Low‐Level Arsenic Removal from Drinking Water

The reported ability of cysteine and cystine to bind typical arsenic oxy‐ions in water is used as a basis for a study of the potential for using a surfactant with a cysteine head‐group for selective arsenic binding and removal in an ion flotation process. Several different head‐group attachment methods are studied with cysteine and cystine and with single‐ and double‐chain surfactants. A comparison of the properties of these surfactants with some other surface‐active compounds, with groups like those on cysteine, suggest that few compounds have suitable characteristics for the efficient removal of low levels of arsenic from drinking water. An amino‐acid‐based single‐chain surfactant is synthesized by reacting cysteine with octanoyl chloride to obtain octanoyl cysteine, which is then used in a study of selective ion flotation for the removal of low levels of arsenic from drinking water. This compound has high water solubility and causes extensive foaming in a typical flotation chamber and removed 99.4–99.9% of the 5 mg L−1 arsenic present in the contaminated water in a simple, single‐stage ion flotation process, using either air or nitrogen gas. These laboratory results indicate that these surfactants can be useful in the large‐scale treatment of low‐level arsenic‐contaminated water. This report shows how low levels of As ions in contaminated drinking water can be almost completely removed with a simple ion flotation process, using a specifically designed cysteine head‐group, biodegradable surfactant. This single‐step process can be used to convert drinking water contaminated with 5 ppm As levels to internationally acceptable levels.