Walheim sewage sludge combined heat and power plant

An expert survey conducted to determine the expected construction noise during the day has shown compliance with the legal requirements of the General Administrative Regulation for Protection against Construction Noise (AVV Baulärm) in all construction phases, taking into account the noise protection measures.

During nighttime work, such as concrete finishing, the noise rating level is limited to a maximum of 47 decibels based on the A-weighted scale (dB(A)) in compliance with noise protection measures applicable to residential areas under planning law. According to current case law, no health hazard is expected from construction noise at night, even without noise protection measures.

The construction phase (building work and commissioning) will last about three years, depending on approval processes.

A comprehensive noise forecast has shown that the noise generated in the course of operating the plant complies with all legal requirements. The noise emissions are at least six decibels (dB) below the maximum limit laid down by noise control regulations (TA Lärm).

Various noise protection measures are being taken to comply with the permissible limits, including the installation of a noise barrier for the container handling zone

The plant will operate around the clock. The sewage sludge is scheduled to be delivered from Monday to Friday between 6 a.m. and 8 p.m. There will only be Saturday deliveries after public holidays – as is the case for the garbage collection, for example – or in exceptional cases.

The plant is safe because it has been designed in compliance with all legal regulations to ensure safe operation. Various expert reports consider fire, explosion and flood protection scenarios, and the system is built and operated accordingly:

• In the event of faults affecting air quality, operations at the plant are temporarily suspended. This prevents any environmental damage.
• Fires and smoke formation are effectively prevented and safely extinguished in an emergency. A fire safety certificate confirms compliance with building regulations.
• Explosions are also prevented. The explosion protection concept meets all legal requirements.

The materials and chemicals used or produced by the plant are not classified as “hazardous substances” under the Major Accidents Ordinance (StörfallVO). Following decommissioning of the coal blocks, the plant will continue to be classified as an operating area in the lower class as per the StörfallVO (it was previously classified in the upper class).

The buildings at the plant will be up to 36 meters (m) tall. Its chimney will be 50 meters tall, measured from the power plant’s new level of 180.2 meters above standard zero (“Normalnull” or N.N.).

Thanks to the use of sophisticated technology, the plant does not smell: The air needed to incinerate the sewage sludge (so-called “combustion air”) is extracted from all odorous areas of the plant, creating a vacuum. This vacuum prevents any odorous air from escaping.

The sewage sludge, meanwhile, is delivered via airlocks, for which there is also an extraction system. All of the extracted air is then fed into the incineration process, which destroys all odors. During plant downtimes – when it is being overhauled, for example – the exhaust air is cleaned using filters so that even then no odors can develop.

The operation of the sewage sludge CHP plant will generate emissions. At the same time, the decommissioning of the site’s coal blocks will eliminate all emissions previously generated by the operation of the coal blocks. As a result, fewer airborne pollutants will be released into the environment in the future.

The new plant was put out to tender in anticipation of the latest standards of the 17th Regulation on the Implementation of the Federal Immission Control Act (BImSchV), as amended in 2024, and it exceeds its requirements.

The planned plant also meets all air quality control regulations (TA Luft), precluding any harmful environmental impact and soil changes. This has been confirmed by independent expert surveys in the course of the approval process and is being reviewed by the responsible licensing authority.

Analyses performed by a specialist company have shown that the higher values recorded in a small number of places do not pose a danger to the groundwater. This assessment is based on the results of an accredited laboratory and the maximum permissible pollution levels.

A soil sample at a depth of four to five meters, taken outside the construction site and the coal storage area, detected slightly elevated heavy metal values. These probably come from foundry sands in the backfill materials. They cannot have any impact on the groundwater because a sample taken directly below the first was within normal limits when tested for heavy metal content. Groundwater was not encountered in the course of drilling.

Soil samples from the construction site were also tested. The result shows that the soil mixed with the coal dust contains more carbon, increasing the sample’s TOC (total organic carbon) content and loss on ignition value (proportion of organic and combustible substances). Since these naturally occurring substances are considered harmless, however, the presence of coal dust in the soil does not pose a problem from a toxicological perspective, although it does mean that the soil cannot be reused freely. There is thus no proof that the soil quality has been impaired as a result of coal being stored on the construction site.

The coal residue present as a result of the site’s former use as coal storage facility was removed prior to the actual excavation work and placed in heaps outside the construction site for declaration purposes.

All emissions from the plant are very clearly below the values laid down by air quality control regulations (TA Luft). Accordingly, they have no relevant impact on the wine-growing areas, the agricultural soils and the municipal areas of Walheim and Gemmrigheim. There is therefore no negative impact on humans, animals or the environment.

