Due to old age the wastewater treatment plant of Hahnstätten required a modernization of several units. It implied the reconstruction of the recirculation system, the sludge recirculation pipe and the stirring units as well as the replacement of an immersed partition wall. Before the modernization the biological treatment of the applied system was separated in an upstream denitrification and a downstream permanent aeration. This operation mode had poor energy efficiency as well as poor purification performance.
The initial control system was based on oxygen and redox potential measurements.

Since the reconstruction of the wastewater treatment plant Hahnstätten, the energy consumption of the plant has been reduced by 36 % and the amount of total nitrogen in the effluent has been reduced by 28 %. Furthermore, the amount of surplus sludge has been reduced by 21 %, the visibility in the clarifier has improved by 36 % and the precipitant has been reduced by 27 %.
The payback of the reconstruction was achieved in less than 3 years solely by energy savings and construction savings.

Method
Efficiency improvement by intermittent nitrification/denitrification

Client
Verbandsgemeindewerke Hahnstätten

Capacity
15,000 PE

Construction time
September 2008