We can currently cover a peak demand of around 460,000 cubic meters per day. We have not reached this limit in the past. That's why we haven't had to declare an emergency situation yet.

WAMS: This year, consumption on individual hot days was around 420,000 cubic meters. Is that still a comfortable distance?

Gerhardt: That's still some way from our capacity limit, but it's already on a scale that we don't want to have in the long term. Sometimes the holidays help us because there are fewer people in the city. The very warm June was also surprisingly wet, with several heavy rain events. This reduces the need for garden water, for example. If we had experienced three more very dry weeks with many hot days, the situation could have been different.

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WAMS: Hamburg's aquifers sometimes only react after years to dry or rainy years. Could today's hot summers become a problem later?

Gerhardt: No, not exactly, as long as there are always rainy years and, above all, wet winter months. Some aquifers are up to 420 meters deep, others 250 or 300 meters deep. The rain arrives there more slowly but also more evenly than at surface aquifers. Climate forecasts assume that the average precipitation in our region will not change fundamentally even with further warming. This is initially a good signal. We do not currently see a threat situation for Hamburg like in other regions. However, the pressure can increase seasonally. That's why drinking water is a very valuable resource for us, which we have to use sustainably and carefully, especially during peak times.

WAMS: Hamburg is growing. Are the existing capacities sufficient for a larger population?

Gerhardt: According to our calculations, Hamburg will need around four million additional cubic meters of water per year by 2050. That's why we want to increase our peak capacity to 500,000 cubic meters per day by the early 2030s. We don't want to build new waterworks, but rather improve the existing infrastructure.

WAMS: What does that mean specifically?

Gerhardt: The Langenhorn waterworks is a good example of this. Here we are increasing capacity by 43 percent. Measures are also planned at other waterworks. There are also large underground drinking water tanks in which we store water and can thus compensate for peak consumption.

WAMS: Does Hamburg Wasser prepare the storage tanks specifically before known consumption peaks, for example before a football game after which a lot of people go to the toilet at the same time?

Gerhardt: We know the seasonal consumption patterns and the usual peaks, but we cannot react to a single event down to the minute. In total we have a storage volume of around 300,000 cubic meters. This corresponds approximately to the volume of the Inner Alster. The net and container together form a reservoir. Without this buffer, we would have to have significantly larger funding capacities available.

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WAMS: So water shortage is not Hamburg's most pressing problem for the time being. Where is the bigger challenge?

Gerhardt: We have a very high and increasing need for investment in both drinking water supply and wastewater. A large part of our infrastructure was built shortly after the Second World War. These systems and networks are now reaching an age where they need to be renovated. We don't want to wait until expensive failures occur, but rather invest with foresight.

WAMS: What sums are we talking about?

Gerhardt: We want to invest 1.1 billion euros by 2029. Around 64 percent of this comes from the wastewater sector, the remaining part from the drinking water supply. In addition to the renewal of old infrastructure, there are new requirements: further treatment of wastewater, sewage sludge incineration, phosphorus recovery, the protection of critical infrastructure and our climate protection goals. Systems must be better protected physically and digitally, and buildings and vehicles must gradually become climate neutral.

WAMS: Does this make water and wastewater more expensive for Hamburg residents?

Gerhardt: Part of these investments will be reflected in fees and prices in the long term. However, our goal is not to achieve the highest possible profit at the expense of the citizens.

WAMS: One of the most expensive and difficult projects concerns the VERA sewage sludge incineration plant. What is the status there?

Gerhardt: VERA remains a very challenging project. Actually there are two sub-projects. The first is to expand the facility with a new building. Most of the major components are now installed there. We are working on the piping and cabling, then cold commissioning should begin. We are making progress, but the path remains difficult and the project still has risks. The other concerns the renovation of the existing lines.

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WAMS: The construction site is now 42 months behind the original schedule. What went wrong?

Gerhardt: It is an extremely complex project that has to be implemented in a difficult market environment. In addition, the project planning did not go optimally at the beginning. Something like that is difficult to recover at the end of a project. In addition, we are building in an existing facility that continues to operate. Sewage sludge is burned there every day. In this current system, we are renewing one part, while another part needs to be renovated afterwards. This is an extremely complex system construction on a limited area.

WAMS: When should the expansion be ready?

Gerhardt: The expansion is planned for 2028. We are still in the early planning phase of renovating the existing lines and are examining various options. In the first quarter of 2027 we want to have a better picture of what work is necessary and what costs we can expect. According to current plans, the renovation should be completed in 2030.

WAMS: Can you assure the people of Hamburg that the facility will be completed?

Gerhardt: We will definitely complete the VERA. Of course we would have liked things to go faster and more smoothly. But similar systems in other cities are also very expensive and complex. What is crucial is that we now complete the project with good project and risk management.

WAMS: You seem remarkably calm about the delays.

Gerhardt: The situation is what it is. A clear project structure, transparent risk management and open reporting to the supervisory bodies are important to me. Some errors from the initial phase cannot simply be corrected by later additions. You have to stay realistic. I also gained experience with complex systems and crises in the wind power industry. Hyperventilating doesn't help.

