For over two years, special investigations and practical experiences were evaluated at small wastewater treatment plants with SBR-technology in rural areas in Bavaria. The plants are designed for advanced wastewater treatment with extended aeration. Plants of this type are suitable for small treatment plants, which have to cope with stringent treatment requirements and little available land. The machinery and controlling equipment are constructed with highly sophisticated technology. The constant cycles with time fixed process phases have been proved to be sufficient, but the phases should be optimized and adapted individually to an empirically analysed load line for each plant. The composition of the biocenosis was stable and efficient. The amount of filamentous bacteria was not high. The biocenosis of the ciliated protozoa was dominated by free-swimming species. Plants with two reactors and cycle durations of 10 hours should have a buffer tank in front of the reactors in order to equalize the loading of each reactor. A polishing pond should always be built before discharge into the receiving body of water. The investment costs are comparatively low, but the current energy consumption is higher than in activated treatment plants with continuous operation. Although the automatically controlled process requires little continuous assistance, skilled operators are needed for operation, maintenance and manual control.

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