AWWA ACE58300

Bench-scale studies were conducted to evaluate the effects of several process variables, such as reaction pH, adsorbent dosage, and particle size of the media on the kinetics of adsorption and treatment efficiency of a process for removing arsenic (III) and arsenic (V) from contaminated groundwater by adsorption onto Granular Ferric Hydroxide (GFHTM). The concentrations of dissolved arsenic in the samples were analyzed using the Inductively Coupled Plasma - Mass Spectroscopy (ICP-MS) method, which is capable of detecting arsenic concentrations as low as 1.5 ug/L. The results reveal that GFH media is capable of removing both arsenic (III) and arsenic (V), and is effective over a wide pH range. The adsorption of arsenic (III) is less pH-dependent than that of arsenic (V). Kinetics data indicate that the reaction is fast, and the rate of adsorption of arsenic (III) and arsenic (V) onto both pulverized and "as received" GFH media can be approximated by first-order kinetics. The adsorption characteristics of the media were analyzed and evaluated using the Freundlich adsorption isotherm equation. The regression coefficients demonstrate that the Freundlich model fits both the arsenic (III) and arsenic (V) experimental results reasonably well. The rates of adsorption and the treatment efficiency are a function of reaction pH, media dosage, and particle size. Results of the U.S. Environmental Protection Agency's Toxic Characteristic Leaching Procedure (TCLP) test showed that the concentrations of arsenic in the TCLP extracts were less than the regulatory limit of 5 mg/L. GFH media can be used to directly treat groundwater or can be added to an existing water treatment system as a polishing unit without impacting the existing operation. Includes 21 references, tables, figures.