New methods to remediate arsenic-contaminated water continue to be studied, particularly to fill the need for accessible methods that can significantly impact developing communities. A combination of cactus mucilage and ferric (Fe(III)) salt was investigated as a flocculation-coagulation system to remove arsenic (As) from water. As(V) solutions, ferric nitrate, and mucilage suspensions were mixed and left to stand for various periods of time. Visual and SEM observations confirmed the flocculation action of the mucilage as visible flocs formed and settled to the bottom of the tubes within 3 min. The colloidal suspensions without mucilage were stable for up to 1 week. Sample aliquots were tested for dissolved and total arsenic by ICP-MS and HGAFS. Mucilage treatment improved As removal (over Fe(III)-only treatment); the system removed 75-96% As in 30 min. At neutral pH, removal was dependent on Fe(III) and mucilage concentration and the age of the Fe(III) solution. The process is fast, achieving maximum removal in 30 min, with the majority of As removed in 10-15 min. Standard jar tests with 1000 μg/L As(III) showed that arsenic removal and settling rates were pH-dependent; As removal was between 52% (high pH) and 66% (low pH).

The development of effective and alternative water purification systems of low cost is extremely desired. There are several communities that could benefit from water purification methods that use renewable, sustainable, low-toxicity, and low-cost technology. This study investigates separation based on cactus mucilage as an emergency response biomaterial to provide clean drinking water for communities affected by natural disasters. The mucilage is extracted from the Opuntia ficus-indica cactus, commonly known as nopal or prickly pear. This readily available and inexpensive natural extract has been shown to remove sediments, bacteria, and arsenic from contaminated water, in previous studies. Samples of tap water (from a treatment center), well water, surface water, and distributed water (bottled water and water from tanker trucks) were collected from 10 different locations at Port-au-Prince, Haiti. A wide-range analysis of elements was performed on acidified samples to determine the water quality and type of contamination. Iron, boron, barium, and selenium were found at some sites with concentrations above the maximum contaminant level and provisional guidelines recommended by the United States Environmental Protection Agency (USEPA, 2009). Simple batch experiments were performed with two mucilage extracts from O. indica-ficus (gelling and nongelling extracts (GE, NE)). Analysis of samples from the topmost layer of water batches treated with the mucilage revealed that high metal-removal rates were achieved using both NE and GE. Cactus mucilage effectively decreased the hazardous metal content to levels acceptable to water quality agencies.

High concentrations of arsenic in groundwater continue to present health threats to millions of consumers worldwide. Particularly, affected communities in the developing world need accessible technologies for arsenic removal from drinking water. We explore the application of cactus mucilage, pectic polysaccharide extracts from Opuntia ficus-indica for arsenic removal. Synthetic arsenate (As (V)) solutions were treated with two extracts, a gelling extract (GE) and a nongelling extract (NE) in batch trials. The arsenic concentration at the air-water interface was measured after equilibration. The GE and NE treated solutions showed on average 14% and 9% increases in arsenic concentration at the air-water interface respectively indicating that the mucilage bonded and transported the arsenic to the air-water interface. FTIR studies showed that the -CO groups (carboxyl and carbonyl groups) and -OH (hydroxyl) functional groups of the mucilage were involved in the interaction with the arsenate. Mucilage activity was greater in weakly basic (pH 9) and weakly acidic (pH 5.5) pH. This interaction can be optimized and harnessed for the removal of arsenic from drinking water. This work breaks the ground for the application of natural pectic materials to the removal of anionic metallic species from water.