Environmental context
Arsenic contamination of aquifers is a worldwide public health concern and several technologies have been developed to reduce the arsenic content of groundwater. We investigated the efficiency of various materials for arsenic removal from groundwater and found that iron-based sorbents have great affinity for arsenic even if groundwater composition can depress their ability to bind arsenic. Moreover, we showed that the use of microorganisms can enhance the removal of arsenic from groundwater.
Abstract
The AsIII and AsV adsorption capacity of biochar, chabazite, ferritin-based material, goethite and nano zero-valent iron was evaluated in artificial systems at autoequilibrium pH (i.e. MilliQ water without adjusting the pH) and at approximately neutral pH (i.e. TRIS-HCl, pH 7.2). At autoequilibrium pH, iron-based sorbents removed 200μgL–1 As highly efficiently whereas biochar and chabazite were ineffective. At approximately neutral pH, sorbents were capable of removing between 17 and 100% of AsIII and between 3 and 100% of AsV in the following order: biochar<chabazite<ferritin-based material<goethite<nano zero-valent iron. Chabazite, ferritin-based material and nano zero-valent iron oxidised AsIII to AsV and ferritin-based material was able to reduce AsV to AsIII. When tested in naturally As-contaminated groundwater, a marked decrease in the removal effectiveness occurred, due to possible competition with phosphate and manganese. A biological oxidation step was then introduced in a one-phase process (AsIII bio-oxidation in conjunction with AsV adsorption) and in a two-phase process (AsIII bio-oxidation followed by AsV adsorption). Arsenite oxidation was performed by resting cells of Aliihoeflea sp. strain 2WW, and arsenic adsorption by goethite. The one-phase process decreased As in groundwater to 85%, whereas the two-phase process removed up to 95% As, leaving in solution 6μgL–1 As, thus meeting the World Health Organization limit (10μgL–1). These results can be used in the scaling up of a two-phase treatment, with bacterial oxidation of As combined to goethite adsorption.
Effectiveness of various sorbents and biological oxidation in the removal of arsenic species from groundwater
