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February 2001

Tunnel Vision

The evolution of Munichs first-rate sewerage treatment system

Under the surface of every living city lies a complex network of intertwining cables, pipes and tunnels that carry the city’s life force. Power pulses, information flies, gas and water flow and subways carry inhabitants to their chosen destinations. And underneath it all lie the sewers, extensive waste disposal networks that flush out waste and help keep the city salubrious.

Munich, like other major European cities, has a complex system of pipelines, treatment systems and pumping stations to handle its wastewaters. But what makes Munich truly notable is the modernization program undertaken in the last two decades that has resulted in one of the most environmentally friendly sewerage treatment systems in Europe. At the heart of this 2,300-km-long canal network is the Klärwerk Gut Marienhof, a vast treatment complex completed in 1989 at the cost of DM 567 million. The single most expensive construction project ever undertaken by the City of Munich, Gut Marienhof can handle up to 5,000 liters of water a second and release them, sifted and purified, into the Isar — helping to make it one of the cleanest rivers running through any large European city today.

Water is the basis of life and its importance cannot be overestimated. All people depend on it for drinking, cooking, washing and carrying away waste, as well as for other domestic and industrial activities. The challenge of urban communities has always been to ensure its ready availability. The supply of water is, however, not the only challenge. A critical concern is water quality — and this is linked to water treatment and disposal. Janus like, water, the bringer of life, can also be the bearer of death, and even the ancients knew the importance of water purity. Sanskrit writings from as early as 2000 BC tell how to purify water by boiling and filtering it, while sanitary sewers have even been found in the ruins of prehistoric Crete and Assyrian cities.

The first recorded attempt of the City of Munich to provide potable water to its citizens was in 1422, when it financed the construction of a fountain. It was not until the modern era, however, that any serious effort was made to come to grips with the problem of waste disposal.

For much of its history, Munich was a particularly unsanitary place. Waste was dumped directly in the streets or into cesspools. When these became full, the waste was removed at the owner’s expense, and used as fertilizer on surrounding fields or dumped directly into the Isar, which was expected to carry it beyond the sight and olfactory range of Munich’s inhabitants.

This solution was unsatisfactory — particularly for those living downstream in Landshut. Not surprisingly, Munich itself was also continually wracked by epidemics that devastated the population and weakened the economy. Although the exact link between polluted water and the epidemics eluded the city elders, they must have had suspicions. The continual growth in popularity of beer as a drink in Munich can in part be traced back to the population’s doubts about the quality of their water.

It was not until the 19th century, when a direct link between water quality and cholera was established, that the wheels were set in motion to devise comprehensive sanitation systems in European cities. The first closed sewerage canal in Munich was constructed from Promenadeplatz to Hofgraben in 1811. In the following years, more than 20 km of sewerage canals were built. These were not, however, built to a central plan, but laid out haphazardly and were insufficient to deal with the rapidly expanding population — and waste continued to flow freely into the Isar.

Munich was again struck by severe epidemics in 1836 and 1854. The latter disrupted an international industrial exhibition at the Glaspalast (Glass Palace). Thousands of international visitors fled in panic as the epidemic claimed 2,936 lives — including that of Therese, the wife of King Ludwig I.

The Upper Bavarian government responded to the catastrophe by demanding that Munich clean up its act. A comprehensive pipe system was subsequently created to carry rain and cookingwaste water, but human waste still needed to be carted off. To avoid cartage costs, Munich citizens began sneaking out at night and dumping the contents of their bed pans and cesspits into the sewerage system. The inadequacies of this system were exposed in 1873 when yet another cholera epidemic swept the city, killing 1,500 people. The British engineer J. Gordon, who was in the process of completing a sewerage system for Frankfurt, was quickly commissioned to create a comprehensive plan for all of Munich’s wastewaters — a closed system that would be able to handle all wastes and efficiently flush them away.

