Removal of arsenic from drinking water

Arsenic contamination of surface and subsurface waters, human health effects due to arsenic toxicity, and the enforcement of stringent standards by the regulatory agencies call for a pragmatic approach in developing a suitable and cost-effective technology to remove arsenic from the drinking water. Elevated concentrations of arsenic in drinking water have been reported in many parts of the world. The drinking water standard for arsenic has been lowered in many countries to less than 25 μg/L. A reduction in acceptable consumption levels of arsenic by the regulatory agencies is forcing water utilities to identify and implement cost-effective arsenic removal technologies.; The objective of the present research was to assess the potential and effectiveness of the adsorbents in removing arsenite [As(III)] and arsenate [As(V)] to a level of less than 5 μg/L in drinking water supplies of small communities. The adsorbents used in the research study were iron oxide-coated sand-1 & 2 (10CS-1 & 2), granular ferric hydroxide (GFH), ferrihydrite (FH) and granular ferrihydrite (GFT). All of the adsorbents except GFH were prepared in the laboratory. Tap water (from the City of Regina, Saskatchewan) and raw water containing arsenic from Kelliher, Saskatchewan were used in the batch and column studies. Experimental data from isotherm studies fitted well with the Freundlich, the Langmuir, and the Redlich-Peterson isotherms, indicating a favorable adsorption by the adsorbents. Less than 5 μg/L [for both As(III) and As(V)] was achieved in the batch studies, after a contact period of 6 hours with the adsorbents.; Column studies were conducted at normal filtration rates to study the removal of arsenic species. In the column studies using IOCS-2 and GFH, a longer run of the column, high bed volumes and arsenic removal up to 5 μg/L were obtained. However, the performance of IOCS-2 was better than that of GFH with respect to bed volumes achieved and adsorption capacity. The adsorption capacities of IOCS-2 estimated for As(III) and As(V) were 0.74 and 0.72 mg/g IOCS-2, respectively. In the column studies with Kelliher water using IOCS-2 and GFH, a level of less than 5 μg/L of effluent arsenic was obtained. High bed volumes (1720) up to a breakthrough concentration of 5 μg/L were achieved in the studies with natural water using IOCS-2. Column studies with granular ferrihydite showed that As(V) removal was better compared to As(III) removal with respect to the number of bed volumes achieved up to an effluent arsenic level of 25 μg/L. The study demonstrated conclusively that iron oxide-coated sand and granular ferric hydroxide are excellent media for reducing arsenic concentration to less than 5 μg/L from drinking water.