AWWA ACE63030

AWWA ACE63030 Removal of Co-Occurring Ions During Arsenic Treatment
Conference Proceeding by American Water Works Association, 06/01/2006

Westerhoff, Paul; Benn, Troy; Kahn, Naeem; Hristovski, Kiril

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Packed-bed adsorptive treatment systems for arsenic removal will be widely employed.We have been conducting rapid small scale column tests (RSSCTs) on many adsorptivemedia, and frequently track the removal of vanadium, phosphate, silica, and uranium.Phosphate is reported to compete for arsenic adsorption sites. Silica affects surfacecharge and arsenic removal. Vanadium is listed on the US Environmental Protection Agency (USEPA) Candidate Contaminant List(CCL2), and some states currently have vanadium regulations. The regulation foruranium has only recently been enforced. All of these elements co-occur with arsenic ingroundwaters. This paper includes batch adsorption data and RSSCTbreakthrough curves for these co-occurring ions from natural groundwaters andexperiments with model waters. A few brief examples of the findings from continuousflow RSSCTs are summarized as follows:ArsenxNP (a iron-modified hybrid ion exchange resin) removed uranium andarsenic for ~ 25,000 bed volumes, iron (E33) and titanium (Adsorbsia GTO,MetsorbG) medias only removed uranium for 1000 bed volumes althougharsenic was removed for 20,000 bed volumes, experiments were just initiatedon a separate groundwater to evaluate uranium removal using GFH, E33,MetsorbG, and ArsenxNP; GFH removes more phosphate and silica than E33;GFH removes As(III) significantly better than E33 GFH removes more vanadium than any of the other media,Batch tests have recently been conducted to compare vanadium removal by different ironand titanium based media. Adsorption isotherms were developed at multiple vanadiumconcentrations and variable adsorbent dosages.As the drinking water community begins to treat groundwaters for arsenic, renewedattention to the behavior of other trace elements is emerging as an important issue forseveral reasons. First, these elements potentially affect/compete for arsenic adsorptionsites. Second, these elements accumulate in the adsorbent media and may affect theability to dispose of the media to landfills. Third, it may be necessary to design treatmentsystems capable of removing these elements as current regulations become enforced andas regulations for other elements (vanadium, molybdenum, selenium) are evaluated. Includes 30 references, figures.