At the same time, Max von Pettenkofer, a local chemist and pharmacist and a continual agitator for efficient waste disposal methods, was actively campaigning for the introduction of the English water closet (already used in England since 1810 and not invented, as legend has it, by Thomas Crapper). Pettenkofer also promoted the use of special resistant cement and clinker bricks for the construction of sewers and insisted that any plan should allow for the expansion of the city population far beyond its then 130,000 residents. His proposals were incorporated into Gordon’s plans, and many of Pettenkofer’s sewers remain unchanged to this day — even after carrying more than a century’s worth of human waste.

Pettenkofer’s legacy is also found in the quality of Munich’s water. He insisted that the Mangfall River be used as the source of the city’s freshwater supply and, as a result, Munich residents still drink some of the highest-quality water in the world.

Construction on the first section of the Gordon plan began in 1881 and, by 1900, 225 km of sewerage canals were complete. In 1926, the much-abused Isar finally received a break when the Klärwerk Grosslappen, near Ismaning, was built. The new facility used mechanical sedimentation tanks and large fish lagoons to clean wastewater biologically before discharging it into the river. According to an official at the Stadtentwässerungswerke München, the fish serve solely as a natural monitor of water quality. Like canaries in a coal mine, they go belly up if there is a serious problem with the surrounding environment. Although the Klärwerk Grosslappen has been continually upgraded, by the 1980s, the complex handled more than 220 million cubic meters of wastewater annually. It was clearly overloaded.

Meanwhile, growing environmental awareness meant health concerns had advanced from simply concentrating on the chronic effects of water quality to focusing on chemical and industrial contamination. More stringent methods were needed to remove the increasingly complex cocktail of organic and inorganic chemicals (such as ammonium poisons), turbidity and microorganisms polluting today’s water.

The solution was the creation of a second Klärwerk. Proposals for such a facility had been made as far back as 1938, but it was not until 1984 that construction actually began. The new facility, which would lie north of Munich, near Dietersheim, would be state of the art and apply the most modern cleansing procedures to wastewater.

The result is Klärwerk Gut Marienhof, a massive sewerage treatment plant that went into operation in 1989 — and provided the local press with a continual string of articles about backhanders, tax evasion and bribes. Designed to blend into the sensitive environment of the Isar greenbelt (the facility has won three architectural prizes), Gut Marienhof alleviates Grosslappen of 40 percent of its previous volume. In addition, it processes the large volume of waste from Allach, Feldmoching and other outlying areas delivered via the 30-km-long Nordwest Sammelkanal (an impressive engineering feat costing DM 520 million).

Wastewater enters Gut Marienhof at an average of 2,500 liters a second in dry weather (5,000 liters a second when it rains). This is the equivalent of approximately one fifth of the entire water volume of the Isar pouring through the plant each year.

In all, it takes 19 hours for the water to proceed through the facility. The primary stage involves mechanical cleansing and begins with a coarse raking that catches large insoluble materials. This refuse is removed from the water and later shipped to the Kraftwerk Nord where it goes into a furnace that produces some of central Munich’s wintertime heating. Spiral-flow aerated grit chambers are then used to remove sand, silt, gravel and cinders, as well as fats and oils. With the grit removed, the water then sits in sedimentation tanks for 2 1/2 hours. This allows organic matter to settle and to be drawn out for disposal. This process removes up to 35 percent of all pollutants.

The wastewater is then siphoned off for second-stage cleansing, which includes a complex two-step biological procedure known as digestion. During digestion, the wastewater is subject to a process that converts sludge to methane, carbon dioxide and an inoffensive humus-like material. These reactions occur by using enzymes and bacteria in closed tanks. By the time the microbial process is complete, the wastewater has been thoroughly cleansed. To catch remaining pollutants and organic matter (an indirect result of the biological process), the water is fed through a sand filter.

Notable steps in the Gut Marienhof procedure include a special denitrification process borrowed from the United States. Rank air is extracted from the Rake House and other locations, enriched with methanol and fed into the biological vats to help the existing microorganisms break down the nitrates in the water. Methane gas is also extracted and used to power half of the facility’s machinery. All remaining solid wastes are later pumped through a 12-km-long pipe to Grosslappen for incineration.

