In sewage treatment plants, wastewater is cleaned of dirt and nutrients in various treatment stages – what remains is known as sewage sludge. It consists of water as well as organic and mineral substances in dissolved and solid form. Sewage sludge contains nutrients and should therefore not be regarded as a waste product, but rather used as a valuable source of energy. With this objective in mind, the central sewage treatment plant in Altenburg was converted and expanded at a cost of around 15 million euros. Thanks to the conversion to modern process technology and the use of CHP units, the plant can now generate electricity and heat from the sewage sludge produced. This not only reduces disposal costs but also makes an important contribution to climate protection.
Technical implementation and innovations
The technical implementation of the project, carried out by PORR's structural engineering team, comprised several steps. First, two new digestion towers were constructed in which the sewage sludge is anaerobically stabilised at temperatures of 35-37°C with the aid of microorganisms and bacteria. This produces digester gas, which is used in the CHP units to generate energy. The two digestion towers, each with a usable volume of 2,100 m³, were welded together from steel plates and offer optimal conditions for the fermentation of sewage sludge.
Another central element of the modernisation was the construction of a new machine house. This houses the pump technology, new centrifuges for more efficient sludge dewatering, as well as three combined heat and power plants. These CHP units use the biogas produced to generate electricity and heat, making the sewage treatment plant largely energy self-sufficient.
Sustainability and environmental protection
By switching to the new process technology and using CHP units, the Altenburg central sewage treatment plant can generate around 2,100 MWh of energy per year. This corresponds to the average annual consumption of around 600 households. At the same time, the avoidance of climate-damaging gases saves around 1,125 tonnes of CO₂ equivalents per year. The plant thus makes an important contribution to climate protection and sustainable regional energy supply.
Challenges and success factors
The modernisation of the Altenburg central wastewater treatment plant presented the PORR project team with numerous challenges. As the existing treatment plant had to remain in operation during the conversion work, precise coordination and planning were required. For example, all wastewater was pumped directly from the sand trap to the aeration tanks via a temporary lift pipe.
The central wastewater treatment plant in Altenburg demonstrates the efficient use of sewage sludge as an energy source. Thanks to advanced processes and combined heat and power plants, it reduces disposal costs and contributes to environmental protection. It serves as an example to other municipalities of how waste can be turned into energy-intensive prospects. In line with ESG criteria, this brings significant energy savings for the sewage treatment plant operator. At the same time, it is in line with PORR's strategy of consistently aligning construction projects with the ‘Green and Lean’ criteria.
