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72 4. SALINE WATER INTAKES AND PRETREATMENT
ambient seawater salinity and avoid water collection from fresh near-shore aquifers in the vicinity of the plant site.
The Neodren HDD intake technology is patented by the Spanish company Catalana de Perforacions. This technology has been used for over 15 years in over a dozen small- and medium-sized seawater desalination plants in Spain, and currently it is under construction or consideration/pilot testing at a number of other plants worldwide.
The capacity of the collected source seawater depends on: the number and the diameter of the horizontally drilled perforated pipes; the length of the perforated portion of the pipes; and the transmissivity and depth of the seabed in which the collector pipes are drilled.
The natural seabed filtration process removes practically all coarse solids and particulates of a size of 50 mm or larger from the seawater and precludes marine organisms in all phases of development (adults, juveniles, and larvae) from entering the desalination plant (i.e., protects marine life against impingement and entrainment). This system is also an effective barrier against the heavy solid loads generated during algal blooms and oil spills.
Data available to date (Peters et al., 2007), however, indicates that while the HDD system can successfully reduce source seawater turbidity and TOC, this reduction typically is not adequate to directly apply the water collected by the HDD intakes to the SWRO membranes. The source water would need to be pretreated through filtration system prior to RO mem- brane separation.
One of the largest seawater desalination plants in operation at present that uses HDD wells is located in Spaindthe 65,000 m3/day (17 MGD) New Cartagena Canal (San Pedro del Pina- tar) plant. The intake system consists of 20 HDD wells arranged in a fan shapedsee Fig. 4.5.
The individual intake wells are between 500 and 600 m (1600 and 2000 ft) long and have 355 mm (14 in.) diameter. Each well produces between 100 and 140 Lps (2.3 and 3.1 MGD).
FIGURE 4.5 HDD Intake of San Pedro del Pinatar SWRO plant, Spain.