Urban Waste Water

Economical upgrading of existing single-stage trickling filter plants with a supplementary cascaded activated sludge stage

Calculation parameters were worked out for upstream, unvented aeration processes, taking cost-effectiveness into consideration as well. These parameters and economic observations can be used to assist planning and decision-making activities for developing or expanding wastewater treatment plants that use trickling filters or for improving their robustness. The chemical oxygen demand (COD) is the principal parameter for determining the recommended calculations 



When municipal wastewater treatment plants are initially constructed, the aeration process is preferred for advanced, biological effluent treatment. The disadvantage, however, is that large reservoir capacity is needed for low sludge loading and lengthy aerobic retention times. The age of the sludge proved to be the best parameter for measuring the success of wastewater treatment. To ensure proper nitrification along with oxidation of the carbon compounds, the sludge must have reached the proper age. 

The aim of the project was to discover alternative treatment techniques that allow small scale aeration facilities to function with large aerobic sludge masses, thereby lowering investment and operational costs.

This could be implemented with separate and successive carbon and nitrogen oxidation, for which a combination of aeration and packed bed processes could work well. Unvented aeration processes with trickling filters were investigated to determine the performance limits of the process when aerobically aerated sludge masses are not used, either for a certain period of time or not at all. Chemical oxygen demand (COD) served as the principal parameter. 


  • The calculation examples demonstrated that an upstream, unvented aeration process with compact reactors can be used effectively for expanding a one-step wastewater treatment facility with trickling filters and for improving the robustness of a two-step facility. In either case, existing tricking filters must be installed downstream and used for nitrification.
  • These results can also be used to expand small nitrogen-fixing wastewater treatment plants by adding an upstream process for denitrification.

More Project Informations

Project title:  Economical upgrading of existing single-stage trickling filter plants with a supplementary cascaded activated sludge stage

Project number:  02WA9883/6 (TV1) 02WA9884/9 (TV 2)

Project period:  1998 - 2002

Project region:  Germany (Bavaria)

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