Decentral urban infrastructure system DEUS 21

The small village of Neurott situated in a rural area south of Heidelberg has a population of 60 and is made up of farms and an inn with approximately 30 population equivalents. In the past, domestic wastewater has been collected in septic tanks whose contents had to be disposed of on a regular basis.

The Fraunhofer IGB now has built a modern membrane bioreactor plant (Fig. 1) of approximately 100 population equivalents which was set into operation officially in December 2005. The plant where wastewater and rainwater are separated is intended to showcase the effectiveness and profitability of the DEUS 21 concept. The project is supported by the German Federal Ministry of Education and Research (BMBF).

Figure 2 depicts the concept proposed by the Fraunhofer IGB for the decentralized treatment of domestic wastewater from Neurott. The untreated wastewater is pumped from a mixing and equalizing tank into a preliminary settler. Preliminary sedimentation is only necessary if the preliminary filtration function is temporarily out of order. Preliminary filtration serves to separate the raw wastewater into a solid-free and carbon-poor filtrate that is channeled into the biological purification stage (denitrification and membrane bioreactor) for further treatment and a particle-rich bleed that is collected and transported as primary sludge into the digester of Heidelberg’s central wastewater treatment plant. In the event of a lack of carbon for the biological removal of nitrogen, part of the raw wastewater can be pumped directly from the primary settler into the denitrification reactor.

The biological removal of nitrogen is carried out by the process of pre-denitrification. Here, the pre-clarified wastewater together with the cycling sludge, i. e. returned activated sludge from the MBR, is pumped into a mixed tank where microorganisms convert nitrate to elementary nitrogen. The next treatment stage is nitrification, which takes place in an aerobic bioreactor, followed by membrane filtration to achieve separation of the activated sludge (membrane bioreactor).

The treated effluent is periodically pumped into the Leimbach stream from a collecting well while the secondary sludge is collected in a tank for further treatment at Heidelberg’s central wastewater treatment plant.

Preliminary filtration and the membrane bioreactor both use the rotating disk filter developed at the Fraunhofer IGB. The latter is a dynamic membrane filter with high flux, long operation time before cleaning and low energy consumption. It is composed of a cylindrical housing containing a stack of ceramic membrane disks on a rotating hollow shaft. Through application of a pressure gradient, sludge is filtrated from the outside (influent side) to the inside of the membrane disk, with the result that a covering layer develops on the outside of the membrane. This surface layer is controlled by the centrifugal force field generated.

The rotating disk filter, which is manufactured under license by the company Gebrüder Bellmer is being applied on a large scale for the first time in Heidelberg-Neurott.