Management of Rain and Waste Water 2012

Introduction

In Berlin, precipitation and waste water from private households, public institutions, industry and trade, as well as run-off from public road areas, generate large quantities of rain and waste water. These need to be piped away and treated, if appropriate. In 2008, the local sewage plants treated some 645,000 cu. m of waste water from private households, trade, industry and public institutions, as well as rainwater from Berlin and its suburban area every day. This quantity is equivalent to a little over 8 cu m/sec., or one third of the Spree river run-off, given medium water flow. The amount of waste water generated in Berlin would be sufficient to fill the Great Wannsee lake within a week.

Waste waters are carried in a sewerage network with a total length of 9500 km with 240,000 service lines. The sewerage network is operated by the Berliner Wasserbetriebe (Berlin Water Works). It was implemented in two different systems, the combined and the separate sewerage systems, and consists of a total of 4300 km of waste water drains, 1900 km of combined water drains, and numerous special drains and special structures, such as rainwater overflows, rainwater retention basins and culverts. Waste water collected there is pumped to the sewage plants by 150 pumping stations, through a network of 1180 km of pressurised sewage pipes.

Berlin’s combined sewage canal system was built In 1873 according to a design by James Hobrecht, to drain Berlin as it was then. However, towns and communities surrounding Berlin, which retained their independence until 1920, mainly built systems based on separate drainage. After their incorporation into Berlin, their facilities were amalgamated into the present system. Drainage areas are oriented towards river courses and shipping canals, and also in accordance with the different terrain heights. The boundaries of drainage areas do not follow the borders of Berlin’s boroughs. Some three quarters of Berlin’s drained areas are operated under the separate system, and the remaining quarter under the combined system.

The Separate System

In a system of separated drainage, waste water and rainwater are handled by two different systems. Waste water drains carry household, commercail and industrial waste water to the pumping stations. From there, pressurised pipes are used to take it to the Ruhleben, Münchehofe, Schönerlinde, Wassmannsdorf, Wansdorf, and Stahnsdorf sewage treatment plants. After treatment, sewage plants discharge purified water into Berlin’s bodies of water. Two other sewage treatment plants – at Marienfelde and Adlershof – were decommissioned as of 1990, and the Falkenberg facility was closed in 2003.

At the pumping stations, there are usually emergency outlets, through which the wastewater can be discharged into the receiving bodies of water in case of technical defects. Of the 74 emergency outlets, 35 lead to the Spree, 18 to the Havel, and 13 to the Teltow Canal; 5 lead to standing surface waters, and 3 to other wastewater pumping stations, via sewage drains. The performance level of the emergency outlets is also very different from year to year. On average, a total of 20,000 cu m/yr. can be assumed.

Table 1: Capacities, quantities of treated waste water and receiving water bodies of the large sewage plants of Berlin and its suburbs in 2011

Rainwater drains collect precipitation from impervious surfaces, cooling water from factories, and water from drainage ditches. This is carried directly to the larger or smaller surface waters. In some cases, very considerable areas of the city drain into very small receiving water bodies. Altogether, some 48 million cu. m. of rainwater per year are drained into water bodies by the separate sewerage system. Rainwater from the separate sewerage systems is heavily polluted by dust, air pollutants, rubbed-off road surface and tire particles, leaked oil, leaves, animal faeces, road grit in winter etc. After more intensive rainfall, there have been repeated fish kills in smaller standing water bodies and canals with relatively little water. This is the result of oxygen-depleting processes resulting from the oxygen-consuming decomposition of drained substances that sets in immediately after the latter reach the water body. To reduce the pollution of water bodies , rainwater basins and retention soil filters for the treatment of rainwater operate at the main discharge points. Twenty-one facilities for rainwater treatment had been commissioned by the Waterworks as of 2012; an additional ten facilities were set up along the motorways.

There are some areas on the boundaries of the inner city which originally operated a combined sewerage system, but later received a rainwater drainage system (a modified combined sewerage system). There, the rainwater is drained into the rain sewage overflow drains of the combined sewerage system.

The Combined System

This system is found within the old inner city of Berlin and also in the area surrounded by the inner circle line of the S-Bahn (urban railway). In this combined drainage system, household, commercial and industrial waste water is collected in a single drain together with the rainwater, and then fed to the next pumping station. From there, the combined sewage water usually takes the same route as the sewage from the separate drainage system. The combined sewerage system includes not only rainwater relief facilities, but also water retention canals and rainwater overflow basins to retain combined sewage during periods of rainfall, and to thus delay its passage to the sewage treatment plant. In 2012, 17 such plants were in operation. In brief heavy rainfall, they are able to completely take up the mixed water overflow. There are exceptions for situations of extended, intensive rainfall events. Once water reaches a certain height in the drains, or if the pumping stations can no longer cope with volume of water received, the combined sewage – which, in case of such downpours, consists mainly of rainwater (at a ratio of about 1:9) – flows untreated into the water bodies via rainwater overflow canals. The occurrences of such overflow situations and the quantitities discharged from the combined system into the receiving waters fluctuate, depending on the frequency of strong rainfall. The central overflows near the pumping station, including the overflows of the rainwater retention basins, were measured and recorded. Thus, in 2011, approx. the 4.5 million cu m of mixed water which entered the waters accounted for some 65% of the total amount of overflow water entering those bodies of water. The mixed water overflows remote from pumping station were not measured and recorded.

Areas with no Connection to the Sewerage Network

Despite considerable efforts by the Berlin Water Works (BWB), not all inhabited areas have been connected to the sewerage network as yet. In those built-up areas of Berlin with no house connections, sewage is collected in septic tanks with no discharge, from where it is taken to sewage treatment plants by authorised transport companies.

In areas without rainwater drains, rainwater seeps into the ground.

A separate map has been developed to document the drainage situation. It shows the catchment areas of the rainwater drains (Map 02.09.2). Every built-up area connected to the storm-water drainage system is matched to the water body receiving these discharged quantities of rainwater.