Efficient methods for arsenic removal from groundwater

Abstract

Arsenic may be found in water that has fl owed through arsenic-rich rocks. Arsenic is a toxic, trace element that is ubiquitous in nature. It can easily be transported from the sediment to the surrounding pore-water. Severe health effects have been observed in populations drinking arsenic-rich water over long periods in countries worldwide. A 2007 study found that over 137 million people in more than 70 countries are probably affected by arsenic poisoning of drinking water. In groundwater, arsenic combines with oxygen to form inorganic pentavalent arsenate and trivalent arsenite. Most arsenic treatments fall into four process categories: ion exchange, membrane process, adsorption, or chemical precipitation. This study investigates the potential of removing arsenic from groundwater by using two process categories ‐ activated alumina and lime softening. Arsenic adsorption by commercially available activated alumina is surveyed and its effi ciency investigated. We have incorporated some of the valuable literature on arsenic remediation by adsorption. According to results of three activated alumina pilot studies, considering infl uence of adsorption time, temperature, pH, alumina quantity, arsenic concentration, and different alumina production resources, it has high effi ciency for arsenic removal. Adsorption isotherm for both species of arsenic (III and V) is compatible with both Freundlich and Langmuir models (correlation coeffi cient >0.93). The prevalent pH range for arsenate was between 6 and 8. Modifi ed activated alumina can remove arsenate at the infl uent pH of 8.1 ± 0.4 to below the maximum concentration level (MCL). The exhausted media passed the Toxicity Characteristic Leaching Procedure (TCLP) test with respect to arsenic. Lime softening operated within the optimum pH range of more than 10.5 is likely to provide a high percentage of arsenic removal (90%) for infl uent concentrations of up to 0.05 mg/L. It may be diffi cult to reduce consistently to 0.01 mg/L by lime softening alone. Systems using lime softening may require secondary treatment to meet that goal.