CSZtimejourney: Renovation of the Darmstadt Central Wastewater Treatment Plant (1994–1996)

A look back:
Almost 30 years ago, the Darmstadt central wastewater treatment plant faced a major challenge: How could the existing old plant cope with increasingly heavy rainfall and rising water protection requirements? The solution was a groundbreaking conversion – now considered a milestone in sustainable water management.

The problem at the time:
Increased wastewater volumes and stricter requirements for treatment capacity necessitated an expansion of the central wastewater treatment plant in Darmstadt. In addition, the sewer network in Darmstadt and the surrounding communities quickly became overloaded during heavy rainfall. The treatment plant was also designed for wastewater treatment, not for the short-term storage and treatment of large amounts of precipitation. Untreated rainwater could allow pollutants such as oils, heavy metals, and suspended solids to enter the receiving water directly.

The solution – conversion of the old plant:
Between 1994 and 1996, the old plant was extensively modernized:

• Rainwater retention basins: Massive reinforced concrete basins with high capacity stored tens of thousands of cubic meters of water.
• Structural solutions: The design took into account loads from water columns, changing fill levels, and chemical effects, with a focus on crack width limitation and durability.
• Filtration and sedimentation systems: Multi-stage processes removed pollutants before water was discharged into the sewage treatment plant or directly into waterways.
• Automation: Control and measurement systems for fill levels, flow, and water quality ensured efficient operation and rapid response to changing weather conditions.
• Construction in existing buildings: Existing structures were integrated and reused in a resource-saving manner.

CSZ as a partner:
CSZ took on the structural engineering (phases 1–6), including:

• Static calculations for large storage volumes
• Detailed planning of durable, dense concrete structures
• Integration of new technology into existing structures
• Support during construction while operations continued

Looking back, the impact is clear:

• Improved purification level of treated water
• Flood protection: Reduced flood risk thanks to large storage capacity
• Water protection: Treated rainwater prevents pollutants from entering the water system
• Sustainability: Repurposing instead of new construction
• Technical durability: Structural solutions ensure robust operation to this day

Conclusion:
The conversion was more than just a technical measure—it was a pioneering feat of engineering. The environment, city, and region continue to benefit from this decision today. CSZ shows how well-thought-out structural design can make a real contribution to environmental and flood protection.