Sewage Sludge

Renewable energy and reduction of emission of greenhouse gas by application of advanced techniques for wastewater and sludge treatment at small and medium size wastewater treatment plants

The use of sludge of wastewater treatment plants (WWTP's) for energy production is depending on the amount of accruing sludge and quality of the sludge. Regarding this, sludge of different WWTP's has been investigated. Furthermore has the method of disintegration been analyses offering a better use of the energetic potential. The conclusion of this work are suggestions on handling sludge and sludge treatment differentiated between the size of WWTP's.

Summary

Procedure and results:

In terms of the Recycling and Disposal Act (KrW-/AbfG) accruing sludge of wastewater treatment plants (WWTP's) has to be minimized. Furthermore should the utilisation of matter and energy be preferred opposite to disposal. In the framework of this project the use of sludge for energy production at small and medium sized WWTP's has been investigated and the reduction of green house gas emission has been evaluated.
For significant process steps within the wastewater and sludge treatment resulting potential of green house gas emission as been estimated. As one option in reducing this emission the anaerobe sludge stabilisation implicating use of bio gas can be applied. In this regard the mesophil and thermophil sludge digestion has been compared and evaluated. Emphasis has been put on the investigation with regard to amount of bio gas produced, degradation of organic matter, strain of process water and dewatering. In general, the stabilisation criteria can be achieved using either of the two operating systems. The advantages of the thermophilic technique are the shorter stand times and the correspondingly smaller reactor volumes required. However, these are offset by the greater level of contamination of the process water, which needs to be taken into account in nitrogen elimination.
Representative results have been derived from measures over a period of two years of a pilot plant using sludge of small and medium sized WWTP's. The investigation considered two-stage systems i.e. mesophil/mesophil as well as thermophil/mesophil operation mode. The results are comparable with the output achieved using anaerobic stabilisation systems, whereby the potential for gas formation is reduced thanks to the greater sludge age of the excess sludge and intermediate storage in a clarigester.
Furthermore has the change from mesophil to thermophil operation mode been investigated for large WWTP's. For the pilot plant estimation for dimensioning have been developed considering significant aspects present at small and medium sized WWTP's. Finally has the anaerobe sludge stabilisation been economically evaluated allowing conclusions for similar systems in practice.

More Project Information

Project title: Renewable energy and reduction of emission of greenhouse gas by application of advanced techniques for wastewater and sludge treatment at small and medium size wastewater treatment plants

Project number: 02WS9966/4

Project period: 1999 - 2002

Project region: Germany (Bavaria)

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