The Emscher river in the Ruhr district, Germany, is at present acting as a large wastewater collector receiving untreated and mechanically treated wastewater. Before the Emscher flows into the river Rhine, treatment takes place in a biological wastewater treatment plant. The transformations of the organic matter in the Emscher affect the river catchment, the subsequent treatment and the river quality. This paper focuses on evaluation of methods for quantification of the microbial transformations of wastewater in the Emscher with emphasis on characterization of wastewater quality changes in terms of biodegradability of organic matter and viable biomass. The characterization is based on methods taken from the activated sludge process in wastewater treatment. Methods were evaluated on the basis of laboratory investigations of water samples from the Emscher. Incubation in batch reactors under aerobic, anoxic and anaerobic conditions were made and a case study was performed. The methods described will be used in an intensive study of wastewater transformations in the Emscher river. This study will be a basis for future investigations of wastewater quality changes in the Emscher.
