The drinking water treatment plant in the district of Chiasso in the canton of Tessin in Switzerland not only produces clean water from the Sorgente Rovagina spring, which is located 70m above it, but since November 2009 it has also produced environmentally friendly electrical energy generated by a turbine. This hydropower emanates from the kinetic energy of the water flow derived both from the difference in altitude between the plant and the spring, and pressure equalisation.
In 2007 WABAG Water Technology refurbished and enlarged the San Giorgio drinking water treatment plant in the district of Chiasso. Since then 8,640m³/day of raw water has been conducted to the plant from the Sorgente Rovagina spring along a 1,880m pipeline and then turned into clean drinking water.
The pressure created during this descent is proportional to the geodetic altitude difference between the spring and the filter plant. Moreover, as the pressure is several times that required for plant operation, a pressure reduction valve was previously needed to decrease it. This meant that every hour 50kW of kinetic energy was transformed into sound. As this cannot be used considerable energy potential was lost.
The use of renewable energy is funded in Switzerland
With the introduction, as part of the Power Supply Act from 1 January 2008, of a decree regarding the provision of full cost coverage for the feeding of renewable energy into the grid, the use of such energy potential is being funded by the state. In view of this fact, during the autumn of 2008 the operator of the water treatment plant commissioned WABAG with the planning of a small-scale hydropower plant.
A pump turbine was selected from the three standard types of turbine (Pelton turbine with free outflow, counter-pressure Pelton turbine with closed outflow and reverse running pump turbine) on the basis of the natural and specific, plant-related conditions. This turbine is a modified centrifugal pump which, instead of a motor, is equipped with a generator that converts the kinetic energy of the water flow into electrical energy. The resultant power is fed into the public grid on the spot and paid for in line with the new Power Supply Act.
Using this technology, the drinking water treatment plant has been expanded to include power generation, which not only represents an intelligent contribution to environmental protection, but also reduces plant operating costs.
The turbine at the Chiasso drinking water plant produces 250,000kW of energy yearly, which is sufficient to supply some 50 four-person households. The turbine does not cause any deterioration in water quality as the raw water is both cleaned and treated in the downstream filter system.
Arnold Gmünder, managing director of WABAG Water Technology, is optimistic that in line with the Chiasso model, in the near future numerous water treatment plant operators will start to utilise available energy potential, not just in Switzerland, but also other European countries: “This is because using small-scale power plants, the energy costs relating to water treatment facilities can be reduced, and as the feeding of electricity into the grid is paid for, the ROI on the overall investment can be quickly shortened by an average of three years.”