solids and may be adjusted to remove arsenic. 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 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. 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 resins are 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. subterranean arsenic removal (sar) technology sar technology in subterranean arsenic removal, aerated groundwater is recharged back into the aquifer to create an oxidation zone which can trap iron and arsenic on the soil particles through adsorption process. the oxidation zone created by aerated water boosts the activity of the arsenic-oxidizing microorganisms which can oxidize arsenic from +3 to +5 state sar technology. no chemicals are used and almost no sludge is produced during operational stage since iron and arsenic compounds are rendered inactive in the aquifer itself. thus toxic waste disposal and the risk of its future mobilization is prevented. also, it has very long operational life, similar to the long lasting tube wells drawing water from the shallow aquifers. six such sar plants, funded by the world bank and constructed by ramakrishna vivekananda mission, barrackpore & queen's university belfast, uk are operating in west bengal. each plant has been delivering more than 3,000 liters of arsenic and iron-free water daily to the rural community. the first community water treatment plant based on sar technology was set up at kashimpore near kolkata in 2004 by a team of european and indian engineers led by bhaskar sen gupta of queen's university belfast for tipot. sar technology had been awarded dhirubhai ambani award, 2010 from icheme uk for chemical innovation. again, sar was the winner of the st. andrews award for environment, 2010. the sar project was selected by the blacksmith institute – new york & green cross- switzerland as one of the "12 cases of cleanup & success" in the world's worst polluted places report 2009. (refer: www.worstpolluted.org). currently, large scale sar plants are being installed in us, malaysia, cambodia, and vietnam. nanotechnology based arsenic remediation nanomaterials with intrinsically high surface energy prepared using naturally abundant ingredients can be helpful in creating green products. using nanomaterials, it is possible to effectively destroy microorganisms, adsorb arsenic and fluoride, remove heavy metals and degrade pesticides usually found in water. researchers have looked at new methods to synthesize iron oxide/hydroxide/oxyhydroxide compositions in the laboratory and used them for water purification. a product aptly titled, amrit, meaning elixir in indian languages, developed by the indian institute of technology madras, is an affordable water purification technology based on advanced materials, which has been validated through research articles and patents and has been approved for national implementation in india. the technology can remove several anions, especially arsenate and arsenite (two common species present in arsenic-contaminated water) and fluoride from water. currently, this technology is delivering arsenic-free water to about 10,00,000 people every day. amrit uses an adsorbent based on a simple method to maintain the metastable 2-line ferrihydrite (named as cm2lf) phase at room temperature, by confining it in biopolymeric cages. it can handle concentrations of arsenic and colloidal iron reaching up to 100-800 µg/l and 50 mg/l, respectively and brings the output concentration below the permissible limit set by epa of 10 µg/l and 200 µg/l, respectively. the arsenic adsorption capacity of the composite is 1.4 to 7.6 times better than the available compositions, in field conditions. hundreds of units have been tested in the arsenic belt of india which are continuously running in the field for several years. complete water purification units in various capacities ranging from tens of liters to millions of liters have been implemented. amrit has been applied in various forms of community water purifiers, which are easy to use, have a low cost of maintenance and generates zero sludge. it can be operated at 300 lph (liters per hour) to 100,000 lph flow rates. the cost of clean water using this technology in the arsenic affected areas is under 2.5 paisa ($0.0006) per liter which includes the cost of the operator running the plant, necessary consumables, and electricity used for pumping and distribution. no electricity is needed for filtration. it can be implemented at any level - domestic, community, or municipal – levels anywhere in the world and can be integrated easily with other technologies. the adsorption properties of cm2lf and its uptake mechanism have been investigated thoroughly. subsequent research on making this technology greener with further improvement in removal capacity and inclusion of sustainability metrics in the manufacture and operation has been reported. in its entirety, amrit provides a compelling solution for achieving the united nations millennium development goal of sustainable access to safe drinking water. research mapping in 2008, the swiss aquatic research institute, eawag, presented a new method by which hazard maps could be produced for geogenic toxic substances in groundwater. this provides an efficient way of determining which wells should be tested. in 2016, the research group made its knowledge freely available on the groundwater assessment platform (gap). this offers specialists worldwide the possibility of uploading their own measurement data, visually displaying them and producing risk maps for areas of their choice. gap also serves as a knowledge-sharing forum for enabling further development of methods for removing toxic substances from water. dietary intake researchers from bangladesh and the united kingdom have claimed that dietary intake of arsenic adds a significant amount to total intake where contaminated water is used for irrigation.