Berlin Digital Environmental Atlas 01.10 Sewage Farms

Functioning of Sewage Farms

The sewage farms followed a dewatering concept by J. Hobrecht. In 1869 the Berlin administration made him director of the Berlin Latrine System. Hobrecht divided the city into 12 districts, called radial systems. Each radial system had a pumping station. Pumping stations received domestic, commercial and industrial waste waters as well as precipitation water through gravity flow pipelines. Sewage effluents were conducted from the pumping station through pressure pipelines to sewage farms located outside the city. Some sewage farms were additionally supplied by direct pipelines.

Pressure pipelines discharge waste water at the sewage farms. Waste water is first collected in sedimentation basins made of concrete or earth. Water flows through the tank and most sediments settle to the bottom. Immersion panels hold back floating matter. Sediments settling in the sedimentation basin are regularly evacuated and dewatered at special sludge drying areas. Dewatered sludge was used as a soil conditioner for agriculture and horticulture in early years. The sewage farm trench system is also regularly cleaned, whereby removed sediments are usually deposited directly alongside the trench. After sewage water has passed through the sedimentation basin, e.g. has been mechanically cleaned, it flows through gravity feeders to the terraces.

The natural ground form was not automatically suited for processing sewage waters. Terraces were constructed horizontally or sloping, depending on the surface. They were about 0.25 ha large, and surrounded by embankments. There are three methods of sewage farm treatment. Horizontal terraces are flooded by surrounding distribution ditches. For slope terraces, sewage water overflows the upper bank and irrigates the sloped terrace. Bed terraces with ditch irrigation were also initially used. Waste water flowed through bed terraces in connected parallel furrows, about a meter apart. Only plant roots received water (cf. Fig. 1).

Wild sewage areas are often found near treatment terraces. The overloading of prepared surfaces can be met by directly diverting unpurified water through sluices onto natural land. Sewage water contents are retained during the passage through the soil, adsorbed in topsoil without humus, and handled chemically and biologically. This process supplies agriculturally useful nutrients. Initial yields were high and the majority of fields were used agriculturally and served their own sewage treatment plots. There was a mixed use of grasslands and field cultivation.

Most sewage farms were provided during construction with drainage pipelines at regular intervals for a faster discharge of filtered and purified water, and to provide for aeration and regeneration of soils as well. Drainage water passes through collecting drains and dewatering trenches into the preclarification outlet trenches. Some water from soil passage percolates into ground water.

Fields are flooded in normal operation, and then left until water seeps away and the soil is re-aerated. The next flooding is begun only after re-aeration is completed. These sewage farm rhythms are also oriented to the growth periods of agricultural crops. Four to eight field treatment cycles a year are possible on grasslands, with 2,000-4,000 mm of sewage water. Areas used for cultivation of winter wheat can only be used once a year, with 100-500 mm of waste water.

Sewage farms were overtaxed with increasing amounts of waste water, intensification of agricultural production, and the closure of other sewage farms. This stimulated some sewage farm operators to establish "intensive filter areas". These are permanently flooded and surrounded by high embankments. An inadequate degree of purification is performed here because aerobic processes cannot take place. These areas were not used agriculturally.

Sewage farm structures were often leveled after sewage treatment use was discontinued. Trenches and terraces were filled with material from the embankments, themselves land-fill material.