Sewage Sludge Treatment

Cost and energy savings associated with the application of high-performance digestion

The incorporation of a high-capacity stage, based upon the principle of the Schwarting-Uhde process, into an existing sludge digestion installation has resulted in stable operation, associated with higher biogas production, improved degradation rates and reduced operating costs. Results obtained are effectively transferable to other sewage treatment plants handling different sewage sludges.


The local sewage treatment authority of Heidelberg had previously operated a sludge digestion facility which, for some years, had been affected by high levels of foam formation and the overflow of foam from the digestion tower.  The operational malfunctions associated with these occurrences generated substantial costs.

In conjunction with this project, and in order to improve this situation, it was decided to incorporate a high-capacity digestion process using the Schwarting-Uhde principle as the initial stage of conventional sludge digestion, using state-of-the-art technology.  The procedure applied involves a two-stage process, comprising a generally mesophilic first stage (37°C) and a second thermophilic stage (55°C).


  • Following the construction and integration of the high-capacity digestion facility into the overall installation, advanced sludge digestion was initiated with peak load and light load stages using the “Heidelberg process”.  By increasing throughput in stages, it has been possible to reduce the initial dwell time of fifteen days to five days.
  • This process is characterised by a high level of biogas production, high degradation rates for dry organic matter and low operating costs.  Savings of 32% have been recorded for flocculants alone.  In addition, cost reductions of the order of 20% have been achieved for the disposal of dewatered sludge.
  • Results obtained using the high-capacity Heidelberg sludge digestion process can be very effectively transferred to other sewage treatment facilities.

Project Participants

Implementing Institutions

Abwasserzweckverband Heidelberg

More Project Information

Project title: Cost and energy savings associated with the application of high-performance digestion, with demonstrable transferability to other municipalities and sewage treatment plants

Project number: 02WI0037

Project period: 2000 - 2002

Project region: Germany (Baden-Württemberg)

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Source: German National Library of Science and Technology Hannover (TIB)