Changes

'''Coagulation/filtration''' (also known as [[flocculation#Water_treatment|flocculation]]) removes arsenic by [[coprecipitation]] and adsorption using iron coagulants. Coagulation/filtration using [[alum]] is already used by some utilities to remove suspended solids and may be adjusted to remove arsenic. But the problem of this type of filtration system is that it gets clogged very easily, mostly within two to three months. The toxic arsenic sludge are disposed of by concrete stabilization, but there is no guarantee that they won't leach out in future.

'''[[Iron oxide adsorption]]''' filters the water through a granular medium containing ferric oxide. Ferric oxide has a high affinity for adsorbing dissolved metals such as arsenic. The iron oxide medium eventually becomes saturated, and must be replaced. The sludge disposal is a problem here too.

'''[[Activated alumina]]''' is an adsorbent that effectively removes arsenic. Activated alumina columns connected to shallow tube wells in India and Bangladesh have successfully removed both As(III) and As(V) from groundwater for decades. Long-term column performance has been possible through the efforts of community-elected water committees that collect a local water tax for funding operations and maintenance.<ref>{{cite journal|last=SARKAR|first=S|coauthors=GUPTA, A, BISWAS, R, DEB, A, GREENLEAF, J, SENGUPTA, A|title=Well-head arsenic removal units in remote villages of Indian subcontinent: Field results and performance evaluation|journal=Water Research|date=1 May 2005|volume=39|issue=10|pages=2196–2206|doi=10.1016/j.watres.2005.04.002}}</ref> It has also been used to remove undesirably high concentrations of fluoride.

'''[[Ion Exchange]]''' has long been used as a water-softening process, although usually on a single-home basis. Traditional anion exchange is effective in removing As(V), but not As (III), or [[arsenic trioxide]], which doesn't have a net charge. Effective long-term ion exchange removal of arsenic requires a trained operator to maintain the column.

Both '''[[Reverse osmosis]]''' and '''[[electrodialysis]]''' (also called ''electrodialysis reversal'') can remove arsenic with a net ionic charge. (Note that arsenic oxide, As₂O₃, is a common form of arsenic in groundwater that is soluble, but has no net charge.) Some utilities presently use one of these methods to reduce [[total dissolved solids]] and therefore improve taste. A problem with both methods is the production of high-salinity waste water, called [[brine]], or concentrate, which then must be disposed of.