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Metropolitana Milanese and the environment

Checking against network leaks

Metropolitana Milanese systematically monitors the network for leaks, replacing or repairing damaged pipe sections. Thanks to this activity, the total water loss within the Integrated Water Service is among the lowest in Italy. Together with the academic community, Metropolitana Milanese has implemented research projects seeking for network pressure optimization solutions, one of the main causes of leaks.

Monitoring the underground water table

Metropolitana Milanese keeps constant control of the water table through laboratory testing and level measurement. A number of reasons, industrial consumption in the first place, contributed to the impoverishment of the water table in the past. Nowadays, the industrial water demand in the Milan area has been hugely reduced both because of the closure of some industries with the highest demand for water (Falck, Breda and Pirelli in the northern area of Milan) and because of the industrial water recycling implemented in compliance with the legislation and as a cost-control device. Household consumption can also deplete the water table, particularly in rapidly growing conurbations. From that point of view, there has also been an inverted trend in Milan with a fall of water consumption as many families have moved to the suburban areas.

Controlling the environmental impact

Metropolitana Milanese minimizes the waste production deriving from its activity and, where possible, it reuses the generated waste. The Integrated Water Service produces different waste within each of the three stages in the water cycle:

  1. Waterworks
    The waterworks mainly produces waste related to the water purification. Most of this comes from the activated carbon filters installed in some pumping stations. The activated carbon periodically exhausts its absorption capacity and is first regenerated then disposed of at the end of its lifecycle. In terms of quantity, this is followed by waste from the operation of pumping stations, maintenance and processing work, which includes exhausted lubricant oils, paints, printed circuit boards, ferrous and plastic materials, batteries and reagents. The waste is first decontaminated or made inert so as not to damage the environment and be harmful for humans; then it is collected and disposed of in a controlled manner. Products and components reusable as secondary raw materials (e.g. mineral oils) are collected by external specialized services. Lastly, the remaining materials are disposed of in dedicated landfills.
  2. Sewers
    Waste produced by the sewer service section is mainly sludge deriving from the purging of sewerage pipes during ordinary network maintenance. This sludge is disposed of at wastewater treatment plants.
  3. Wastewater Treatment
    Waste produced by the wastewater treatment process are: sludge, sand, oil, fat and solid material collected from the grilles protecting the plant intakes. The sludge is the result of the digestion by micro-organisms of wastewater organic matter. After the sludge is suitably treated, it can be used in agriculture or as fuel in cement factories. In the near future, wastewater treatment sludge may be used in energy generation. In 2008, the Municipality of Milan appointed the Department of Energy of the Milan Polytechnic to undertake a study evaluating the options for thermal treatment of the sludge.

Metropolitana Milanese is attentive to energy issues. Over 99 percent of its consumption is in the form of of electrical power, with a drop of 7.4 percent between 2006 and 2008. Within the total power consumption, medium voltage systems stand out, in particular pumping systems which use 65 percent of the total with a 6.8 percent reduction over 2007, in line with the reduction of water demand and with the energy-saving procedures introduced by the Company. The result is even better over the 2000-2008 period. The high-voltage power consumption, most of which is used by the Nosedo wastewater treatment plant was reduced by 2.1 percent between 2007 and 2008. A 15.8-percent fall in the low-voltage power consumption is mainly due to the reservoir operations and of the construction sites.

Metropolitana Milanese has introduced the role of energy manager. in 2007.

Promoting the use of recycled water for irrigation

Metropolitana Milanese promotes the use of recycled water in farming, which reduces the drinking water used and the use of the legally non-compliant sewage for irrigation. The Nosedo plant treats all the incoming wastewater for irrigation reuse but only part of it is actually used for that purpose by the Roggia Vettabbia (canal) consortium in a large district to the southeast of the City. The water treated by the San Rocco plant is reuse for irrigation in a large area extending south of Milan and bordering with the province of Pavia.

