Membrane unit operations water desalination

In this chapter the possibility of integrating different membrane unit operations in the same industrial cycle or in combination with conventional separation systems is analysed and discussed. Many original solutions in water desalination, agro-food productions and wastewater treatments are reviewed highlighting the advantages achievable in terms of product quality, compactness, rationalization and optimization of productive cycles, reduction of environmental impact and energy saving. 

An industrial reverse osmosis unit consists of many semipermeable membranes packed around highly pressurized saltwater. As desalinated water is pushed out one side, the remaining saltwater, which is now even more concentrated, exits on the other side. A network of reverse osmosis units operating parallel to one another can produce enormous volumes of fresh water from saltwater. 

Some of the largest plants for seawater desalination, wastewater treatment and gas separation are already based on membrane engineering. For example, the Ashkelon Desalination Plant for seawater reverse osmosis (SWRO), in Israel, has been fully operational since December 2005 and produces more than 100 million m3 of desalinated water per year. One of the largest submerged membrane bioreactor unit in the world was recently built in Porto Marghera (Italy) to treat tertiary water. The growth in membrane installations for water treatment in the past decade has resulted in a decreased cost of desalination facilities, with the consequence that the cost of the reclaimed water for membrane plants has also been reduced. 

MD holds great promise as a unit operation for water desalination, by itself and in conjunction with other processes such as RO and traditional distillation. Advances in membrane chemistry and module design are expected to close the gap between these processes in the near future. 

FIGURE 5.4 Principles of operation of two types of membrane water desalination units reverse osmosis and electrodialysis. (From Pryde [22], and reprinted courtesy of Cummings Publishing Co.)... 

Since 2003, RO-based unit operation to remove the radionuclides C Cs, ° Ru, U, Pu) from delay tank is continued, and the performance of the system was found to be promising [49-51]. The final discharge of low-level active waste (i.e., a mixture of evaporator condensate, ADU filtrate, and waste generated from personnel contamination [like hand washing to remove contamination from hand]) is carried out from the delay tank, which temporarily holds low-active waste. We thus evaluated RO for the removal of alpha activity, beta activity, nitrates, and total dissolved salts (TDSs) from delay tank water at the pilot plant. The delay tank water composition is given in Table 26.4. The specification of the membrane module, which was supplied by the Desalination Division of the BARC (Mumbai), is listed in Table 26.5. The module was... 

Seawater desalination is the production of fresh, low-salinity potable or industrial-quality water from a saline water source (sea, bay, or ocean water) via membrane separation or evaporation. Over the past 30 years, desalination technology has made great strides in many arid regions of the world such as the Middle East and the Mediterranean. Today, desalination plants operate in more than 120 countries worldwide, and some desert states, such as Saudi Arabia and the United Arab Emirates, rely on desalinated water for over 70% of their water supply. According to the 2004 desalination plant inventory report prepared by the International Desalination Association (Wagnick Consulting, 2004), by the end of 2003 worldwide there were over 17,000 desalination units with total installed treatment capacity of 37.8 million m /day. Seawater desalination plants contribute approximately 35% (13.2 million m /day) of this capacity. 

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