Central sewage treatment plant, Altenburg

Sewage sludge disposal is expensive and generates high levels of CO₂ emissions. This is why more and more municipalities are investing in modern drainage technology and opting for combined heat and power (CHP) plants to use the waste from the sewage treatment plants as fuel for generating electricity and heat.

Following a restructuring of its processes, the Central Sewage Treatment Plant Altenburg (Zentrale Kläranlage Altenburg, ZKA) is also using this climate-friendly method of generating electricity as its main source of energy. Around 2,100 MWh of energy can be generated annually in the three digester gas-powered CHP units. This technical modification eliminates around 1,125t of greenhouse gases per year.

PORR provides extensive engineering expertise
The Berlin branch of PORR Civil Engineering was the general contractor responsible for the conversion and expansion of the plant. The contract comprised specialist civil engineering services for the foundation of new tanks and buildings, earthworks and landscaping, concrete construction, fit-out, and mechanical installations for the new sections of the plant, including the commissioning of the new process technology. The technical processing within the framework of the plant design is being carried out by pde Integrale Planung GmbH.

A coarse screening building with a screw pumping station, a primary clarifier, two digestion towers, a gas treatment plant including a 12m high sewage gas storage tank with a diameter of 18m, a height of 12m and a filling volume of 2,400m³, and a powerhouse were added to the existing sewage treatment plant.

It was built from reinforced concrete and houses the pump systems, new centrifuges for more efficient sludge dewatering and three CHP units.

The two 17m high digestion towers, each with a diameter of 14m and a useful volume of 2,100m³, are made of steel plates which were welded together on the construction site. Their purpose is to digest and stabilise the sewage sludge, making it easier to dewater and utilise afterwards. The digester gas produced during fermentation is used to generate electricity and heat in the CHP units, effectively making the sewage treatment plant self-sufficient in terms of energy.

High degree of coordination required
The confined construction area means that a great deal of coordination is required. As the sewage treatment plant was kept running while the conversion work was being carried out, all the wastewater was pumped directly from the grit chamber into the aeration basins via a temporary siphon line while the primary clarifier was being constructed. The civil engineering team mastered the construction task with all the associated challenges with flying colours.