Rottebehaelter with two filter bags or two filter beds system has been increasingly used in rural areas of Germany for the domestic wastewater treatment (figure 28). This system is mostly installed in individual houses for 4 - 40 inhabitants. There are a couple of places where the system is connected to more than 200 inhabitants. However, in Belzig a system with filter bed was installed for several hundred people.

Figure 28: Rottebehaelter with filter bags (Left) and with filter beds (Right)

Most of the Rottebehaelter systems are constructed near residential buildings. The domestic wastewater is discharged into one of the two empty filter bags having a pore size of 1 - 2 mm and made up from non-biodegradable material. The solid materials are retained in the filter bag which is usually filled up in 6 – 8 months. As soon as the filter bag is full, the flow is diverted manually to the next empty filter bag. The filled bag is left for further dewatering and degradation in order to get volume and pathogens reduction as well as a dry material. After 6 - 8 months, the bag with pre-treated materials is taken out through the shutter located on top of the Rottebehaelter and further composted with other household and garden organic waste in a local composter for a year prior to its use in the garden. The filtrate drops down to the bottom of the Rottebehaelter. The collected filtrate is pumped periodically or piped (for a site of good gradient) to the constructed wetland. After treatment in the constructed wetland, it is discharged into the water courses nearby. At some places it is collected in a pond in the garden.

This system has also been implemented in the pilot project in Lambertsmuehle near Cologne city in Germany as a component of resource management sanitation in 2000 (figure 29). The Lambertsmuehle, a historical water mill, has been put under preservation since 1983. It has been reconstructed to a museum. Due to the restoration of the building the wastewater treatment had to be reconstructed as well. The new concept of source control and reuse has been installed for the treatment of wastewater from residents and museum visitors. The flow of nutrients and water in the system is shown in figure 30.

Figure 29: Rottebehaelter with two filter bags in the pilot project Lambertsmuehle

Figure 30: Flow scheme of water and nutrient recycling in the Lambertsmuehle pilot

The wastewater is now separately captured at the source. The source separated flows are treated separately outside of the building. Newly developed sorting toilets where no water is needed for the urine flushing, a mechanical device closing the urine pipe when users stand up and water free urinals have been installed. yellow water is collected and stored in the storage tank until it is used for agricultural purposes. For brown water, a Rottebehaelter system is used. The filtrate, due to urine separation, is nutrient poor, and is mixed with grey water at the bottom of the Rottebehaelter and treated in a constructed wetland. The effluent is discharged into the nearby water course .