Sludge Pre-treatment Processes - Results and Applications

Johannes A. Müller
Institute of Sanitary Engineering and Institute of Mechanical Process Engineering, Post Box 3329,Technical University of Braunschweig, D-38023 Braunschweig, Germany, Email:


Pre-treatment processes are an additional step in the chain of sewage sludge treatment. They have been developed in order to improve subsequent sludge treatment and disposal. Pre-treatment leads to a disintegration of sludge solids, thus changing the sludge structure and solubilizing organic matter. Applied disintegration techniques are mechanical, thermal, chemical and biological.
Pre-treatment processes can be used in various applications. The most important one is the improvement of anaerobic degradation. Disintegration of excess sludge has improved the degree of degradation by 10 to 40% in full-scale investigations. Other applications are the improvement of aerobic stabilisation, the reduction of bulking and foaming, the improvement of conditioning and dewatering properties and the reduction of the number of pathogens.
The selection of pre-treatment method and operational parameters is critical for the process. For the improvement of degradation processes a high degree of disintegration is necessary. Because of the relatively low energy consumption, thermal as well as some mechanical methods perform best. The other methods and devices are more suitable, if a lower degree of disintegration is required. Pre-treatment leads to various side effects. The most important ones are the generation of recalcitrant compounds and odour, which is mainly a problem of thermal and ozone treatment.
Improvement of digestion was evaluated regarding treatment costs, which are in the range of 70 to 150 Euro/MgDS. Economic efficiency was checked for a model plant taking all beneficial as well as negative side effects into account. Break-even could be achieved, if the disposal costs were around 500 Euro/MgDS or higher. This points out that cost efficiency will not be given for every application and has to be carefully assessed.

Key Words

Mass Reduction, Disintegration, Implementation, Economic Efficiency


J. Müller (2002). Sludge Pre-treatment Processes - Results and Applications. World Congress of the International Water Association, Melbourne, Australia, April 2002, Conference Proceedings CD-ROM