Open-ocean intakes

Open ocean intake coagulation and filtration with high-permeability -Boron and chloride... 

The seawater intake facilities are among the key components of every SWRO plant. Adequate and consistent flow and quality of source water over the entire useful life of the plant must be assured. The source water collection system for SWRO desalination plants could be an open-ocean intake or subsurface (beach well) intakes. 

Typically, the open-ocean intake structure is located several hundred to several thousand meters off-shore. The best location of the intake structure in terms of souree water quality is at ocean floor depths of 30 m or higher (deep-water intake). Debris load in the souree water and algal content during red tides at such depths are typically 20 times lower than that in the surface water or the shallow waters of the tidally influenced near-shore area (Gille, 2003). 

Because of the high costs of deep intake stmetures and long pipelines, most of the existing SWRO desalination plants with open-ocean intakes are located in shallow near-shore areas where the ocean floor depth is typically between 3 and 10 m. As a result, plants with open-ocean intakes typically have source water with a high content of debris, solids, and aquatic organisms, which requires elaborate pretreatment prior to SWRO membrane separation. The constmetion material of the intake pipe should be chosen carefully, as possible release of minor constituents may harm the membranes, as the case of phthalates release in the Eilat project (Hasson et ah, 1996). 

For plants with open-ocean intakes, pretreatment facilities are usually more elaborate. In addition to the source water screening equipment, the SWRO plants with open intakes have to be equipped with pretreatment facilities to handle ... 

This issue is very significant for pretreatment systems for seawater desalination plants with open-ocean intakes. Often the source seawater contains small sharp objects (such as shell particles), which can easily puncture the pretreatment membranes and result in a very quick loss of their integrity, unless the damaging particles are removed upstream of the membrane pretreatment system. As discussed previously, to remove sharp seawater particles that can damage the membranes from the source water, the SWRO plant intake system has to incorporate a microscreening system that can remove particles larger than 120 p,m. 

Different concentrations of various metals are observed between open and nearly closed bayg232 effective half-hfe of nOmAg (equation 55) in squids after Chernobyl is 7 (i/2)eff = 130 days, in oysters after the Chernobyl accident r(i/2)eff = 140 days and in oysters after the 26th Chinese test r(i/2)eff = 160 days. The r(i/2)eff value is shorter than the physical half-hfe, Tphys = 249.76 days. Taking T a = 150 days for D9 Ag in oysters, we find that T = 375 days. This number probably reflects the half-residence time of ii° Ag in the sea water rather than the biological half-hfe in the oysters. The 7 (i/2)eff values of ii° Ag for oysters and squids are similar. The specific radioactivity of l° Ag for oysters was found to be 0.026 0.008 Bq/mg silver at the open Japanese coast which compares with value of 0.021 0.005 Bq/mg silver for squid in the Pacific Ocean. This coincidence suggests the similar behaviour of i0 Ag in Pacific Ocean oysters and squids and also a uniform distribuhon of i° Ag in the Pacific Ocean water. Thus the present levels of ii° Ag or lo m g found in the above environmental studies do not ensue a health hazard. The ICRP recommended the value of 2 x 10 Bq for llOmAg us an annual hmit of intake. 

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