New Railway Link through the Alps

The AlpTransit Gotthard means a forward-looking flat rail through the Alps. With a planned length of 57 km, the Gotthard Base Tunnel will be the longest railway tunnel in the world - the heart of the new rail link. This pioneer work of the 21st century will lead to a remarkable improvement of the way of travelling and transporting in the middle of Europe.

Together with its ARGE-partners Arnold AG and Aggregat AG (Flüelen), AWATEC AG got the contract for section 106 - waste water treatment Erstfeld. Essentially this contract includes the construction and operation of a treatment plant for waste water from tunnelling with 50 - 150 l/s. LEIBLEIN Lamella Separators are integrated into the treatment plant.

During the building phase of the section Erstfeld, the unpolluted mountain water from the surrounding rock gets into the tunnel. The process water that is necessary for workings inside the tunnel is collected in a drainage trench and is fed to the water treatment plant as combined water. After the transfer by the tunnelling company precleaning is done in a flow-dividing structure which primarily serves as regulation and distribution of the developing water flows and additionally separates gravel, sand and coarse solids. After adding and evenly mixing of a flocculant in the feed, the waste water gets into the LEIBLEIN lamella separators. These constructions perform two tasks at the same time. During the coalescence procedure free and finely distributed, dispersed oils are collected at lamella plate packs and rise up to the surface as drops where a suction skimmer removes them and stores them for disposal. The entered turbid matter that pollutes the ecosystem by colmation is coagulated with the aid of a flocculant, prevented from flowing away by the lamella plate packs and sinks down to the bottom as macro flake (colmation = the backfilling of the streambed and a change in lighting and temperature conditions of the surface water). The so accumulated sludge is discharged by a level controlled pump, dewatered and stored for diposal or further treatment respectively.

Next the accumulating water which has got an elevated pH-value due to concrete works is neutralized by carbon dioxide. This procedure provides advantages compared to the neutralization with mineral acid concerning environmental pollution and job safety: an overacidification or an increase in salinity (eutrophication) of the waste water is excluded; there is also a much easier handling in contrast to the toxic and corrosive mineral acid. Settling of lime precipitating during neutralization is done in the downstream basins.

The starting tube for the tunnel boring machine and the cross-cuts between the main tubes are formed by blast driving. Remains of explosives and the precipitation of the explosion fumes lead to an enrichment of the tunnelling water with nitrogen compounds especially with nitrite and ammonium. They are treated by adding sodium hypochlorite and by filtration with activated carbon. Adsorbable organic halogens (AOX) also bond to the activated carbon when the admissable limit values are exceeded - thus they are filtered out.

In order to make sure of a sufficient reserve capacity a further plant extension is caused from a waste water amount of 50 l/s up, thus a steady flow rate of 150 l/s can be treated. A strong inrush of water can be caught up by two retention basins holding 1,000 m³. Even if the retention volume should not be sufficient a danger to the environment is practically excluded because then an emergency flocculation and neutralization with sulphuric acid apply.

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All in all:

lamella separator - an optimal solution!

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