Monitoring the purification areas

Since 2007, Metropolitana Milanese has monitored the areas where the Nosedo and San Rocco wastewater treatment plants are located to detect their environmental impact and act immediately should contamination occur. This activity is carried out in compliance with instructions by the Italian Ministry for the environment, land and sea. In particular, the monitoring plan defines the quality of surface water, underground water, soil and air. The monitoring has shown the following results:

  • surface water: the presence of the treatment plants has resulted in:
    • p•a reduction in COD, total nitrogen and total phosphorus between 45 and 80 percent and an improvement in the extended biotic index (dropping from class 5 to class 4-3), as well as a toxicity reduction at the San Rocco plant;
    • •an improvement in the chemical, physical and microbiological characteristics of the Roggia Vettabbia canal and of the Cavo Redefossi canal effluents at the Nosedo plant;
  • underground water: the recorded contamination was mainly caused by chlorinated solvents, pesticides and heavy metals not attributable to plant operations. The treatment plants do not interfere with the chemical and physical features of the water table, which is proved by test results that show how the pollutant concentration values measured upstream and downstream of the plants are equal; la tipologia di contaminazione registrata, dovuta principalmente a solventi clorurati, pesticidi e metalli pesanti non imputabile all'esercizio dell'impianto. I depuratori non interferiscono sulle caratteristiche chimico-fisiche della falda e ciò è dimostrato dai risultati delle analisi che mostrano come le concentrazioni di inquinanti misurate a monte e a valle degli impianti non variano;
  • soil: : the low chemical and ecotoxicology levels of the river beds are attributable to the environment with very high anthropization rather than to the treatment plants and to the polluting industries in the past. Before the wastewater treatment plants were built, contaminated sediment was deposited along the watercourse beds and, given the long time required to metabolize deep layers, it will take several years before significant sediment improvements are witnessed;
  • air: no aerosols or malodorous substances have been recorded since the treatment plants are in operation. The emission levels remained below the minimum measuring sensibility of the instruments used to monitor the higher-impact treatment stages and the outlying areas.

Hydraulic civil protection

Metropolitana Milanese protects the urban environment by acting when surface watercourses break their banks. In particular, this type of activity field is related to the Seveso river. After a 35-km (22-mi) above-ground course, the Seveso enters the City and continues underground until it flows into the Naviglio Martesano (a canal), forming the Cavo Redefossi that crosses the City and collects part of the wastewater. In northern Milan, the river has often flooded in the past and this has become more frequent in recent years, since the areas upstream of the Milan urban area have become densely populated. To manage the Seveso, Metropolitana Milanese redefined its procedures in 2003, with the goal of preventing flooding by constantly monitoring the remote level sensor which detects changes in the culvert section of the river during rainfall. Six emergency stages have been defined. When it floods, Metropolitana Milanese uses its own equipment, specialist personnel and workforce to ensure that the Seveso overflow drains into the sewerage system at the fastest possible rate to free the streets of water.

Managing the groundwater

Metropolitana Milanese manages the pumping wells used for irrigation and to lower the level of the water table which has kept rising in recent decades to the point of becoming a hazard for the Metro system and for all the underground works – metro tunnels, underground railway lines, basements and underground levels of public and private buildings. To reduce the level of underground water, Metropolitana Milanese pumps groundwater away and uses it for the City greenery and to feed the old canals used for irrigating farmland south of the City. In some locations (e.g. around the San Paolo hospital and at the Bocconi University), this water is used in heat-pump air-conditioning systems, leading to considerable saved power consumption and air pollution improvement.


Metropolitana Milanese manages the ordinary and extraordinary maintenance of culverts, i.e. the natural and artificial watercourses that run under the city in covered canals. The culvert network extends for 370 km (230 mi) (about 200 km or 124 mi in the city) and runs close beneath the road level, forming a separate system from the sewers that run even deeper. There are still multiple connections between the sewage system and the watercourses that cannot be eliminated, both downstream of the treatment plants, where these connections act as collection points for the recycled water and at several points along the urban course, where the level spillways of the sewage system are located; these are active only during particularly strong rainfalls. For this reason, the two networks are part of a single urban drainage system.