Desalinator, hand-operated

A family uses a commercially available desalinator, similar to those developed by the Navy for life rafts. The essential part of these desalinators is a cellophane-like membrane wrapped around a tube with holes in it. Seawater is forced through the tube by a hand-operated pump at pressures of about 70 atm to produce water with a salt content only 40% higher than that from a typical tap. 

FIGURE 11.11 An emergency hand-operated water desalinator that works by reverse osmosis. It can produce 4.5 L of pure water per hour from seawater. Such devices can be very useful for persons adrift at sea. 

On the other hand, the development of seawater desalination, which was the original target of RO process, was delayed because of the insufficient performance of membrane under operating conditions of high pressure and high salt concentration. 

IMaterials and Scaling Issues. Two aspects of the basically simple desalination process require special attention. One is the high corrosivity of seawater, especially pronounced in the higher temperature distillation processes, which requires the use of corrosion-resistant, and therefore expensive, materials. Typical materials in use are copper—nickel alloys, stainless steel, titanium, and, at lower temperatures, fiber-reinforced polymers and special concrete compositions (39). It is noteworthy that in quest of a lower initial cost, the use of inadequate materials of constmction in many locations combined with poor operation by virtually untrained hands led to rapid deterioration and failure of plants long before their estimated design life. Adequate experience suggests by now how to avoid such failures. The other aspect is scale formation (40,41), discussed in mote detail below. 

Assume that a portable reverse-osmosis apparatus operates on seawater, whose concentrations of constituent ions are listed in Table 18.5, and that the desalinated water output has an effective molarity of about 0.02 M. What minimum pressure must be applied by hand pumping at 297 K to cause reverse... 

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... 

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