Modeling of aerobic wastewater transformations under sewer conditions in the Emscher River, Germany

Abstract

The Emscher River in the Ruhr District, Germany, currently serves as a large wastewater collector receiving untreated, mechanically treated, and biologically treated wastewater. Previous investigations in the river show that bulk water transformations of organic matter under aerobic conditions play a dominant role compared with transformations in the biofilm and sediment. It was found that the activated-sludge concept for modeling bulk water processes under aerobic and anoxic conditions in wastewater treatment plants can be used for the Emscher River when the model is extended to include three hydrolysis processes instead of only one. In 17 experiments covering variations in time and space in the Emscher River, measurements of the oxygen uptake rate (OUR), concentration of easily and slowly biodegradable organic matter, and viable biomass were used to find the stoichiometric and kinetic constants suitable for process modeling. One set of constants was found suitable for model simulations of the river, and a simple model simulation was performed for two reaches of the river. Under aerobic conditions the model simulations showed that approximately 40% of the chemical oxygen demand transformed was easily biodegradable and that the transformation was found to be directly proportional to the concentration of viable biomass when no limitations of easily biodegradable organic matter were present. The modeling concept is general and can be proposed for simulations of wastewater transformations under transport in gravity sewers under aerobic conditions.