Arsenic removal from water/wastewater using adsorbents—A critical review

Remediation of inorganic arsenic in groundwater for safe water supply: A critical assessment of technological solutions

Rice husk has tremendous potential as a remediation material for the removal of arsenic from groundwater. The present work investigates the possibility of the use of rice husk adsorption technology without any pretreatment in the removal of arsenic from aqueous media. Various conditions that affect the adsorption/desorption of arsenic are investigated. Adsorption column methods show the complete removal of both As(III) and As(V) under the following conditions:  initial As concentration, 100 μg/L; rice husk amount, 6 g; average particle size, 780 and 510 μm; treatment flow rate, 6.7 and 1.7 mL/min; and pH, 6.5 and 6.0, respectively. The desorption efficiencies with 1 M of KOH after the treatment of groundwater were in the range of 71−96%. The present study might provide new avenues to achieve the arsenic concentrations required for drinking water recommended by Bangladesh and the World Health Organization (WHO).

Removal of Arsenic in Aqueous Solutions by Adsorption onto Waste Rice Husk

Removal of anionic pollutants from liquids by biomass materials: A review

The current United States maximum contaminant level for arsenic in drinking water is set at 50 μg/l. Because of the cancer risks involved, Canada has already lowered the maximum contaminant level to 25 μg/l; the United States Environmental Protection Agency is reviewing the current allowable level for arsenic with a view of lowering it significantly. Various treatment methods have been adopted to remove arsenic from drinking water. These methods include 1) adsorption-coprecipitation using iron and aluminum salts, 2) adsorption on activated alumina, activated carbon, and activated bauxite, 3) reverse osmosis, 4) ion exchange and 5) oxidation followed by filtration. Because of the promise of oxidation-filtration systems, column studies were conducted at the University of Regina to examine oxidation with KMnO 4 followed by filtration using manganese greensand and iron-oxide coated sand to examine the removal of arsenic from drinking water; these results were compared with the data from ion exchange studies. These studies demonstrated that As (III) could be reduced from 200 μg/l to below 25 μg/l by the manganese greensand system. In the case of manganese greensand filtration, addition of iron in the ratio of 20:1 was found necessary to achieve this removal.

Arsenic in drinking water: problems and solutions.

Equilibrium adsorption isotherms of As(III) were obtained from the experimentally generated data on activated alumina and activated carbon at temperature 303 K and pH 7.4. The isotherm for As(III) on activated alumina was typically of Brunauer Type – I but in the case of activated carbon equilibrium capacity seems to be increasing with increase in concentration. Langmuir isotherm model best represents the experimental data for As(III) in activated alumina and Freundlich model in activated carbon. Model parameters such as saturation capacity of adsorbent qs, Langmuir constant b, and Freundlich constants K and n were determined. Saturation adsorption capacity of As(III) in activated carbon was much higher than that in activated alumina. Overall effective mass transfer coefficient k was determined using uptake rate method. It is observed that k was independent of concentration of As(III). Values of k for both the adsorbents are of the order of 10−2 min−1.

M. H. Sadique

Papers

Equilibrium and kinetics studies for As(III) adsorption on activated alumina and activated carbon.