Abstract
Based upon the connection of a simulation program for combined sewer systems with the IAWQ-Activated Sludge Model No.1 the new simulation tool GEMINI was developed, which allows the calculation of sewer and sewage treatment plant as a unit. Some obtained results are presented in an example. They suggest, that for every treatment plant a rate of inflow is determinable, which leads to a minimum of total emissions out of sewer and treatment plant. That optimal value of sewage treatment plant inflow in the example is distinct- ly greater than the design flow rate 2Qs + Qf. (Qs and Qf denote the domestic water flow rate and the infiltration water flow rate, the factor 2 is fixed in German design rules). So it is recognizable, that a rigid connection of sewer and treatment plant not always fulfils the aim of minimization of total emissions.