Management of Rain and Waste Water 2005

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 2005, the local sewage plants treated some 640,000 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 Grosser Wannsee lake within a week.

Waste waters are carried in a sewerage network with a total length of 9,360 km with 233,000 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 4,178 km of waste water drains, 1,894 km of combined water drains, 3,166 km of rainwater drains and numerous special structures, such as rainwater overflows, rainwater retention basins and culverts. Waste water collected there is pumped to the sewage plants by 145 pumping stations, through a network of 1,120 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.

Table 1: Capacities, quantities of treated waste water and receiving water bodies of the large sewage plants of Berlin and its suburbs in 2005

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 37 million cu. m. of rainwater per year are drained into water bodies by the separate sewerage system. To clean these quantities, rainwater basins and retention soil filters operate at the main discharge points. Thirty facilities for rainwater treatment had been commissioned as of December 2005.

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 rainwater discharge canals, rainwater overflows, drainage canals, water retention canals and rainwater basins to retain combined sewage during periods of rainfall, and to thus delay its passage to the sewage treatment plant. There are exceptions for situations of heavy rainfall. 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. In 2005, some 3.0 million cu. m. of such combined sewer overflow water reached the water bodies untreated at the approx. 530 rain sewage overflows in operation.The occurrences of such overflow situations and the quantitities discharged fluctuate, as they depend on the frequency of strong rainfall.

Also, most pumping stations are equiped with emergency discharges. In situations of technical malfunction, combined sewage will be discharged into outlet ditches. Of the seventy-four emergency discharges, thirty-five discharge into the Spree river, thirteen into the Havel river, and eighteen into the Teltow Canal. Five discharge into standing surface water bodies, and the remaining three emergency discharges carry water to other pumping stations via waste water drains. Emergency discharge operations also fluctuate heavily between the years. The average annual quantity involved is something like 20,000 cu. m. Retention basins were built in the immediate vicinity of large pumping stations and at the most important sites of the combined sewerage system. These may cope with excess quantities of combined sewage during brief periods of high-intensity rainfalls. Sludge and suspended solid particles are deposited in these retention basins.

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. The waste water management of allotment gardens operates along these same lines.

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

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.

A separate map has been developed to document the drainage situation. It shows the catchment areas of the rainwater drains (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.

To reduce the polluted rainwater loads of water bodies in the area of the separate systems, rainwater purifications plants were built (twenty-one as of 2004), including those on Tegel Lake, the Hohenzollern Canal, the lower Havel river, the Teltow Canal, the Biesdorf dredger lake, and on the Grunewald chain of lakes. Others are in the planning stage or are already being built.