With the intent to avoid high investment and operating costs associated with the modernisation of the wastewater treatment plant, it was decided in spring 2010 to opt for a less expensive variant in the form of a wastewater transfer to Nuremberg. The Nuremberg sewer network and the Nuremberg sewage treatment plants operated by the “Stadtentwässerung Nuremberg SUN” can absorb the additional volumes of wastewater from Kalchreuth.
A new pumping station was built for this purpose from October 2012 on the site of the former sewage treatment plant of the municipality of Kalchreuth. The raw water is to be pumped through a pressure pipe approximately 10.5 kilometers long. The line has to overcome a gradient of around 78 m and crosses the 6-lane A3 Nuremberg – Würzburg motorway via an underground pipeline. The pressure line stops at the north-eastern periphery of Nuremberg and the waste water continues in free flow through the existing canals to the Nuremberg sewage treatment plants.
The planning was entrusted to the engineering office ELO-Consult.
The given boundary conditions demanded high pump technology and high expectations. After all, raw untreated sewage had to be pumped at 92 m (302 ft) tdh with a flow rate of 40 l/s (16 gpm).
The engineering office 3S-Consult carried out a water hammer calculation to determine the required torques and control details. The start and stop ramps of the frequency converters were set in accordance with the water hammer calculation specifications, so that the pumps could be optimally adjusted for this topography.
For the selection of the pumps, SUN finally opted for the pump manufacturer Emile Egger, who was able to provide numerous concrete references for this exceptional application with high discharge heads.
Four identical pumps type TA 81-100 H4 LB4B were therefore used. The patented Turo® TA vortex pumps are equipped with a vortex impeller optimised for raw sewage to ensure maximum operational reliability in case of blockages. Due to the high operating pressures, the hydraulic material of the casing and casing cover are made of ductile grey cast iron. Two pumps in series achieve the required height of 92 m. In order to reach the required moment of inertia, a flywheel mass of 565 mm diameter and 186 kg has been installed on each coupling.
The pumps are designed according to the usual Egger standard in a solid process construction. A robust construction, large wall thicknesses and reinforced bearings guarantee a long service life, even under difficult conditions.
Commissioning of the pumps took place in January 2014 in the presence of the pump manufacturer Egger and the training of the operators was carried out by the Egger service team.
Since the commissioning, all four pumps have been working very reliably without any disruptions or clogging.