Membrane and Desalination Technologies - TCE Moodle Website

Desalination of Seawater by Reverse Osmosis 595
Table 13.6
Water production cost (1996) (65)
Items Cost (USD/1,000 gal)
Sulfuric acid (130 ppm) 0.03
Scale inhibitor (3 ppm [Flocon-100]) 0.03
Chlorine (10 ppm) 0.01
Sodium hydroxide (40 ppm) 0.03
Electricity power 0.34
Labor cost 0.19
Miscellaneous 0.1
Total 0.73
6. RECENT ADVANCES IN RO TECHNOLOGY FOR SEAWATER
DESALINATION
Desalination is becoming popular because of the decrease in reliable water sources and
increase in the global population. The total desalination capacity of the world is estimated to be
40 million m 3 /day (70), whereas the seawater desalination accounts for 24.5 million m 3 /day
(71). As discussed earlier, RO technology is one of the widely using seawater desalination
technologies. In order to meet the demand, RO technology has to be improved in many
aspects, and deficiencies in the technology must be minimized. Recent developments in the
field of RO desalination of seawater to avoid the deficiencies are discussed in this section.
About 70% of the operating cost of seawater RO desalination is the energy cost (72). On
the contrary, energy is as important as water and is becoming scarce. Therefore, energy
recovery devices and alternative energy sources receive the attention of the scientific community.
Energy recovery devices discussed earlier in this chapter are modified further in
recent studies. A novel “fluid switcher” is introduced to the energy recovery devices. It is said
that the hydraulic recovery efficiency is increased to 76.83% after the introduction of the
“fluid switcher” (73). Alternative renewable energy sources are evaluated for the seawater
RO desalination, especially for the small communities in rural areas where electricity is not
available. A plant with capacity of 20 m 3 /day was evaluated for the possibilities of using
photovoltaic (PV) array as the energy source. Modeling study showed that the solar-driven
plant is a favorable energy option compared to a fully diesel-driven or diesel-assisted PV-RO
plant (74). In another study, solar organic rankine cycle engines are proposed for a plant with
a capacity of 15 m 3 /day (75). Wave energy is another option proposed for small-scale
seawater RO desalination plants. RO plant with a pressure exchanger intensifier and with
specific energy consumption less than 2 kWh/m 3 was recognized as the promising location
where the wave energy can be utilized (76). Possibility of use of the energy from fuel cells
(77), PV energy (78), and hydrostatic pressure (79) was evaluated as well.
Attention has been paid to improving the recovery of the RO membrane. A high recovery
seawater RO desalination system has been developed in Japan. The system is based on two