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WAMS: There is a second difficult system on the sewage treatment plant site: phosphorus recovery. To this day it is not working as planned either.

Gerhardt: Phosphorus recovery is an absolute pioneering project. We are one of a few locations in Germany where phosphorus recovery has already been built on a large scale and is ramping up. Technical adjustments are not surprising. So far, no one in Germany has managed to operate this process reliably on a comparable scale.

WAMS: What are the technical problems?

Gerhardt: We discovered that not all ash is the same and that it needs to be dosed much more finely than originally assumed. In addition, the corrosive components of the process were sometimes underestimated. Among other things, hydrochloric acid occurs. Therefore, components had to be better lined later. After these modifications, the system is now ramping up again.

WAMS: Will phosphorus recovery ultimately work reliably?

Gerhardt: It remains ambitious to achieve stable operation around the clock and produce large amounts of phosphorus. But our goal remains. In the future, we will have to use the ash resulting from sewage sludge incineration and recover the phosphorus it contains. There are still some hurdles to overcome, but we must achieve this goal.

WAMS: The upcoming requirements also include a new level of wastewater treatment. What should it filter out?

Gerhardt: This so-called fourth cleaning stage involves trace substances that are difficult to break down, including drug residues and very long-lasting chemicals. For this we need an additional cleaning stage that does not yet exist in this form.

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WAMS: Which technology is suitable for this?

Gerhardt: There are different processes, such as membranes, ozone and activated carbon. Which solution is suitable depends on the composition of the wastewater. A combination of several technologies will probably prevail. All have advantages and disadvantages. Membrane technology is developing very quickly, but requires a lot of energy. Activated carbon, in turn, has a significant CO2 footprint.

WAMS: Your predecessors advocated that manufacturers share in the costs of the fourth stage. Do you also think so?

Gerhardt: It is important that the manufacturers also take on some of the responsibility. The European regulation basically provides for this, but there is resistance to this from parts of the industry. In my opinion, it would be fatal to shift the costs entirely onto the citizens. It makes most sense to avoid problematic entries at the source if possible. If manufacturers are given an incentive to use other and more easily degradable substances, it will be more effective than later removing them from the wastewater at great expense.

WAMS: What substances are you worried about?

Gerhardt: Diclofenac is an example. The active ingredient is contained in pain ointments, among other things, and is washed off after application and ends up in the wastewater. Certain sweeteners are also an issue. They are very long-lived, are carried away with wastewater and ultimately end up in the Elbe, where the concentration has been increasing for a long time. This makes it all the more important to start developing and manufacturing products. However, everyone can easily help with other pollutants in our wastewater.

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WAMS: What particularly often ends up where it doesn't belong?

Gerhardt: Wet wipes continue to be one of our biggest maintenance problems. They don't dissolve like toilet paper, they combine with each other and lead to so-called clogging. These actually look like long chains. They can attach themselves to pumps and render them inoperable.

WAMS: And the second problem is fat?

Gerhardt: Liquid fat should not be poured down the drain. It cools down in the pipes, hardens and forms deposits. Pumps, bends and culverts are particularly vulnerable. Over time, such deposits can significantly reduce the pipe diameter. Wet wipes therefore belong in the trash, as does fat as soon as it has cooled down. Correct user behavior saves us a lot of maintenance effort and therefore costs.

WAMS: Does heavy rain exacerbate the problems in the Hamburg sewer network?

Gerhardt: Hamburg has a combined sewer system in which dirty and rainwater are transported together. In addition to the actual sluice network, there are large collectors underneath that can collect significant amounts of water when it rains and transport it to the sewage treatment plant. This infrastructure was planned with foresight over generations, but some of it also needs to be renewed. Our goal is to renovate around 18 kilometers of the network every year.

WAMS: Is that enough to keep the city safe?

Gerhardt: No. Our aim is to keep rainwater where it falls for as long as possible. We have to delay the runoff, unseal areas and create blue-green infrastructure. This relieves the burden on the sewer system and at the same time allows more water to seep away and contribute to groundwater recharge.

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WAMS: However, Hamburg is densely built up and sealed in many places.

Gerhardt: Nevertheless, there is still great potential. Roofs, schoolyards, street spaces and other areas can be designed so that rainwater is not immediately directed into the sewer. This doesn't just solve a water management problem. Green spaces and evaporation cool the environment. Particularly heavily sealed parts of the city become particularly hot on hot days. This is increasingly becoming a health issue.

WAMS: Is Hamburg far enough along with this restructuring?

Gerhardt: Hamburg takes the topic seriously, tries out a lot and is comparatively innovative. Other cities are further ahead in individual respects. Copenhagen, for example, is incorporating water more visibly into the architecture of public spaces. In my opinion, Hamburg is still in the top third.

Editor Julia Witte known as Vedder works in the Hamburg editorial team of WELT and WELT AM SONNTAG. She has been reporting on Hamburg politics since 2011. One of her focuses is Hamburg's public companies.