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How to save vast sums in the sewage sector
RAVENSBURG (sz) – By the beginning of the summer holidays, the civil engineering department of the town of Ravensburg will have invested a total of three million DM in the municipal sewerage system. And the fee-payer, too, will benefit from this investment, for the improved technology will lead to huge cost-savings, as the head of the civil engineering department, Ralph-Michael Jung assured.
Instead of expensive additional storm water tanks which will cause costs between 2,000 and 4,000 DM for each cubic metre of storage volume, cost-favourable “discharge brakes” are currently built into the main sewer to the sewage plant. The simple structure of this new procedure, developed by the engineering company Harald Güthler in Waldshut-Tiengen (D) in cooperation with the Technical University of Konstanz, is persuasive: Instead of receiving sewages in retention tanks before a controlled discharge into the sewage plant is effected, the sewer itself is used for the retention – for example, during heavy rainfall.
Semicircular bows made of steel are targetedly implemented in the sewer with the purpose of retaining most of the sewages in reverse. To guarantee a continued flow of the sewages, a hole applied at the bottom of the “brakes” allows a controlled constant discharge of water. Besides, overflow capacities on top of the brakes will help to avoid negative effects such as backwaters in domestic water connections or upward pressure on manhole covers during an inundation. On the whole, the brakes will reduce “peak discharges” and thus lead to considerably more constant discharges. The sewage plant can cope much better with constant discharges than with shockloads which are quite frequent, for example, during thundershowers.
The new procedure is particularly designed for large, flat sewers as used, for example, in the inflows to the sewage plants, as it allows an effective and economical water protection. Applying the procedure, the town of Ravensburg will gain additional storage capacities of approx. 2,750 cubic metres – an effect that can be realized with just 10 % of the investment cost which would be required for a new storm water tank of appropriate size.
The civil engineering department has combined the measures in the sewers with major reconstruction work in the storm water tank of Mariatal which has previously been the largest tank in the area of Ravensburg with a storage capacity of 3,600 m 3. This volume will be extended to more than 4,700 m 3 in the course of the reconstruction. Besides, the tank will be equipped with modern purification facilities and a state-of-the-art measurement value processing and control.
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