Abstract
The co-occurrence of arsenic (As) and organic ligands in water bodies has raised environmental concerns due to their toxicity and adverse effects on human health. The present study aims to elucidate the influences of hydrophobic/hydrophilic organic ligands, such as humic acid (HA) and salicylic acid (SA), on the interactive behavior of As species in water. Moreover, the competitive removal behaviors of As(III, V) species and total organic carbon (TOC) were systematically investigated by coagulation-flocculation-sedimentation (C/F/S) under various aqueous matrices. The results showed the stronger binding affinity of As(V) than As(III) species, with a higher complexation ability of hydrophobic ligands than hydrophilic. The media containing hydrophilic ligands require smaller ferric chloride (FC) doses to achieve the higher As(III, V) removal, while the optimum FC dose required for As(III) removal was found to be higher than that for As(V). Moreover, hydrophobic ligands showed higher TOC removal than hydrophilic ligands. The pronounced adverse effect of a higher concentration of hydrophobic ligands on the removal efficiencies of As(V) and TOC was observed. The adsorption of As(V) on Fe precipitates was better fitted with the Langmuir model but the Freundlich isotherm was more suitable for As(III) in the presence of hydrophilic SA. Moreover, TOC removal was substantially decreased in the As(V) system as compared to the As(III) system due to the dissolution of Fe precipitates at higher As(V) concentrations. The results of FC composite flocs demonstrated that the combined effect of oxidation, charge neutralization and adsorption played an important role in the removal of both toxicants during the C/F/S process. In summary, the findings of the present study provide insights into the fate, mobility and competitive removal behavior of As(III, V) species and organic ligands in the water treatment process.
Highlights
In recent years, environmental contamination by arsenic (As) has attracted substantial attention, due to its ubiquity and acute toxicity to human health [1]
We examined the interactive behavior of As(III, V) species with hydrophobic/hydrophilic organic ligands (HA and salicylic acid (SA)) in an aqueous environment
We systematically investigated the competitive removal behavior of As(III, V) species and total organic carbon (TOC) by coagulation-flocculation-sedimentation (C/F/S) in a heterogeneous aqueous environment
Summary
Environmental contamination by arsenic (As) has attracted substantial attention, due to its ubiquity and acute toxicity to human health [1]. The water streams in the Stampede and Slate Creek watersheds in the Kantishna Hills mining district in Alaska, USA, presented As contamination of around 720 μg/L [4]. As levels around 285 μg/L were found in the groundwater near abandoned antimony mines in Slovakia [7]. The potential adverse health effects of the oral uptake of such water-soluble As in the human body include gastrointestinal problems and carcinoma of the liver, lung, skin, bladder and kidney [8]. World Health Organization (WHO) and United States Environmental Protection Agency (USEPA) have set the regulatory standard for As in drinking water at 10 μg/L [3]
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