A modified Activated Sludge Model to estimate solids production at low and high solids retention

In this paper, a modified version of the IWA-ASM1 model capable of correctly simulating the production of solids over a wide range of solids retention time (SRT) is presented. The parameters of the modified model have been estimated by integrating the results of respirometric and titrimetric tests with those of studies conducted on pilot scale plants that treat industrial wastewaters of differing characteristics. On the basis of the experimental results and their subsequent processing, it appears that the production of solids may be satisfactorily estimated using the modified model in which fractions XP and XI are supposed to be hydrolysable with a first-order kinetic. In the cases that were examined, the constant of the aforementioned kinetics was estimated to be ki=0.012 d-1 and ki=0.014 d-1, for tannery and textile wastewater respectively. A reliable calibration of the parameter ki was possible when data relative to the experiment conducted in the pilot plants for no less than 60 d and in conditions of complete solid retention was utilized.