Most of the sewage sludge delivered to Walheim and recycled at the plant comes from municipal sewage treatment plants in northeastern Baden-Württemberg, where it is a waste product.

The wastewater produced by the exhaust vapor in the course of recycling the sewage sludge is first pretreated and then transported by truck to the sewage treatment plant in Heilbronn. As a further option, EnBW would support the construction of a pipeline for this wastewater.

Sewage sludge is already being transported today, so this is a case of rerouting traffic rather than creating additional traffic. The construction of the plant in Walheim will lead to a considerable reduction in the total mileage because sewage sludge currently has to be transported over very long distances, sometimes up to 500 km, to Lippendorf brown coal power plant near Leipzig.

Much of the sewage sludge that is set to be brought to Walheim in the future is already being transported via the B27. No noticeable increase in the volume of local traffic is therefore expected. Above all, no delivery traffic will pass through the center of Walheim. An average of 60 trucks per day will visit the power plant site to deliver the sewage sludge and take away all operating materials, particularly the wastewater produced by the exhaust vapor. You will find further information in the answer to the question about the route.

EnBW has also commissioned an independent report to examine the potential impact of the project on local transport. It looked at several traffic counts as well as official data. The findings revealed that although additional traffic is created, there is no negative impact on the traffic junctions’ ability to cope. EnBW is also prepared to talk to the municipalities about a sewer force main to Nesselwörth sewage treatment plant in order to reduce truck traffic.

Since an increase in traffic can be stressful for the affected residents, the necessary journeys and routes of the trucks were examined in a traffic report. A comparison of the estimated additional journeys with the current traffic volume has found that the additional volume is in the low single-digit percentage range and is therefore not considered significant. Most vehicles will travel along the A81 and via highways:

Traffic will not pass through Walheim itself, but will instead take the B27 and drive along Mühlstraße directly to the access road leading to the power plant site.

Traffic will also not pass through Gemmrigheim, but will instead travel along the K1625 north of the town and over the Neckar bridge.

In Kirchheim, the majority of the traffic will only travel through the southern industrial area before turning onto the B27 coming from the Neckar bridge via Max-Eyth-Straße. Only a small, unavoidable part of the traffic will use the B27 passing through the town.

The sewage sludge can currently only be delivered by truck because the sewage treatment plants that provide the sewage sludge do not have the necessary infrastructure to transport it by ship or rail. The cost of transferring the sewage sludge to ships or trains elsewhere is very high due to the small delivery radius around the plant in Walheim. EnBW is nonetheless examining the option of transporting it by rail. Alternative methods of transport are also being explored for the removal of the ashes and, if possible, other transport routes will then be used.

As operators of sewage treatment plants where sewage sludge is a waste product, municipalities throughout Germany are responsible for its disposal and are faced with the challenge of having to dispose of between seven and eight million metric tons per year.

Decentralized treatment or incineration of sewage sludge in many small plants is neither economically nor technically feasible. In Baden-Württemberg, there is not yet enough capacity to incinerate sewage sludge, which is why it currently still has to be transported over long distances. The quantities of dewatered sewage sludge and dry sludge agreed with the partner company for sewage sludge ash recycling also correspond to the sludge volume from our catchment area and reflect the actual proportion produced in municipal sewage treatment plants.

The fluidized bed incinerator technology chosen for the new plant is safe, reliable, economical and meets the current legal requirements for controlling air pollution. Compared to older systems, it also features improvements that reduce environmental pollution caused by odors and harmful emissions. These include the ability to take delivery of the sewage sludge in the building with airlocks, activated carbon filters for silo air extraction and treatment of the wastewater produced by the exhaust vapor. Alternative processes such as pyrolysis or hydrothermal carbonization have generally only been tested on a small scale. They require additional energy and are therefore less efficient, not to mention further disadvantages in terms of reliability and the usability of the ashes.

EnBW examined all its sites in northern Baden-Württemberg where planning rights exist for a power plant so that it could recycle the sewage sludge as locally as possible. Walheim proved to be the best location for the new plant:

• Since there is already a power plant on the site, it has an excellent infrastructure.
• The site is conveniently situated, reducing unnecessary journeys to dispose of the sewage sludge.
• Due to the impending coal phaseout, the existing power plant on the site will no longer be needed, freeing it up for a new purpose.
• The new sewage sludge recycling plant is a sensible way of using the existing site without having to develop new land.

There are already well-qualified employees on the site who can operate the new plant.

