Development and verification of a general approach to describe the efficiency of vortex separators in combined sewer systems.

The water framework directive (CEC, 2000) asks for cost-effective measures for achieving good ecological conditions in receiving waters. Because of low operation costs and good pollutant removal efficiency, vortex separators (VS) are an attractive alternative to traditional stormwater tanks. The German design standard for CSO structures, ATV-A 128 (1992), demands long-term pollution load simulations. Today's simulation software, however, considers the removal processes in CSO structures either very rudimentarily or not at all. The higher pollutant removal efficiency of a structure like a VS cannot be taken into account. This might be one reason why VS are used still comparatively scarcely. A mathematical model describing the removal efficiency could increase the acceptance of VS. Several functions describing the removal efficiency have been derived from model tests or large-scale studies within the last few years. Within this paper, the data from three large-scale studies are used to verify the general applicability of one steady-state and one dynamic approach. The results show that the complex processes involved with CSO facilities and the large error related to monitoring make the validation of models a difficult task. Anyhow, especially the dynamic approach was applicable at all considered facilities.

Modelling of sedimentation and remobilization in in-line storage sewers for stormwater treatment.

A special arrangement of combined sewer overflow tanks is the in-line storage sewer with downstream discharge (ISS-down). This layout has the advantage that, besides the sewer system, no other structures are required for stormwater treatment. The verification of the efficiency with respect to the processes of sedimentation and remobilization of sediment within the in-line storage sewer with downstream discharge is carried out in a combination of a field and a pilot plant study. The model study was carried out using a pilot plant model scaled 1:13. The following is intended to present some results of the pilot plant study and the mathematical empirical modelling of the sedimentation and remobilization process.

A software monitor for intermittent bacteria contamination in urban rivers.

Norwegian receiving waters are of such high water quality that authorities consider opening them for bathing. The leading parameter to monitor the quality of bathing waters is fecal coliform bacteria (FC). For this parameter no rapid detection method is available. The main objective of this case study was to find a way to quickly predict bacteria contamination by observing different online parameters such as flow, conductivity or spectral absorption coefficient (SAC). In this study historical data from 1994 to 2000 was analyzed, and over a period of five weeks water samples were taken and analyzed for bacteria. The analysis of the historical data revealed fundamental sampling problems, which made the data useless for the purpose of this study. The analysis of the data collected for this study showed that exceeding the bathing water standard for bacteria can be predicted by evaluating the SAC with an acceptable accuracy. Furthermore a simple river quality model was implemented, including bacteria as a load fraction. With the help of rain data and discharge predictions expected bacteria numbers exceeding the bathing water standard could also be forecast.

Monitoring in inline storage sewers for stormwater treatment to determine efficiencies.

A special structure of combined sewer overflow tanks is the inline storage sewer with downstream discharge (SKU). This layout has the advantage that besides the sewer system, no other structures are required for storm water treatment. Consequently only very little space is required and compared to combined sewer overflow tanks, there is an enormous potential in reducing costs during construction. To investigate the efficiency of an inline storage sewer, a monitoring station was established in Dortmund-Scharnhorst, Germany. The monitoring station was in operation for a period of 2.5 years. Within this period water samples were taken during a total of 20 discharge events. Besides the complete hydraulic data collection, seven water samplers took more than 5,000 water samples during dry and wet weather. This adds up to a total of more than 20,000 individual lab analyses. The average of the total efficiency for the SKU-West is 86%. 29% of this efficiency can be attributed to the throttle flow. The remaining 57% can be divided into a part of 48% that can be attributed to the process storage and 9% that can be attributed to sedimentation and erosion process.