Modelling in-sewer changes in wastewater quality under aerobic conditions

In the present paper a model for the simulation of in-sewer transformation processes occurring during the transport of wastewater under aerobic condit ions is presented. The basic approach is to use a detailed description of t he transport processes to separate the effect of advection-dispersion in th e variations of concentration (of a certain pollutant in a certain pipe len gth) from those due to transformation processes. The focus is on dry weathe r flow and free surface flows. Processes such as reaeration, heterotrophic growth and decay, hydrolysis, ammonification and biofilm consumption of sub strate and oxygen are considered. Transformation processes are modelled usi ng a similar approach to that of the IAWQ Activated sludge model n degrees 1. Results of tracer experiments are presented showing the relevance of dis persion in pipe flow. The results of sensitivity analysis on the model para meters are presented. The model results are especially sensitive to variati ons in yield and maximum growth rate for heterotrophs. Thus, these paramete rs should be determined experimentally for a given system. Less precise est imates for the other parameters have less impact on the model results. This aspect is especially relevant due to the lack of established methods for t he estimation of these parameters for sewer systems modelling. (C) 1999 Pub lished by Elsevier Science Ltd on behalf of the IAWQ. All rights reserved.