EnBW concentrated its search on the northeastern part of Baden-Württemberg. There is an as yet unmet need here to recycle regional sewage sludge. Both industrial sites and existing power plants owned by EnBW were considered. The advantage here is that no new areas of land are sealed, existing infrastructure can continue to be used and investment costs are kept as low as possible. With this in mind, Marbach, Obrigheim, Heilbronn and Walheim came under consideration:

• Marbach and Obrigheim were ruled out due to a lack of space and unfavorable conditions relating to planning law as well as the staff composition and infrastructure.
• Heilbronn didn’t have the required planning permission. Furthermore, due to a lack of space, the plant could not be completed in time for the construction of the fuel switch project (which involves replacing coal power plants with modern H2-ready combined cycle gas turbine plants).
• Walheim was therefore chosen as the most suitable location (see question above).

A new building in a different location would require a higher level of investment and involve a more complex approval process – both factors that would have a negative impact on the profitability of the project. The same also goes for sites at existing sewage treatment plants because EnBW does not own any.

Stuttgart Regional Council is the approval authority.

Current calculations assume an investment in the low three-digit million range.

It is expected that around 20 posts will be needed to operate the new plant. Then there are the other posts needed to operate the existing on-site facilities, such as the gas turbine plant.

On behalf of the Federal Network Agency, EnBW was required to operate Walheim coal power plant in the so-called grid reserve until March 31, 2025. Both the Walheim 1 block and the Walheim 2 block have now been officially decommissioned since April 1, 2025.

The new plant will be housed in a building that will be specially constructed on the site of the former coal dump, which has been cleared. Due to the status of the old Block 2, which is set to remain in operation as a grid reserve power plant until the end of March 2025, the use of existing buildings is not possible for regulatory reasons.

The entire power plant site is designated in regional planning policy as a “priority area for regionally significant power plants.” Accordingly, any kind of use that conflicts with this policy is not permitted.

In addition, the gas turbine on the power plant site will continue to operate independently of the decommissioning of the coal blocks, which means that it cannot be used as residential or commercial space.

This is a sewage sludge mono-incineration plant based on fluidized bed technology, a reliable and established method for sewage sludge recycling in Germany. It is in line with the latest technological developments and is used at 23 of 29 existing plants.

The technology is also constantly evolving, which means that the planned plant in Walheim features significant improvements compared to older sewage sludge mono-incineration plants with a stationary fluidized bed. One example of an improvement is the flue gas cleaning system, which effectively reduces pollutants and comfortably meets the stricter emission limits introduced in 2024, in some cases even falling below them.

More modern methods, such as pyrolysis, have not yet been technically perfected and are highly susceptible to failure, which can compromise the safe disposal of sewage sludge. Most of them are still undergoing testing and cannot yet be scaled up.

Since energy is released during sewage sludge incineration, the plant can generate energy in the form of sufficient electricity to meet its own supply needs as well as useful heat. To this end, the plant is technically equipped with a waste heat boiler, a steam turbine and a heat extraction option. The plant generates a surplus of electricity and heat. According to the approval application, it thus meets the definition of a combined heat and power plant pursuant to the 4th and 17th Regulation on the Implementation of the Federal Immission Control Act (BImSchV).

Dewatered sewage sludge, such as that which comes from sewage treatment plants, is still a very moist fuel (approx. 75% water content) and also contains components of substances that cannot be used for energy purposes, such as sand. A large part of the energy generated is therefore used directly in the plant, especially the heat for drying the sewage sludge prior to incineration and the electricity generated to meet the plant’s own needs.

If the delivered sewage sludge meets the necessary criteria, the plant does not require any additional fuel and generates more electricity than it needs itself. This makes the planned concept in Walheim sustainable because other technologies used to recycle sewage sludge are not self-sufficient in energy terms and require fossil fuel.

Some of the heat generated is used internally to increase efficiency, while excess heat could be used externally. The plant therefore has the necessary technical setup for heat extraction, including a connecting pipeline to the property boundary. The plant can extract up to four megawatts thermal (MWth) at full load, which could be used for a local heating supply.

In Walheim, however, there is no local heating network as yet. EnBW is therefore offering support to set up such a network, which can bring further advantages as part of the legally prescribed heat planning at local authority level. EnBW already operates local heating networks nearby, which could potentially be supplied by the plant if no local heating concept can be devised in Walheim.

Municipal sewage sludge mainly comes from the waste that is flushed down the lavatory every day. It is thus a biogenic fuel and the energy generated from it (both electricity and heat) is largely carbon-neutral and therefore “green.”