Das Projekt "Determination of optimum operational parameters to avoid degenerated sludge microbiota in lowload aeration plants" wird vom Umweltbundesamt gefördert und von Papiertechnische Stiftung München durchgeführt. Background situation/Problem area: Approx. 96 percent of all effluents from the papermaking process are biologically treated either directly or indirectly. When existing biological waste water treatment plants are cleaned up or new ones built, they are usually equipped with multi plestages and designed to be rather spacious. The 2ndclarification step normally carries a low to very low load (BOD sludge load BTS smaller than 0,1kg/kgd). Many plant managers are forced to carry out nitrification and denitrification in the 2nd clarifying stage in order to eliminate nitrogen compounds in the light of the ever more stringent legal requirements relating to phosphorus and nitrogen. Although there are only few plant managers who are forced to carry out denitrification at the moment, the trend is clearly on the rise. Such conditions more and more frequently result in operating failures resulting in sludge degeneration leading to poor sludge settling conditions and in serious cases resulting in a violation of the legal requirements in biological waste water treatment plants in particular with multi-stage high-load/lowload plants. The importance of these problems is demonstrated by the most recent results of the PTS-VDP 'Water and Waste' inquiry, in which the most important problems in the biological treatment processes were polled. Many of the works reported malfunctions due to floating or bulking sludge, foam formation and problems in meeting discharging target values. In future, high-load/low-load plants will have to be employed to a greater extent in order to fulfil mandated requirements. The expected problems make it necessary to determine target values for the optimised operation of low-load aeration plants. Research objectives/Research results: The objective of this research project is to improve the clarification performance and ensure the stable operation of the2nd stage of low-load aeration plants. Guidelines and target values should therefore be worked out for the optimised operation of the 2nd clarifying stage of low-load aeration plants, especially for the parameters BTS, tTS, BR and O2, as wellas for the nutrient supply and elimination. Operational studies of 6 waste water treatment plants in recovered paper processing paper mills are to be conducted. Until now 4 anaerobic/aerobic activated sludge plants and 3 PSB/aerobic activated sludge plants have been investigated. Operational data of the treatment plants were evaluated over a period of minimum 3 months and additional investigations of sludge and water samples were executed. Influences of operating parameters such as sludge volume load, sludge volume index, and others on floc morphology and the quantity of filamentous bacteria were detected by the digital processing of microscopic images. All plants report at least occasional problems due to bad settling conditions of the activated sludge. usw.