Separation Properties of Biological Sludge

Research project P 14459 Separation Properties of Biological Sludge H. KROISS 26.6.2000 Hypothesis :The efficiency and reliability of activated sludge waste water treatment plants depends to a large extent on the performance of the secondary sedimentation tanks (SSTs). The required separation efficiency for suspended solids has to be >99,5%. This efficiency depends on the ,,crosslinked structure,, of the sludge, where the flocs do not only settle but also aggregate and act as a filter system. The project has two aims: 1) To introduce a new parameter for sludge characterisation in regard to the crosslinked structure , and 2) to measure the strength of the crosslinked structure in order to generate data for an improved modelling of SSTs by CFD calculation. Both aims are linked to improved design of SSTs and better treatment plant operation. Experimental setup: Comprehensive analysis of at least 6 full scale plants over a period of at least 4 weeks, in order to get the required data for the validation of the hypothesis. Sludge structure is the consequence of a complex biol. selection process and of the prevailing living conditions which are still not well understood. The subject of the project is an improved understanding of the relationship between the crosslinked structure of the sludge and the design and operation and efficiency of waste water treatment plants. The device ;,SCHLUMOSED,, (developed by Fuchs) is able to identify the development of a crosslinked structure and to quantify the quality of the structure with respect to its ability for trapping small particles. It measures the settling velocity too! With a simple device, called ;,STRENGTH TESTER,,, the strength of the crosslinked structure shall be measured. The data obtained from it are supposed to play an important role for SST modelling and suspended solids losses to the effluent. This project will be executed jointly by three university institutes: TU Graz: Inst. für Apparate-bau, Mech. Verfahrenstechnik und Feuerungstechnik, Prof. Staudinger (Conotruction and oper-ration of SCHLUMOSED and STRENGTH TESTER, data collection during the whole project); TU Wien: Inst. für Wassergüte und Abfallwirtschaft, Prof. Kroiss (Selection and characterisation of the plants, interpretation of plant operation and characterisation of biocenosis). TU Dresden: Inst. für Siedlungs- und Industriewasserwirtschaft, Prof. Krebs (Modelling of the SST by CFD calculation). It is expected that the project will improve design and operation of activated sludge waste water treatment plants due to better understanding of the processes, new monitoring parameters and improved modelling.