Transportation of digested sludges over extreme distances

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Courtesy of ALLWEILER GmbH

Sludge is a residual product of sewage treatment that, as a rule, is digested and concentrated. In larger processing plants, it is dehydrated, partially dried and subsequently utilised in other processes. This usually takes the form of incineration and subsequent use as an additive to building materials by the cement industry.

In the sewage treatment plant (STP) of the local authorities association Worbental (Worblaufen, near Berne, Switzerland) the digested sludge is not subjected to any further processing after digestion. Instead, the sludge is pumped to the Berne Regional STP (ARA Region Bern AG) at a distance of 3.85 km and an altitude difference of 17 m. 'This solution was chosen in 1988 as a sludge pipeline was considerably less expensive than the construction of a dehydration and drying plant on our own site. In addition, at that time, sewage sludge could only be used as an agricultural fertilizer in a hygienised form, which would in turn have led to further large scale investments.”, in the words of the Assistant Managing Director, Rolf Lüdi.

As a consequence of the great distance, the pumps had to have the ability to transport large volumes while maintaining a high delivery pressure. The pumps also had to be prepared to cope with untypical hydraulic conditions such as variations in sludge consistency and varying pressures (peaks and lows) in the pipeline.

In 2002, two new Allweiler AG progressing cavity pumps were installed. The pumps from the AE series are amongst the largest of their kind in use in Switzerland. The aggregates were installed in a mutually redundant parallel configuration and guarantee continuous operations even during maintenance and repair. Delivery and assembly was organised by Scheerle AG from Steckborn (TG) as the principle agent of the German manufacturer. Maintenance work is generally carried out by the staff at the STP. R. Lüdi: 'A competent contact in Switzerland was of great importance to us to ensure fast reaction times.'

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