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INTRODUCTION
The historical water shortages affecting the Tarragona province during the 1970s were significantly overcome in 1989 by the formation of the Tarragona Water Consortium (TWC; http://www.ccaait.com/cat/inici.htm), a public water agency integrated by municipalities and industries, and charged with the construction and operation of a surface water transfer system from the nearby Ebro River. The main initial role of the TWC was to provide the investments necessary for waterproofing the major irrigation channels of the Ebro River irrigation districts (water rights holders); in exchange, the TWC was compensated with a water rights allocation of a maximum flow of 4.0 m3/s and its corresponding maximum annual transfer volume of 120 hm3. The water rights transfer was subject to the condition of using water only for urban and industrial water supplies. By 2000, the TWC had invested 140 million euros, representing a water source development cost of 1.17 €/m3. The urban growth experienced by Tarragona coastal areas since the 1990s has resulted in summer peak water demands that are close to the upper allocation limit of the water transfer system. Considering that the 1989 TWC statutory agreement does not allow for exceeding the upper limit of 4.0 m3/s, the Catalan Water Agency (CWA) initiated a search for alternative options that would balance water supply and water demand in the area, mainly using new or non-conventional water supply sources. A water reclamation demonstration project was conducted from May 2008 to February 2009 to test the feasibility of using municipal secondary effluent as a water source for producing reclaimed water that could be used by the nearby petrochemical park. In 2011, the CWA completed the construction of a large advanced water reclamation plant (AWRP) and a reclaimed water supply network (Molist et al. 2011) that allows secondary urban effluents to become reclaimed water supplies suitable for the nearby petrochemical park (Figure 1).
Caption: Figure 1: Camp de Tarragona AWRP and reclaimed water supply network for industrial facilities at the Tarragona petrochemical park. (1) Tarragona wastewater treatment plant (WWTP); (2) diversion for submarine outfall; (3) Vilaseca-Salou WWTP and Camp de Tarragona AWRP; (4) diversion to north and south sectors of the petrochemical park; (5) reclaimed water storage tank for south sector; and (6) reclaimed water storage tank for north sector.