Arsenic removal from groundwater with iron tailored granular activated carbon preceded by pre-corroded steel

Arsenic of over 50 ppb level in drinking water could cause a lifetime risk of dying from cancer for the consumer. Although, conventional granular activated carbon (GAC) has a very limited capacity for removing arsenic, it was found that tailoring GAC by preloading iron could enhance its bed life, when the iron tailored GAC was coupled with precorroded iron, the GAC's bed life could greatly enhanced.;For carbon tailoring, incipient wetness method and organic-iron preloading method were employed. 1--3% Fe loading was achieved with organic-iron preloading method and 3--6% Fe loading was achieved via incipient wetness method. Compared with virgin GAC, the citric acid-iron preloaded GAC could extend the GAC's bedlife by over 20 times to 7000 bed volumes of 50 ppb arsenic containing water processed before 10 ppb breakthrough. The incipient wetness method could further extend the GAC's bedlife by 2 times.;Precorroded iron material, coupled with Organic carboxyl-Fe preloaded granular activated carbons (GAC), have been appraised as an innovative technique for removing arsenic from groundwater. The effective precorroded iron materials have included Galvanized Steel Fittings and Perforated Steel Sheets. Rapid Small Scale Column Tests (RSSCT's) and mini column tests had been conducted to evaluate the arsenic removal capacity of the procorroded iron coupled with tailored carbon. The arsenic was found to be removed by both the iron column and the GAC column, with GAC column as the major absorber. The pH, idling and precorrosion protocol affect the iron release and arsenic removal. The combination of a precorroded iron column followed by a iron -- tailored GAC column removed arsenic to below 10 ppb for as much as 248,000 bed volumes (BVs) at pH 6. These tests employed Rutland, MA groundwater with native As of 47 ∼ 55 ppb. Idling the system for one time extended the bed life of by 2 time, but caused a short period arsenic breakthrough after column restart.;Arsenic removal in the GAC column was proportional to the iron amount accumulated in the GAC column. The iron amount accumulated in the GAC column was generally controlled by the operating pH, but was also affected by the precorrosion conditions of the iron and the idling of the system. The arsenic removal in the iron column was generally higher with lower pH. Moreover, as the column just started up, the removal was also controlled by the iron pre-corrosion condition. A longer precorrosion period has promoted arsenic removal in the iron column. The arsenic removal was generally lower with aged PSSs as the column just started, this was attributed to the release of iron (hydr)oxides particles from the iron column; but with longer aging period of more than 10 days, arsenic removal by aged PSSs could be greatly increased.;The precorrosion protocol influenced the formation of surface corrosion layer of the iron, which in turn, affected how the iron was released and accumulated in the GAC column, especially when the column just restarted. The morphology and structure of surface corrosion products on precorroded steel sheets were studied via scanning electron microscope (SEM), X-ray diffraction (XRD) and X-ray photoelectron spectroscopy (XPS) method. The results showed that the morphology of surface corrosion products was highly related to iron release and arsenic removal. Fresh precorroded steel sheets have a uniform surface, while aged precorroded steel sheets exhibited a heterogeneous surface with some areas covered with thick, porous scales. Lepidocrocite (gamma-FeOOH), humboditine (FeC2O4(H2O)2) and clinoferrosilite (Fe1.5Mg0.5Si2O6) are the mainly component on the fresh precorroded steel sheet, while goethite (alpha-FeOOH), lepidocrocite and magnetite (Fe3O4) are the primary component of the aged precorroded steel sheet surface. After they were employed in the column for arsenic removal, the primary phase on precorroded steel sheet changed to goethite and magnetite, calcite was also detected. Arsenic extracted from precorroded steel in iron columns contain only As(III) when the column was operated at pH < 7 and had been idled. XAFS study of the GAC in pH 7.5 column indicated the presence of reduced iron phases such as FeO and green rust, some As(V) has also been reduced to As(III). Idling the columns for 7 days is promoted a reduction reaction in both the iron and the GAC columns.