1.  THE SUBMARINE OUTFALL: A DESCRIPTION The City of Trapani (Sicily, Italy) is served by a wastewater treatment plant for 115 000 equivalent people, ending with a submarine outfall pipeline for the disposal in the Tyrrhenian Sea (Fig. 1). The whole pipeline is made in HDPE with outer diameter 800 mm; it is 3,1 km long and is allocated in a trench in the sea bottom, 1 to 18 m deep below the surface. The pipe ends with a multi-port diffuser made of two trunks with OD 500 mm. The diffuser trunks form a 120° angle in planar view and are 100 m long (Figure 2). Each trunk is equipped with 15 HDPE circular outlets shaped as nozzles with outer diameter 180 mm. The pipeline is statically stabilised by cast iron rings, concrete anchor blocks and mattresses (Figures 3 and 4).  THE DIGGING TECHNIQUES APPLIED FOR THE TRENCH Nearer half of the trench: traditional bucket digger positioned on a pontoon; farther half of the digging: carried by a special dig-machine moving onto seabed, permitting to follow perfectly the lay-out established. The main disadvantages of the former technique:  pontoon drift due to waves and wind  irregular cross-sections;  larger amounts of dug materials and damage to Posidonia oceanica;  wider cross-section than strictly necessary  less stable pipeline in the seabed  more cast iron rings and anchor blocks required. In the latter technique the special machine operates under remote control from sea surface thanks to a tender boat, which provides hydraulic force and air supplies; it is also assisted by two skilled scuba divers, in order to direct the digging. The engine realizes the trench thanks to milling-machines cutting the sediments of seabed. LCI OF THE PIPELINE: RAW MATERIALS AND ENERGY USED IN FIELD WORKS  LCI OF THE PIPELINE: RAW MATERIALS AND ENERGY USED IN FIELD WORKS Review of the detailed constructive project of the pipeline  identification of the most relevant items involved, both as materials employed and as laying works. Table 1 (below) collects data drawn from the design supply estimate from the point of view of raw materials. Table 2 summarizes the fuel consumptions due both to the traditional digger and to the submarine dig-machine.  ENERGY EMBEDDED IN THE CONSTRUCTION OF THE DISCHARGE PIPE The following step of the work: calculating how much energy is embedded both in materials and in the trench. Each item can be labelled by the amount of its embodied energy, i.e. “the total energy consumed in every process that brings the item to its existing state and given location, such as the processing of raw materials or the transports” (Fava, 1994).  COMMENTING THE RESULTS The larger contribution to embodied energy lies in the pipeline itself, therefore in the polyethylene: 3,1 km length of the 800 mm HDPE pipe correspond actually to more than 300 tons weight. Moreover, EE coefficient for 1 kg of HDPE is significantly greater than for the other materials, whose weights are also lower, except for cast iron. Indexed figures for mass and embedded energy were also calculated and can be found in the full paper (see Proceedings). For instance, the energy embedded in materials + works per 1 Mm3 discharged is (2 704 + 81.53) = 2 785 MJ. The e. e. directly used in the biological treatment of the same WW volume under ordinary conditions is 360 000 MJ. ACKNOWLEDGEMENTS CENTRALTUBI S.p.A., 61026 Lunano (PU, Italy) contributed to this work with some basical data. REFERENCES Fava J.A. (1994). A technical framework for Life Cycle Assessment. SETAC Foundation, United States of America. ASSESSMENT OF THE EMBODIED ENERGY FOR MANUFACTURING AND LAYING A SUBMARINE OUTFALL PIPELINE D. Galbo 1, M. Di Giovanni 2, S. Nicosia 2, P. A. Lanza 2, G. Viviani 2 1 Hydro Engineering s.s, via Rossotti 39, 91011 Alcamo (TP), Italia ; 2 DIIAA, Dipartimento di Ingegneria Idraulica ed Applicazioni Ambientali, Università di Palermo, Viale delle Scienze, 90128 Palermo, Italia (info@hydroeng.it; nicosia@idra.unipa.it) SIDISA.08 SIMPOSIO INTERNAZIONALE DI INGEGNERIA SANITARIA E AMBIENTALE, Firenze, Italia, 24 - 27 Giugno 2008. Table 1 - The materials inventory of the submarine outfall. Table 2 - Fuel consumptions associated with the realization of the trench. Table 3 - Embodied Energy connected with raw materials. Table 4 - Embodied Energy associated with the realization of the trench. Figure 5 - Distribution of Embodied Energy linked to the use of materials (top) and due to the realization of the trench (bottom). UNIVERSITA’ DI PALERMO DIPARTIMENTO DI INGEGNERIA IDRAULICA ED APPLICAZIONI AMBIENTALI Figure 3 - A trunk of HDPE pipeline ready for the launch (a) with cast iron rings in close-up (b). Figure 2 - One of the circular outlets (a) and the diffuser trunks at the bifurcation (b). a) b) Figure 1 - An overview of the submarine outfall pipeline. Figure 4 - A mattress and a cast iron ring fitted onto the pipeline.