Membrane and Desalination Technologies - TCE Moodle Website

Membrane Technologies for Point-of-Use and Point-of-Entry Applications 613
Table 14.5
List of impurities that can be removed by reverse osmosis (adapted from Kneen et al. (30))
Ions and metals Organic chemicals
Arsenic (As) Aluminum (Al) Benzene
Barium (Ba) Bicarbonate (HCO3 ) Carbon tetrachloride
Cadmium (Cd) Calcium (Ca) Dichlorobenzene
Carbonate (CO3 2 ) Chloride (Cl) MTBE
Chromium (Cr) Copper (Cu) Toluene
Fluoride (F) Iron (Fe) Trichloroethylene
Lead (Pb) Magnesium (Mg) Total trihalomethanes (THMs)
Manganese (Mn) Mercury (Hg) Pesticides
Nitrate/nitrite (NO3 /NO2 ) Potassium (K) 1,2,4-trichlorobenzene
Radium (Ra) Selenium (Se) 2,4-D
Silver (Ag) Sodium (Na) Atrazine
Sulfate (SO4 2 ) Zinc (Zn) Endrin
Particles Heptachlor
Asbestos Protazoan cysts Lindane
Pentachlorophenol
earth’s surface. The dissolved minerals can produce an unpleasant taste or appearance and
can contribute to scale deposits on pipe walls. The only effective means of reducing TDS is
by using RO.
Arsenic (AS): Arsenic (As) is a naturally occurring contaminant found in many groundwaters
in two forms (valences or oxidation states): pentavalent arsenic (also known as As(V),
As 5þ , or arsenate) and trivalent arsenic (also known as As(III), As 3þ , or arsenite). In some
occasion, a combination of both can be found in groundwater. Although both forms of arsenic
are potentially harmful to human health, trivalent arsenic is considered more harmful than
pentavalent arsenic. It is important for consumers to determine which type of arsenic is
present in their water prior to selecting a water treatment device. When pentavalent arsenic is
found in water, either reverse osmosis or distillation can be selected. RO is considered the
effective treatment in POU/POE systems to remove this contaminant species.
Iron: Iron is frequently found in drinking water. It is introduced from iron pipes in the
water distribution system. Iron in drinking water can give a rusty color to laundered clothes
and may affect taste. In the presence of hydrogen sulfide, iron causes a sediment to form that
may give the water a blackish color. Iron exists in natural groundwater in the soluble (ferrous)
state but when exposed to oxygen, it is converted into the insoluble (ferric) state with its
characteristic reddish brown or rusty color. If allowed to stand long enough, this rusty
sediment will usually settle to the bottom of a container; however, it is difficult to use this
type of settling to remove the iron. RO is also an effective treatment method to remove iron
from drinking water.
Chloride: Chlorides in groundwater can be naturally occurring in deep aquifers or caused
by pollution from seawater, brine, or industrial or domestic wastes. Chloride concentration