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| Fukuoka City, the largest city in Kyushu Main Island, has suffered from | ||
| severe drought because of its geological condition. There are no big | ||
| rivers or lakes near the city,and it is very difficult to construct | ||
| dams for reason of lack of suitable places. | ||
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| Sea Water Desalination Plant | ||
| Especially in 1978, the water supply was restricted in 287 days, and | ||
| only 5 hours water supply in the daytime continued for 71 days. | ||
| Also, in 1994, water supply restricts continued for 295 days, and it | ||
| had a great impact on citizen’s life. | ||
| To cope with this situation, Fukuoka prefecture set up "Fukuoka | ||
| Regional Water Supply Development Plan" in 1997, and organized the | ||
| project of the Sea Water Desalination Plant of which enteprising | ||
| body is Fukuoka District Water Works Agency which comprise of 8 | ||
| cities, 9 towns, and one local public utilities administrative | ||
| agency near Fukuoka City. | ||
| The Agency, which was established in 1973, provides the municipal | ||
| water supply services, serving as a water distributor to municipal | ||
| water supply entities, which provide water to households, and | ||
| commenced the operation of Sea Water Desalination Plant on 2005 of | ||
| which capacity is 50,000 m3 per day. This production amount is about | ||
| 8% of total water demands in Fukuoka metropolitan area. | ||
| There are mainly three methods for seawater desalination, Evaporation | ||
| method, Electro dialysis, Reverse osmosis, and the Agency adopted the | ||
| Reverse osmosis method, which has started to be widely used in the | ||
| country and overseas. | ||
| Reverse osmosis is one of effective seawater desalination method using | ||
| semipermeable membrane process that is permeable to fresh water but not | ||
| to salt. The types of membrane filter used in the plant are UF Membrane, | ||
| High-Pressure RO Membrane, and Low Pressure RO Membrane. | ||
| UF membrane is a spiral wound type porous film and removes not salts but | ||
| suspended matter colloidal materials and viruses from raw seawater by the | ||
| filtration. | ||
 UF Membrane |
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Polyvinylidene Fluoride (PVDF) Spiral Wound Type  |
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| High-pressure RO Membrane, hollow fibers bundle, efficiently removes | |
| dissolved salts from filtered sea water by UF membrane. | |
| High-Pressure RO Menbrane |
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| Cellulose Triacetate Hollow Fiber Type  |
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| High Pressure RO Pump | ||
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Low-pressure RO Membrane is also spiral wound types loose semipermeable |
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| membranes, and it is used for the adjustment of the product water | |
| quality. | |
| Low-pressure RO Membrane |
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Polyamide Spiral Wound Type |
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Using these three type membrane process, the agency produces the fresh |
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| water by removing salts and other impurities from seawater, which has | |
| a salinity of about 3.5% on average. | |
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The other unique system adopted in the plant is Sea Water Intake System |
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| using seawater infiltration intake system. This system can collect quite | |
| clear seawater, which penetrate through the sand on the ocean floor, | |
| without installing grit chamber or other structures, which might affect | |
| the surrounding environment. |
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| Sea Water Intake System | ||
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To collect clear seawater, the water level of an intake tank is lowered |
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| below sea level by onshore intake pumps. The difference in water level | |
| creates a flow causing seawater to flow into the porous intake pipe. | |
| The seawater is drawn up at a very slow rate, less than the critical | |
| velocity of flow, without clogging sand layer. | |
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To produce 50,000m3 fresh water from seawater, about 100,000m3 seawater |
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| is required. After the filtration, the concentrate is discharged to Hakata | |
| Bay. Usually, the salt concentration in seawater is about 3.5%, but | |
| salt concentration of the concentrate is about twice of original | |
| seawater. Then, considering the effect to marine organism, the | |
| concentrate with high salt concentration is diluted by treated municipal | |
| sewage from Wajiro sewage Treatment Plant managed by Fukuoka City, | |
| which is located 4km east from the desalination plant. | |
| Also, the utilization of concentrate, which contains much salt, is | |
| under review. | |
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The membrane process has been widely used in various fields, and the |
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| desalination is one of effective example. In the field of wastewater | |
| treatment, membrane process is also used for Membrane Bioreactor, which | |
| has lots of advantages. | |
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Please refer to http://www.sbmc.or.jp/english/membrane%20bioreactor.htm |
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