More than 940 people are employed to plan, build, maintain and monitor Munich’s entire sewerage system. And those 225 km of sewers completed by 1900 have now been expanded to 2,300 km of underground tunnels and pipes, 33,400 shafts, 64,000 street drains and 102 pumping stations — and the system continues to grow. Construction is now beginning on large new canals for the Mittlerer Ring Ost and Mittlerer Ring Südwest. The Nordwest-Sammelkanal was recently extended by 2 km. The extension of the tunnel was completed in January at the cost of DM 44 million.

Tours of the subterranean side of Munich can be organized and sewerage workers — equipped with gas detectors and special lamps — lead tour groups through the flickering shadows and echoing tunnels of this nocturnal world. It is a world of bizarre acoustics, sudden water surges, pungent odors and the distant muffled sounds of city life overhead. Some canals are made of clinker bricks, others of concrete. Some canals are narrow and full of tight nooks, while others are as wide as U-Bahn tunnels. Somewhat apprehensive visitors strive to stay as close to the light-wielding guide as possible. Though tour veterans agree that the stench of the facility’s rake house leaves a bit to be desired — one participant was overheard speculating as to whether he might discard his sewer-scented clothing upon returning home — most feel that a walk through this underground network is a fascinating one.

Film studios occasionally request the use of a huge storm-water tank at Schenkendorfstrasse for banquets. Groups of youth have been known to stage impromptu parties in the tunnels (a practice, which is both illegal and dangerous).

It is also possible to tour Gut Marienhof and marvel at the sophisticated and complex technology used to solve such a basic human problem. The ingenuity of the entire process and the sheer size of the complex is staggering — and well worth seeing. Each person within this city produces an average of 281 liters of dirty water per day (including water used in commerce and industry). This, plus run-off produced from rain, is processed daily and then fed back into the hydrology process.

At the end of the process, the water from Marienhof is 99 percent cleansed, while that from Grosslappen has more than 97 percent of all pollutants removed. This figure will further improve when the upgrading of facilities at Grosslappen is completed. This water, fed indirectly into the Isar, is of a high quality and suitable for fishing and swimming, but — like much unprocessed, natural water — not for drinking.

Despite the extensive infrastructure involved, however, the cost of potable water in Munich is less than DM 2 per cubic meter, whereas the cost of cleansing one cubic meter of wastewater comes in at around DM 1. In return, we enjoy one of the leading environmentally-friendly works and one that has substantially contributed to cleaning up the Isar.

An examination of the Bavarian water charts reveals that dramatic alterations in water quality have occurred in the past 30 years. In the late 1960s, much of the rivers and creeks were highly or excessively polluted — some to the point of being sterile and devoid of aquatic life. By 1993, this picture had changed and improvements had been experienced in most rivers, lakes and creeks. The Isar, too, has been rehabilitated. Previously it was considered to contain far too many pollutants — particularly near Munich. But the condition of the river has improved significantly since then, and this largely due to the opening of Gut Marienhof. There are still concerns. The Werkkanal near the Oberföhringer Wehr, for example, is rated at class III (highly polluted), but the aim is to improve its rating to class II.

Yet, even if the river is rehabilitated, the question is what will happen in the long term? Steady population growth, urbanization and industrial developments will mean that increasing demands will be placed on the infrastructure of the city. Careful planning, design and construction of water supply and water treatment facilities will be required to meet these demands and it may be necessary to question if the current sewerage disposal system is the most optimum — if this incredible use of water, the stuff of life, is really the most practical way to handle the problem.

As Sim Van Der Ryn noted in his 1978 book, The Toilet Papers, “Our excreta — not wastes, but misplaced resources — end up destroying food chains, food supply and water quality in rivers and oceans. How did it come to pass that we devised such an enormously wasteful and expensive system to solve a simple problem?”

Tours of Klärwerk Gut Marienhof and of the Munich sewers can be arranged by calling (089) 233 620 09. The tour of Gut Marienhof provides an in-depth insight into the complex functions of this facility. Those suffering from claustrophobia should avoid the tanks.

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