Environmental Engineering Reference
In-Depth Information
States, the more than 60,000 water systems and 15,000 wastewater systems are
among the country's largest energy consumers, using about 75 billion kWh/a na-
tionally. This makes up about 3% of the annual U.S. electricity consumption
(EPRI 1999). To give a further impression of exactly how energy intense the
transport in central water supply systems can be, some selected examples will be
given in the following subsections. Although this will not provide an overall pic-
ture of the energy situation, potentials for improvement possibilities will become
clear.
4.3.1 Lake Constance Water Supply System (BWV)
One example of an energy intense water supply system is the Lake Constance sys-
tem (Bodenseewasserversorgung, BWV) in the South-West of Germany. The long
distance water supply system was constructed back in the 1950s, since the region
was suffering from water shortages due to karst undergrounds. Nowadays, the sys-
tem supplies approximately four million customers in about 180 member commu-
nities (BWV 2006). The primary network consists of around 1,700 km of pipes.
The system source is Lake Constance, from which water is abstracted at a depth of
60 m. To transport the average quantity of 4.2 m³/s to all member communities, as
well as to lift the water, in some cases nearly 400 m, high amounts of energy are
needed. In 2006, 164 GWh/a were consumed by the long distance system (BWV
2006). To compare this with the average annual electricity consumption of a Ger-
man single household - which amounts 2,000 kWh/a (EnergieAgentur.NRW
2006) - a total of 82,000 single households could cover their energy demand with
this amount of energy. The responsibility of the BWV ends at a transfer point at
the communities. To transport the water from there to the customers, the commu-
nities often have to make use of additional energy. For example within the city of
Stuttgart, elevation differences are up to 320 m, making 58 independent pressure
zones and 50 additional pumping stations necessary (Kober 2008).
4.3.2 Mexico City Metropolitan Area Water Supply (MCMA)
The central water supply system of Mexico City Metropolitan Area supplies, at
present, around 66 m³/s to about 16 million customers. The primary network con-
sists of 1,074 km of water pipes and the secondary network of 12,278 km (Torta-
jada 2006). About 68% of the drinking water is abstracted from 'internal sources'
(mainly from the Mexico city aquifer) and 32% from 'external' distant water
sources. From the external sources, 23% is taken from Cutzamala River with a
transport distance of 60-154 km and 9% from the Lerma well field, which is situ-
ated at a distance of 60 km from the metropolitan area with a well depth of 50-300
m. The water from the Cutzamala River has to be pumped to a height of more than
1,000 m, requiring 102 pumping stations to reach the supply area. To realise the
transport of the drinking water from the Lerma well field as well as from the Cut-
zamala River into the city, a pumping power of more than 800 MW was installed.
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