Aerobic microbial transformations of pipe and silt trap sediments from combined sewers

A conceptual model for wastewater quality changes during transport in sewers is presented. The model concept includes reaeration and main aerobic and anaerobic microbial processes in water phase and sewer biofilm. Emphasis is on microbial transformations of heterotrophic biomass and soluble and particulate fractions of organic substrate; the inclusion of sulfate respiration in the model concept is outlined. The model concept has been tested in gravity sewers as well as in pressure mains. Oxygen utilization rate measurements of wastewater samples from sewers are used for model calibration. The model is exemplified as a tool for evaluation of wastewater quality changes in an intercepting gravity sewer. The model concept can be used in the design process of sewers taking into account quality aspects. It is recommended to consider sewer processes when addressing functioning of the sewer, wastewater treatment and combined sewer overflow effects. (C) 1998 IAWQ Published by Elsevier Science Ltd. All rights reserved.