The lagoon of Venice is the largest in Italy and is situated between the drainage basin of the mainland and the sea. It has been subjected to more and more pollution due to increasing industrial and agricultural developments in the region.

In 2000, the Regional Government of Veneto set up a master plan to prevent further pollution and treat the water running from the basin into the lagoon. The project Fusina forms the main part of the planned efforts and ranks regarding its extent and integral approach concerning wastewater treatment and environmental protection among the first in Europe.

Within the bounds of this project, the existing treatment plant in Fusina is transformed into a ‘multipurpose facility’ that purifies sanitary sewage and stormwater of Mestre, Marghera and Mirese–which together has approximately 350,000 inhabitants, industrial effluents and polluted groundwater from the Marghera harbor.

In order to optimise the treatment, the new plant collects sewage separately and according to the following scheme:

• Sewage type A: Sanitary sewage and stormwater from Mestre, Marghera and 17 towns in the region Mirese
• Sewage type B1: Industrial effluents from the Marghera port basin
• Sewage type B2: Stormwater and sullage
• Sewage type B3: Polluted groundwater.

Type A sewage is biologically treated with ultrafiltration membranes and consequently phytodepuration. The latter is conducted on an area of around 15 hectares where the water is purified through metabolic processes of nymphae (water lilies) and other water plants. Walks and bikeways were built between the naturalistic water lanes to make the area attractive also for recreation. Instead of daily diverting 75 m³ of water from the river Sile, the treated water is used by local industries and for cooling water in petrochemical plants.

Purified type B sewage and exceeding type A water, that cannot be re-used, is led through a 20 km long DN 1,400 pipeline into the sea.

The total costs for the planning and realisation of the master plan amounts to €194 million, of which €93 million is financed by the Regional Government Veneto. The rest is provided for by the grantee Sistema Integrato Fusina Ambiente – Integral Environmental System Fusina (S.I.F.A.) whose major shareholders are Veneto Acque SpA, Veritas SpA and Impresa Mantovani SpA.

The 20 km long outlet to the sea conveys the treated water 10 km from the plant in Fusina to Lido di Venezia, and another 10 km to the sea where large tanker ships dock. In order to cross the Lido sandbar, 351 m DN 1,400, PN six pipes were installed by microtunnelling. The general contractor Impresa Costruzioni Mantovani was responsible for the installation and entrusted I.CO.P. SpA with the microtunnelling job.

Site Manager at Mantovani SpA and engineer Meneghini said “It took a long time for us to find a pipe that suits our requirements.

“We needed a jacking pipe that would also withstand the operating pressure of the line. After a long research period we chose HOBAS CC-GRP Jacking Pipes since these inherently possess the characteristics necessary for jacking as well as for pressure pipes: mechanical strength and optimal hydraulic properties. Normally, two different pipe systems would have been utilised to match all requirements.”

The HOBAS CC-GRP Jacking Pressure Pipes that were chosen in 3 m sections, with an external diameter of 1,720 mm and a wall thickness of 85 mm allow a maximal jacking force of 6,926 kN.

The leak-tight pipe system with its high performance couplings is produced to withstand an operating pressure of 6 to 10 bar. The very smooth outer surface of the pipes enabled comparably low jacking forces and allowed a single jack over the complete section of 351 m. Only the starting and receiving pit were used saving on three originally planned intermediate stations.

Thanks to the use of a microtunnel boring machine drill head with a hydraulic soil removal system and the smooth surface of HOBAS CC-GRP Pipes the line was installed within less than a month. The extremely small roughness co-efficient of the inner liner of the pipes and the, comparatively light wall construction reduced the volume of excavated material considerably keeping costs to a minimum and making the installation a complete success.